Reference

AlllQl 7aSE13

NB3

Publi

NATL INST OF STANDARDS & TECH R.I.C.

A1 11 01 78521

3

Rlsley, A. S/The National Measurement sy QC100 .U57 V445-1;1976 C.2 NBS-PUB-R 197 ;PECIAL PUBLICATION 445-1

U.S. DEPARTMENT OF COMMERCE / National Bureau of Standards

The National

Measurement System

for Time and Frequency
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards* was established by an act of Congress March 3, 1901. The Bureau's overall goal is to strengthen and advance the Nation's science and technology

and facilitate their effective application for public benefit. To this end, the Bureau conducts

research and provides: (1) a basis for the Nation's physical measurement system, (2) scientific and technological services for industry and government, (3) a technical basis for equity in trade, and (4) technical services to promote public safety. The Bureau consists of the Institute for Basic Standards, the Institute for Materials Research, the Institute for Applied Technology,

the Institute for Computer Sciences and Technology, and the Office for Information Programs.

THE INSTITUTE FOR BASIC STANDARDS provides the central basis within the United

States of a complete and consistent system of physical measurement; coordinates that system

with measurement systems of other nations; and furnishes essential services leading to accurate and uniform physical measurements throughout the Nation's scientific community, industry,

and commerce. The Institute consists of the Office of Measurement Services, the Office of Radiation Measurement and the following Center and divisions:

Applied Mathematics — Electricity — Mechanics — Heat — Optical Physics — Center

for Radiation Research: Nuclear Sciences; Applied Radiation — Laboratory Astrophysics ^ — Cryogenics ^ — Electromagnetics ^ — Time and Frequency

THE INSTITUTE FOR MATERIALS RESEARCH conducts materials research leading to improved methods of measurement, standards, and data on the properties of well-characterized materials needed by industry, commerce, educational institutions, and Government; provides

advisory and research services to other Government agencies; and develops, produces, and

distributes standard reference materials. The Institute consists of the Office of Standard Reference Materials, the Office of Air and Water Measurement, and the following divisions:

Analytical Chemistry — Polymers — Metallurgy — Inorganic Materials — Reactor

Radiation — Physical Chemistry.

THE INSTITUTE FOR APPLIED TECHNOLOGY provides technical services to promote

the use of available technology and to facilitate technological innovation in industry and

Government; cooperates with public and private organizations leading to the development of

technological standards (including mandatory safety standards), codes and methods of test; and provides technical advice and services to Government agencies upon request. The Insti- tute consists of the following divisions and Centers: Standards Application and Analysis — Electronic Technology — Center for Consumer

Product Technology: Product Systems Analysis; Product Engineering — Center for Building

Technology: Structures, Materials, and Life Safety; Building Environment; Technical Evaluation and Application — Center for Fire Research: Fire Science; Fire Safety Engineering.

THE INSTITUTE FOR COMPUTER SCIENCES AND TECHNOLOGY conducts research and provides technical services designed to aid Government agencies in improving cost effec- tiveness in the conduct of their programs through the selection, acquisition, and effective utilization of automatic data processing equipment; and serves as the principal focus within

the executive branch for the development of Federal standards for automatic data processing

equipment, techniques, and computer languages. The Institute consists of the following

divisions: Computer Services — Systems and Software — Computer Systems Engineering — Information Technology.

THE OFFICE FOR INFORMATION PROGRAMS promotes optimum dissemination and

accessibility of scientific information generated within NBS and other agencies of the Federal Government; promotes the development of the National Standard Reference Data System and

a system of information analysis centers dealing with the broader aspects of the National Measurement System; provides appropriate services to ensure that the NBS staff has optimum

accessibility to the scientific information of the world. The Office consists of the following

organizational units: Office of Standard Reference Data — Office of Information Activities — Office of Technical

Publications — Library — Office of International Relations — Office of International Standards.

^ Headquarters and Laboratories at Gaithersburg, Maryland, unless otherwise noted; mailing address Washington, D.C. 20234.

2 Located at Boulder, Colorado 80302.
The National Measurement System

for Time and Frequency

NATIONAL BtTREAU OF STANDARDS

LIBRARY JUL 7 7976 .

Spec '0^1 /^i^6//<ix3t-^/oru yio . -iH^- /

Allan S. Risley

Time and Frequency Division

Institute for Basic Standards

National Bureau of Standards

Boulder, Colorado 80302

U.S. DEPARTMENT OF COMMERCE, Elliot L. Richardson, Secretary

Dr. Betsy Ancker-Johnson, Assisfant Secretary for Science and Technology

uS NATIONAL BUREAU OF STANDARDS, Ernest Ambler, kcWnq Director

Issued June 1976
Library of Congress Catalog Card Number: 76-608114

National Bureau of Standards Special Publication 445-1

Nat. Bur. Stand. (U.S.), Spec. Publ. 445-1, 72 pages (June 1976) CODEN: XNBSAV

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1976

For sale by ihe Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 (Order by SD Catalog No. CI 3.10:443-1). Price $1.20 (Add 25 percent additional for other than U.S. mailing).
FOREWORD

This is one of the reports from the 1972-75 NBS Study of the National Measurement

System. It deals specifically with the current structure, status, and trends of the

system used in this country for the measurement of time and frequency and closely

related quantities, such as position (navigation).

The "Concept of a National Measurement System" has been discussed by NBS authors

and spokesmen for a number of years, since the publication by Dr. R. D. Huntoon of

an article by that title in the October 6, 1967 issue of Science (Vol. 158, No. 3797, pages 67-71). Dr. Huntoon began his article with the following paragraph:

"Concurrently with the growth and industrialization of this nation, there has

developed within it a vast, complex system of measurement which has made

possible the very growth that brought the system into being. This National

Measurement System (NMS) stands today as one of the key elements in a worldwide measurement system that links all major nations together in a consistent,

compatible network for communication and trade."

The U. S. National Measurement System is defined as comprising all of the activities

and mechanisms--intel lectual and operational, technical and institutional --used

by this country to produce the physical measurement data needed to create the objective, quantifiable knowledge required by our society. This knowledge is used to describe, predict, communicate, control, and react, in many aspects of our personal

and social lives, science, and technology.

Dr. Huntoon continued his discussion in 1967:

"Our National Measurement System is one of a number of mutually interacting systems

within our technologically based society that form the environment in which the

individual citizen must live and function. Familiar examples are the communication, transportation, educational, medical and legal systems, all of which may

be included under the general heading of social systems."

"In view of the demonstrated value of the systems approach for the understanding and

improvement of hardware such as computers and weapons, some of these social systems

, are being subjected to the same type of analysis. The National Measurement System,

which evolved in this country with little formal recognition as a system, is now

being examined in this way at the National Bureau of Standards (NBS) which undertook the study of the National Measurement System partly because of the all -pervasive nature and great economic importance of the nation's measurement activities,

and partly because of the challenge to NBS in putting its splendid new facilities

to optimutp use for the benefit of the nation. Such optimum use can be approached

only when the National Measurement System, of which NBS is a central element, and

the services it requires for effective operation are sufficiently well understood."

Over the years both before and since 1967, NBS has taken a number of approaches to the study of our national system for physical measurements. The current series of

studies was initiated in 1972 by Dr. Ernest Ambler, then Dr. Huntoon 's successor as Director of the NBS Institute for Basic Standards, now Acting Director of the Bureau. The reports of these studies are being presented to the public at large for the pur- pose of increasing national understanding, and the operational effectiveness, of our

National Measurement System. They are presented as an intial or interim, not final,

word on the subject. NBS welcomes contributions from all sectors of the System

which can aid it in increasing its understanding of and effectiveness in supporting

that System,

iii
i

I

NOTICE

A diligent effort has been made to make this

report comprehensive and accurate as of March

1975. Since that time no important changes or additions have been made. There have, however,

been a few significant changes in the National

Measurement System for Time and Frequency. The

interested reader may wish to contact the author

for his opinions on these changes.
CONTENTS

Page

EXECUTIVE SUMMARY 1

1. INTRODUCTION 3

2. STRUCTURE OF THE MEASUREMENT SYSTEM 3

2.1 Conceptual System 3 2.2 Basic Technical Infrastructure 4

2.2.1 Documentary Specification System 4 2.2.2 Instrumentation System 4 2.2.3 Reference Data 7 2.2.4 Reference Material 7 2.2.5 Science and People 7

2.3 Realized Measurement Capabilities '. 8 2.4 Dissemination and Enforcement Network 13

2.4.1 Central Standards Authorities 13 2.4.2 State and Local Offices of Weights and Measures 13

2.4.3 Standards and Testing Laboratories and Services 14 2.4.4 Regulatory Agencies 14

2.5 Direct Measurement Transactions Matrix 14

2.5.1 Analysis of Suppliers and Users 15 2.5.2 Highlights Major Users 22

3. IMPACT, STATUS AND TRENDS OF MEASUREMENT SYSTEM 27

3.1 Impact of Measurements 27

3.1.1 Functional, Technological and Scientific Applications.. 27 3.1.2 Economic Impacts - Costs and Benefits 28

3.1.3 Social, Human, Man-on-the-Street Impacts 30

3.2 Status and Trends of the System 30

4. SURVEY OF NBS SERVICES 34

4.1 The Past 34

4.1.1 Developments up to 1923 34

4. 1. 2 Frequency and Time Standard Development in the

Period 1923 to 1947 35

4.1, 3 Atomic Standards and Further Improvements in the

Broadcast Services 36

4.2 The Present - Scope of NBS Services 38

4.2.1 Description of NBS Services 38

4.2.2 Users of NBS Services 41 4.2.3 Alternate Sources 44

4.2.4 Funding Sources for NBS Services 46

4.2.5 Mechanism for Supplying Services 46

4.3 Impact of NBS Services 46

4.3.1 Economic Impact of Major User Classes 46

4.3.2 Technological Impact of Services 46

4.3.3 Pay-off from Changes in NBS Services 46

V
Page

4.4 Evaluation of NBS Programs 46

4. 5 The Future. • 46

5. SUMMARY AND CONCLUSIONS 48

APPENDIX A. METHODOLOGY OF THE STUDY 5 0-62

REFERENCES 63-65

LIST OF FIGURES

Figure 1. Historical Development of Time Keeping Accuracy 5

Figure 2. General Time-Domain Behavior of Oscillators 10

Figure 3. Time-Domain Behavior Typical of Several Types of Oscillators. 10

Figure 4. Development of Frequency Accuracy in the FDM System of the

Telephone Industry 23

Figure 5. Responses to Set 1 of the Delphi Questionnaire 32

Figure 6. Time-Domain Behavior of NBS Sources and Measurement System... 40

Figure 7. Frequency-Domain Behavior of NBS Sources and Measurement

System 40

Figure 8. Calling Rate for NBS Time-of-Day Service (303-499-7111 )... 44

LIST OF TABLES

Table 1. Instrumentation Hierarchy for Coordination of Frequency 6

Table 2. Instrumentation Hierarchy for Coordination of Time 7

Table 3. Characteristics of the Major T&F Dissemination Systems 12

Table 4. T&F Flow Matrix 17 _ Table 5. Relative Use of WWV/VH Services (12,000 Respondees) 42

Table 6. Adequacy of WWV/VH Services to Various Users 43

Table 7. Distribution of Respondents by Principal Use 43

vi
ABSTRACT

The results of a study of the National Measurement System for

Time and Frequency are given. The system is viewed from three

vantage points: (1) The Instrumentation that provides sources of

time and frequency (T&F). (2) The Suppliers and Users of T&F.

(3) The Calibration hierarchies for T&F sources. An attempt is made to determine the technological, scientific, economic, and

social effects of the system. Predictions are made about possible

important changes in the system. The past, present, and possible

future positions of NBS in the system is described in detail.

Keywords; Atomic frequency standards; aviation industry; electric

power industry; national measurement system, position location'

shipping and boating industries; standards laboratories; telephone

industry and specialized carriers; time and frequency; time

scales; users of NBS radio broadcasts.

vii

THE NATIONAL MEASUREMENT SYSTEM

FOR TIME AND FREQUENCY

Allan S. Risley

Time and Frequency Division

Institute for Basic Standards

EXECUTIVE SUMMARY

The major purpose in studying the National

Measurement System for Time and Frequency was

to determine who uses time and frequency, how

they use them, and what their use means to society.

The system is viewed from three vantage

points:

1. The instrumentation that provides

sources of time and frequency (T&F).

2. The suppliers and users of T&F.

3. The calibration hierarchies for T&F

sources.

Most of the work of this study went into

determining the present status of the system.

Historical information was, however, helpful

in forecasts of the future and in putting

NBS T&F activities into perspective.

Instrumentation . The major types of instrumentation which have served as sources of

time and/or frequency over the last 75 years

are pendulums, tuning forks, quartz oscillators, and atomic oscillators. Quartz and

atomic oscillators are the sources of primary

importance today.

The characteristics of precision quartz

oscillators, superconducting cavity oscillators, and the major atomic oscillators are

given, and some of their areas of application

are described. For example, atomic oscillators are shown to be an increasingly impor- tant part of the telephone industry and basic

science. The National Bureau of Standards

has been a central element in the research

and development of atomic T&F standards

throughout the some 25-year history of these

standards. The Bureau has also made some

basic contributions to the development of

precision quartz oscillators.

Suppliers and Users . A compact description

of fourteen basic supplier-user categories is given in matrix form. The relationship be- tween a given supplier and user is specified

by two descriptors. One descriptor gives the

volume of use of a specified time or frequency output. The other gives the impor - tance (to an organization's internal operations) of that output.

The majority of the effort devoted to this

study of the National Measurement System for

Time and Frequency went into extensive

studies of eight major areas. They are:

- Standards Laboratories

- Users of NBS Radio Broadcasts

- Telephone Industry and Specialized

Carriers

- Military

- Position Location

- Aviation Industry

- Electric Power Industry

- Shipping and Boating Industries

Information gathered in these studies was

vital in completing major portions of the T&F flow matrix. The communication and position location industries emerge as two of the

most important and sophisticated users of

T&F. The matrix indicates the great impor- tance of the NBS standard T&F broadcasts. A current study is increasing our understanding

of the users of stations WWV and WWVH. The

study confirms that the applications of

communications, navigation, and standards

laboratories are very important. The three most heavily used aspects of our broadcast

services are voice announcements of time-ofday, one-second "ticks", and standard frequencies.

Calibration Hierarchies . The various

sources of time and frequency must be compatible with one another to within some specified tolerance. The stringency of this re- quirement depends on the sources involved and

the uses to which they are to be put. The

necessary compatibility is often achieved by means of a calibration hierarchy.

There is no legal, technical, or economic

force to create a unified calibration hierarchy, and none exists. This is one reason why it is difficult to comprehend the

National Measurement System for Time and Fre- quency. Multiple hierarchies do exist, how- ever, and they are basic to the system. Some

of these hierarchies have the force of law

and apply across organizational boundaries.

Others are voluntary or are only binding

within one organization. Those not having

the force of law usually have the greatest

requirements for quality of T&F. To understand why these several hierarchies exist, it

is essential to consider cost and ease-of-use

as wel 1 as qual ity

.
Four major calibration hierarchies are those of the standards laboratories (industrial, governmental, etc.), telephone timeof-day, the military, and the telephone

industry. The National Bureau of Standards

has been a part of these four hierarchies.

It is presently a fundamental part of the

standards laboratory hierarchy and telephone

time-of-day. It is also an important part

of the military T&F calibration system.

The National Bureau of Standards' importance

to the telephone industry is much less than

it was in the past (since the telephone

industry is now basing its synchronization

on atomic oscillators), but is potentially

still important.

The Future . The system appears to be

changing in three major ways:

1. ) By 1980-85 there will probably be a widespread, low-cost network of

clocks that are synchronized in the

range of 1 to 10 ys. Today, widespread synchronization, at a cost of

a few hundred dollars per site, can only be done to about 1 ms.

2. ) By 1980-85 the market for frequency

equal izati95 in the range 1 x 10"

to 1 X 10" will probably be quite

important. The cost per site will

need to be less than about $2000 (in

1975 dollars), and the equipment must

be easy to use.

3. ) The use of quartz watches and clocks,

with digital readouts and the capability of being set to the precise

second, will probably be extensive.

This may necessitate a widespread

calibration network for time-of-day

that is accurate to about 0.1 seconds.

The Time and Frequency Division of NBS currently has two programs - T&F dissemination via satellite, and frequency calibration

via TV - that address the first two areas

of probable change. A third program directed

to these frequency equalization requirements,

a low-cost, medium-accuracy oscillator, will

likely begin soon.

The third area of probable change, if it occurs, will be more of an economic than a technical problem. As such, it would not likely increase the demand for NBS resources with regard to time-of-day.

Conclusions . This study of the National

Measurement System for Time and Frequency

clearly demonstrates that NBS has an important and unique role in the system. The

question is not whether there are desirable

alternative sources for the services presently rendered, or whether these services are in

fact needed. It is instead whether NBS can perform its function more economically and

effectively. Experimental broadcasts of

standard T&F via satellite and other developments indicate that it can do both.

The NBS T&F services have been, and are, and should be, in the nature of what econo- mists call a "collective good". This is a "good" (product) which is clearly of social

value but one for which a fair market price

is difficult to determine. It is interesting

to note however, that there is now a mi nimum

of one million dollars worth of special

purpose receiving equipment in the field.

This equipment was specifically designed to receive the broadcasts of WWV and WWVH or WWVB. Also, if $0.05 per call were received

for the NBS telephone time-of-day service

this would generate a revenue of $50,000 per year.

One of the most general things that

emerges from the entire study is that time - and its ever-present companion, frequency - are the great coordinators, the great organizers. Almost any activity today that

requires precision control and organization

rests on time and frequency technology.

(A diligent effort has been made to make

this report comprehensive and accurate as of

March, 1975. Since that time no important

changes or additions have been, made. There

have, however, been a fevy significant changes

in the National Measurement System for Time

and Frequency. The interested reader may

wish to contact the author for his opinions

on these changes.

)

2
THE NATIONAL MEASUREMENT SYSTEM

FOR TIME AND FREQUENCY

"One generation passeth away, and another cometh; but

the earth abideth forever.

The sun also ariseth, and the sun goeth down, and hasteth

to the place where he arose." Ecclesiastes 1:4,5

1. INTRODUCTION

Time is the great organizer. It organizes

the activities of people and those of machines. People get up by it and go to work

by it. It is the analog of work and a measure of value. For machines, time scales

permit the time ordering of a sequence of

events and facilitate the simultaneity of

events. Good frequency control, which is a fundamental aspect of time keeping, is essential to almost all communications.

Time interval, or its reciprocal, frequency, can be produced more precisely and

measured more accurately than any other

physical quantity. It can be measured about

four orders of magnitude more accurately

than length, the next most accurately measurable physical quantity.

Time and Frequency (T&F) are unique among

the physical quantities in that they can be

transmitted by electromagnetic (EM) radiation. Frequency is an intrinsic property of

every EM wave. Thus, if a transmitter is controlled in its frequency by a frequency

standard, the frequency of that standard can

be transferred widely as an EM wave. If the

transmitter is controlled by a time standard

(i.e. in phase as well as frequency) then

the time of that standard can also be trans- ferred as an EM wave. Another property of T&F that may be unique

is that for almost all users, sources are commercially available which are as good or better than needed. This does not mean

however, that it is always economic to use what is technically desirable.

This report is based on a study whose

purpose was to gain a broad understanding of

the National Measurement System for Time and

Frequency. It describes the concepts and

the instrumentation upon which the system is based, and the flows of T&F equipment and

services between those institutions which

are the suppliers of T&F and those that are

the users. General conclusions are drawn

about who the major users are and what the

primary functions are that T&F performs for

them.

The report discusses significant changes

in the National Measurement System for Time

and Frequency which appear to be occurring,

and an attempt is made to give a "feeling"

for the economic dimensions of T&F in U. S. society. Finally, the position of the Time

and Frequency Division of NBS in the total

system is examined, with present NBS services

and possible non-NBS alternatives described.

2. STRUCTURE UF THE MEASUREMENT SYSTEM

2.1 Conceptual System

Time interval is one of the seven base

units of the present International System of

Units of Measurement (SI). The SI unit of

time interval is the second. Frequency,

which is dimensional ly the reciprocal of time

interval, is a derived unit in the SI system.

The unit of frequency is the hertz. The

frequency of a sinusoidal signal whose period

is one second is one hertz.

It is important to understand the relationship between date and time interval. Date is an accumulation of time intervals beginning

at a specific, and arbitrary origin. Historically, these intervals were based on the

motion of the earth with respect to other

celestial bodies. Prior to 1956, the second

was defined as the fraction 1/(86,400) of a mean solar day; from 1956 to 1967, it was

the ephemeris second defined as the fraction

1/(31,556,925.9747) of the tropical year at OOhOOmOOs 31 December 1899, and since 1967,

in terms of a resonance of the cesium atom. The present definition of the second states,

"The second is the duration of 9,192,631,770

periods of the radiation corresponding to the transition between the two hyperfine

levels of the ground state of the cesium-133

atom." [13th CGPM (1967), Resolution 1] A very important change occurred when, in 1967, the second was defined in terms of an atomic transition. A very much more uniform

time scale is generated by a cesium time

standard than by the motion of the earth.

Thus, the time interval between two events may not be accurately given by the difference

between two dates [1]. Nevertheless, there

is a practical reason for maintaining two types of time scales. Some people, such as navigators, must have a scale based on the

earth's motion, whereas there are important

technological and scientific applications

based on the uniformity of an atomic scale.

It is useful to take a very general look
at the functions that T&F standards can perform. Because a time standard always contains a frequency standard as an integral

part of its mechanism, I will only use the

term "time standard" in discussing these

functions. Examined from a general basis of

its inherent capability, there seem to be

three basic functions a time standard can perform:

1. Set a Pace . This is the constant frequency (rate) feature. It applies

to those who need only frequency and

not phase. A basic application of

this function would be in dividing up "frequency space" for Frequency Division Multiplexing in telecommunications , 2. Uniform Time Scale . A time standard

provides a uniform time scale. It

is useful to divide this category

into three sub-categories:

a. Label ing . The scale can be used

to label events so that their

order of occurence in time can be

recorded. If desired, this re- cording can yield the time interval between any two events. From

a practical point of view, the

labeling function employs a time

scale that runs uninterrupted for

long periods of time. Date is a good example.

b. Start-Stop . This feature of a time scale, when the scale is available at more than one geo- graphical location, allows events

to be begun or concluded simultaneously. One basic application is

in dividing up "time space" for

Time Division Multiplexing in

tel ecommuni cati ons

.

c. Time Interval . In principle, the

measurement of all time intervals

falls under the sub-category of

labeling. There are, however, a great many needs for the accurate

measurement of short time intervals. These needs are usually met

by time scales that run for only

short periods of time. Thus, the user tends to obtain item (a) by

different means than item (c) and

it is useful to distinguish between

the two.

3. Distance vs. Speed . A uniform time

scale can be used in conjunction with

the constancy of the speed of light

to determine the distance between

points that are spatially separated.

It is a basic technique in position

location.

2.2 Basic Technical Infrastructure

The word "system" in the phrase National

Measurement System, might be taken to mean a very high degree of organization. For ex- ample, an extent of organization which

transcends individual institutions, permeates

the entire structure and, perhaps, has the

force of law. The National Measurement

System for Time and Frequency does not possess this degree of organization, and this

is one reason that the system is difficult

to understand, or even to describe.

In the National Measurement System for

Time and Frequency, there are some regulations which have the force of law but they

impose tolerances which are very lax compared

to the state-of-the-art. The fractional

accuracies imposed on time, and fre- •quency lie in the range 10"^ to 10'^. Fractional error is the ratio of the estimated

error in frequency (time) to the nominal

frequency (elapsed time).) The organizations which create and enforce these

rules and the functions to which they apply

are discussed in section 2.4. On the other hand, there are important

parts of the system where tolerances are much

tighter. These tolerances are required in

order to satisfy the function to which T&F

is being applied and tend to be limited to specific institutions and/or functions.

Examples are given in sections 2.5.1.2.3, 3,

and 4.

2.2.1 Documentary Specification System

Documentary standardization activities

in the field of time and frequency are very

limited. Those that do occur are associated

with the physical standards authorities,

offices of weights and measures, and regu- latory agencies; and are thus best discussed

in sections 2.4.1, 2.4.2, and 2.4.4 below.

2.2.2 Instrumentation System: Measurement

Tools and Techniques and the Instru- mentation Industry

Figure 1 displays the historical development of accuracy in time keeping devices.

Today, a few primary frequency standards

based on the cesium atom (see sec. 2.1) form - the most accurate physical realization of the

definition of time interval. A primary frequency standard is a device which is spe- cifically constructed to permit the evaluation

of the major factors which cause the output

of the device to deviate from the definition.

4
At present, the three most accurate primary

frequency standards known have each ^|monstrated an accuracy of about 1 x 10" . These

devices were developed and are operated by

the Physi kal ish-Technische Bundesanstalt

(PTB) in West Germany, the National Research

Council (NRC) in Canada, and the National Bureau of Standards (NBS) in the United

States [2]. These three devices provide, in

principle, the best sources of calibration

for those other devices needing frequency

accuracy , either for its own sake or for

establishing an accurate time scale.

Tables 1 and 2 list, from the point of

view of accuracy and long-term stability (see

sec. 2.3 for definitions), a hierarchy of

instruments for generating frequency and

time. In some cases the instruments are intended primarily for end-use, but in other

cases the instrument may serve either the

end-use or to calibrate an instrument of

lesser quality. By "end-use" I mean the use

of time or frequency for an important socioeconomic function. An example would be the use of an atomic frequency standard for

stabilizing the carrier of a TV transmitter.

As a further example, quartz and atomic

sources often serve both for end-use and for

q:o

C_3 a:

1 ns r

10

1 00

lys

1 0

1 00

1 ms

1 0

1 00

Is

10

10^

10^

10^

NOTES: 1.) INTENT IS TO SHOW BENCHMARKS OF PROGRESS. VARIOUS

CLOCK TYPES CAN SHOW IMPROVED

ACCURACIES

2. ) PRIOR TO 1 000 A. D. VARIED

TIMEKEEPERS WERE USED

SUCH AS MECHANICAL

WATER CLOCKS, NOCTURNIALS,

SUNDIALS, TIME CANDLES,

ETC. , OF LITTLE KNOWN

ACCURACY.

CESIUM

ATOMIC I IMPROVED •

NBS III) /

CESIUM

ATOMIC

(NBS-5 EST)

CESIUM

ATOMIC

(NBS III)

FIRST ATOMIC.

CLOCK( 1 949)

FREE PENDULUM

(SHORTT)

BAROMETRIC

COMPENSATION

(ROBINSON)

• IMPROVED ESCAPEMENT

(GRAHAM)

1 HR

\

VERGE & FOLIOT

BALANCE CLOCKS

J I \ L

CROSS-BEAT

ESCAPEMENT

(BURGI)

1973

1 000 1200 1400 1600 1 800

CALENDAR YEARS, A.D.

Figure 1. Historical development of timekeeping accuracy

2000
calibration of lower quality sources. There

is another way of looking at tables 1 and 2: Frequency and time are used for various social and technological functions. In order

to accomplish these functions the various

instruments (sources) must be coordinated

one with another. For example, two sources

of frequency which nominally claim to be

equal must, in fact, be equal to within a

specified tolerance. The same holds true

for sources of time. Table 1 describes the

most important types of devices for generating

frequency. It gives, in column 2, the accuracy or precision to which it is useful to equalize their frequencies. It also gives in column 3, means by which this equalization can

be achieved. Table 2 gives the same informaTable 1. Instrumentation hierarchy for coordination of frequency

Source of [commercially

available] Frequency

Accuracy of Coordination

Needed (Fractional)

Coordination: Means of

Calibration

Tuning Forks 1 X 10"^ to 1 X 10"^ Commercial frequency counter; standard broadcasts

Electric Power Generators

-5 a2 X 10

(1 X lO'-^ Hz in 50 Hz)

Commercial frequency counter

or standard broadcasts

Quartz Oscillators 1 X lO"'' to 1 X 10' 10 Commercial frequency counter

up to 1 X 10"^; free-running

atomic oscillators or standard

broadcasts for 1 x 10"^

or better

Atomic Oscillators 1 X 10'^ to 1 X 10"^^ Commercial cesium standards,

hydrogen masers and national

primary standards. Rubidium

oscillators can be calibrated

on site with a commercial

cesium standard or a hydrogen maser to an accuracy of about

-12

5 X 10 . For calibration

at a distance, use these same sources and 1 ine-of-sight

microwave or an LF or VLF broadcast. For frequency

equalization in the range of

5 X 10"^^ to 1 X 10"^^,

compare to a national primary

standard and use on-site

calibration or LF or VLF broadcasts

6
tion for the major types of time sources. The reader who is interested in details of T&F calibration should consult reference 3. The following will give some idea of the

activity in the manufacture and use of some

of these instruments:

The worldwide sales volume last year in the watch industry was about four billion

dollars, and a total of about 200 million

watches were sold.

The- total number of cesium and rubidium

standards in use (this includes those used

as clocks as well as those that serve just

as frequency sources) is about 4,000 to

6,000. The number of units sold last year

was about 1,000. These units were produced

by about seven companies and the sales volume

was approximately 12 million dollars.

The total number of quartz oscillators in the field and produced per year is vastly

greater than the atomic variety. For example,

many TV sets use a quartz oscillator. If we confine ourselves to precision quartz

oscillators (free-^-unning drift rate of not worse than 1 x 10" /day) then about eight

major U. S. firms sold about 10,000 units

in 1974 in the U. S. The corresponding

dollar volume was about $10 million.

2.2.3 and 2.2.4 Reference Data and Reference

Materials

Reference data and materials are not of

significant separate importance in this field

of measurement.

2.2.5 Science and People

Most of the people who use T&F use it as

a component part of some other technology.

For example, frequency standards provide the

carriers for the frequency-division-multiplexing system of the telephone industry.

This "other" technology - and not T&F - is the major business of most of these people.

Thus, although we may know a lot about the

needs of "their" technology, we generally

don't know much about them. For example, we

don't know much about their educational level

or how much of their time they spend "directly" on T&F matters.

We do, however, know more about people

Table 2. Instrumentation hierarchy for coordination of tinne

Coordination of Time

Source of Accuracy of Coordination Coordination: Means of

Time Needed Cal i bra tion

Regular (escapement) 10 sec « 1 X lO-^day Telephone time from NBS or Watches and clocks [10 times better than certain select cities;

usual watch] Standard radio broadcasts

Electric Clocks 1 sec « 1 X 10"^ /day Telephone time from NBS or

[More accurate than most certain select cities;

power companies can hold] Standard radio broadcasts

Quartz Watches and clocks 0.1 sec « 1 X 10"^/day Telephone time from NBS or [stability this good but certain select cities; can't be set this well] Standard radio broadcasts

Precision Quartz Clocks 1 ys a 1 X 10"^°/day Cesium clock: Standard radio

[Quartz not commonly used broadcasts

as time scale]

Atomic Clocks

_3 From 3 X 10 sec to NBS or USNO time scales via

- 6 «3 X 10 sec on yearly portable clock or LF or VLF

bas i s broadcasts

[i.e., 1 X to 1 X 10'^^]

7
whose major business is, or is strongly re- lated to, developing primary T&F standards.

The National Bureau of Standards estimates

that there are currently about 180 people

with formal academic degrees (or equivalent

experience) who spend most of their time in

this work, with the bulk of these people

working in foreign laboratories and about

five percent of the total in the T&F Division

of NBS. This activity is contained in ten scientific areas:

% of Total Area Effort

- Primary Cesium Standards 7%

- Other Cesium Design and

Development 5%

- Atomic Time Scales 19%

- Hydrogen Devices 20%

- Saturated Absorption 12%

- Ion Storage 6%

- Rubidium Devices 11%

- Superconducting Cavity 2%

- Infrared Frequency Synthesis 7%

- Other Devices 10%

There are no known professional societies

primarily devoted to frequency and time

standards.

There are two meetings, held on an annual

basis, and devoted to the subject of T&F. They are the Symposium on Frequency Control

sponsored by the U. S. Army Electronic

Command, and the Precise Time and Time Interval Planning Meeting sponsored by the U. S. Naval Electronic Systems Command, NASA

Goddard Space Flight Center, and the U. S. Naval Observatory. Each conference publishes

a Proceedings.

In addition to these two Proceedings,

several other publications contain an important amount of information: 1.) the

Proceedings of the Conference on Precision

Electromagnetic Measurements (sponsored by

NBS, the Institute of Electrical and Electronic Engineers (IEEE), and the International

Scientific Radio Union), 2.) the IEEE Trans- actions on Instrumentation and Measurement,

3.) Metrologia (published by SpringerVerlag), and 4.) the Proceedings of the

IEEE.The personnel of the T&F Division of the

NBS publish a great deal of information about

T&F. Some of this appears in the abovementioned journals and a great deal more

appears in official NBS publications. In the last five years, more than 70 publications on T&F have been produced by NBS per- sonnel. Three of the most general of these

are referenced [1, 3, 4] in this report. In addition to these, the NBS occasionally conducts courses on various aspects of T&F.

It is also important to note that there are several educational institutions actively

involved in T&F matters. Major ones are: Harvard University, Massachusetts Institute

of Technology, Johns Hopkins University,

Columbia University, Stanford University,

Laval University (Canada), University of

Paris (France), University of Tokyo (Japan),

and the University of Mainz (Germany).

2.3 Realized Measurement Capabilities

In discussing the measurement capabilities

of the National Measurement System for Time

and Frequency, the system would be easier to understand if there were one instnanent that was the ultimate standard for T&F. Following

the ultimate standard in this hypothetical

scheme would be several instruments - all identical to one another - and each of these

would be calibrated by the ultimate standard.

The system would have further levels, each

instrument in a given level, being identical.

As the quality of the levels decreased the

number of instruments in a given level might

increase. Any instrument in any given level

would be calibrated by an instrument in the

next superior level. Thus, each instrument

in the entire system would be calibrated to

a degree |:hat was commensurate with its

innate quality and each would be traceable to the ultimate standard. At each level of

this hypothetical, pyramidal structure there

would be end-users, those people who use time

or frequency to perform some "socially useful"

function. And each user would enter the

system at that level which best met his

technical needs

.

This is not an adequate description of

the National Measurement System for Time and

Frequency. The reasons it is not are twofold. First, both time and frequency are multidimensional quantities. One user badly

needs one aspect while another needs some other dimension. Second, the costs and

benefits of a given time or frequency input

will vary greatly from user to user. Thus,

different users will purchase different inputs although from a technical point of view

the highest quality input would serve them

all. A description of the measurement capa- bilities of the system requires an approach

from several directions. I will begin by

discussing several aspects - accuracy, sta- bility, and precision - of the quality of a time or frequency source. These terms will

be defined and some aspects of the quality

of the major sources of T&F will be given.

In enumerating the sources of T&F it is necessary to talk about both the generators

of T&F and about dissemination of their

8
signals to the user. Finally, an instrument

hierarchy does exist in the system and is displayed in tables 1 and 2. The reader who is not familiar with the

technical details of T&F may wish to skip

some of the section on stability.

The quality of a frequency or a time standard cannot be described by a single number.

In fact, the quality of a standard may depend quite strongly upon the use to which it

will be put. Even when the situation is re- stricted by asking "How good is this standard

when used for the following purpose? as opposed to "How good is this standard?" it is often necessary to make more than one meas- urement to adequately characterize the

standard. There are three terms which are typically associated with the quality of T&F standards defined as follows:

Whenever the measurement of anything is discussed it is quite common to find the

word aaauracy used and, often, misused. A commonly accepted definition of accuracy is "the degree of conformity of a measured and/

or calculated value to some specified value

or definition." Thus, the currently accepted

definition of the accuracy of time interval

(frequency) is that given in section 2.1. A

physical realization of the definition of

frequency accuracy requires a device whose

working substance is atoms of cesium. In addition, the device, usually referred to as

a primary frequency standard, is specifically

constructed to permit the evaluation of the

major factors which cause the output of the

device to deviate from the definition. Be- cause these devices are very expensive and

complex, very few of them exist. Section

2.2.2 mentions the three primary standards

which currently exhibit the best performance.

To gain insight into the difficulties of

determining the accuracy of a primary standard

the reader should consult reference 5. The

term "accuracy" need not be restricted to primary frequency standards; any frequency

standard whose frequency has been measured

with respect to a primary standard, and

which has adequate stability, can have its

accuracy specified.

Stability is a term used in characterizing

both frequency and time standards. Intuitively, the frequency stability of an oscillator

is the degree to which its output is a pure

sinusoid. Conversely, the frequency instability of an oscillator is the degree to which

its output deviates from that of a pure

sinusoid. What is needed is a parameter

which measures the deviation of the output

from this ideal. Although there is no single

universally accepted measure of frequency (or

time) stability, there are two measures of

frequency stability that are in wide use. A

very brief discussion of these two measures

is given below. The reader should consult

references 6 and 7 for additional details.

The two frequency stability measures are based on^a quantity y(t) defined by

y(t) = where vo is the nominal fre2ttvo quency of the output and $(t) is the time

derivative of the instantaneous phase of the

output. The deviations of the output from

the sinusoidal ideal are contained in the

quantity ij>(t). Thus, y(t) represents the

instantaneous fractional frequency deviation

of the signal from its nominal frequency, vq . The first frequency stability measure is Sy(f), where y is the quantity just defined

and f is the frequency of one of the spectral

components of the output. The quantity Sy(f)

is known as the spectral density of the

instantaneous fractional frequency fluctuations, y(t)

The second frequency stability measure,

cJy(T), depends on a number of variables, one

of which is the time duration of a single

measurement, x. '^y(T) is known as the Allan

variance of the fractional frequency fluctuations, y(t)

Without going into great detail about the

quantities S (f) and aJx) some qualitative

y

statements can be made. In practice, the

frequency- domain measure, ^^(f), is used

when the spectral content of most of the

fluctuations of interest is at frequencies

of a few hertz and higher. The practical

application for the time-domain measure,

Oy(T), is for those signals whose fluctuations

are at frequencies of about one hertz and

less (i.e., whose periods are about one second and longer). For example, if a frequency standard is being examined for its

possible application in Doppler radar, measurements of Sy(f) would be appropriate. If,

however, the frequency standard is to be used

as a clock, measurements of would be

needed. Note that many measurements must be

made for an adequate characterization of

stability, which is true whether it is Sy(f) or ^yii) which is being measured. The reason is that S (f) and ''y(T) do vary with

y ^ f and T respectively. Figure 2 shows a plot

of cJy(T) that is' typical of many frequency

standards. For the major economic applications of T&F, attention should be paid to the fluctuations whose periods are about one

second and longer. If these requirements are satisfied, then the requirements for "shortterm" stability (periods less than about one

second) are usually also satisfied. In this

9
report, therefore, I generally refer to stability in terms of 0^(1).

I. ~ t"' white or flicker of phase noise

II a ~ t""^ white frequency NOISE

II. o = CONSTANT FLICKER "FLOOR" (FLICKER OF

^ FREQUENCY)

III. 0 ~ T° 0 < a < I TYPICAL

TIME T

Figure 2. General time-domain

behavior of oscillators

The subject of frequency and time stability is closely associated with the subject

of electrical noise. For any given oscillator there is some oyfx versus t (or

o-y(T) display. This curve could be explained

in terms of additive and multiplicative

noise. When the signal of a frequency gen- erator or a time scale is to be disseminated

to some other site, the noise properties of

the dissemination mechanism degrade the

signal [8]. It is sufficient to note here

that a aJT) versus x curve can be measured

at the user's site, i.e., after the signal

has been disseminated. Thus, the noise

effects of both the source and the dissemination means are included.

The third term is precision, a word used

commonly in referring to measurement quality

which must be clearly distinguished from

accuracy. Precision is the repeatibil ity of

a given measurement under a specified set of

conditions. Many repetitions of a given

measurement will produce a series of values

and the scatter of these values is a measure

of the precision of the measurement. One

particularly good measure of frequency precision is aJx). If a set of measurements

contains a systematic error, then the precision of the measurement is better than its

accuracy. In the limit of no systematic

errors, a measure of precision is identical

to that of accuracy (as described by the measure in use).

I will be using two other terms: frequency equalization and time synchronization.

The discussion of accuracy and stability

permits some additional understanding of

these two areas. For example, if I have two oscillators that have a fractional frequency

accuracy of 1 x 10"^^ then, by definition,

they are equal in frequency to about

n/Tx 10"^^ Thus, I have that level of frequency equalization without setting up a dissemination system to actually set one oscillator equal to the other. A claim to accuracy is a very strong claim - one which

requires a great deal of careful measurement

experience. Without such experience, adequately documented, the users' confidence is justifiably low.

Figure 3, which gives some understanding

of the practical importance of knowing an oscillator's frequency, is a display of

ay(T) versus x for typical atomic oscillators

of various types. If a person needs good

stability over a period of months (maybe even

a few years) and doesn't want to calibrate

frequently, he will probably need a cesium

beam oscillator. But, if he has a network

of such oscillators and needs to have them

equal in frequency to about 1 x 10'^^, then

the inherent stability (instability) of the

oscillators (see the curve labeled commercial Cs in fig. 3) will require that they

be compared with each other for about 10^ seconds or longer. That is, measurements of

adequate quality take time. This can be seen from the first parts of the curves

(labeled I) in figures 2 and 3. It can be seen that the quality of comparison improves

with averaging time up to the point of the

break in the curve.

t(s) Figure 3. Time-domain behavior typical

of several types of oscillators

Consider the flat part of the curves - that which is labeled II in figure 2. This

points out that, beyond a certain averaging

time, that given by the break point between

regions I and II, it is useless to average

longer. A practical example of this brings me back to the network of cesium oscillators

to be frequency equalized to a few parts in 10^^. Figure 3 indicates that by averaging

for about 10^ seconds or longer this equalization could be obtained and, in fact, if

the averaging were done for 10^ seconds

(about one day), they could be equalized to

10
about 1 X 10"^ ^ But, as a practical

matter, such a group of oscillators would be

interconnected by a dissemination system.

Any dissemination system has a stability

(noise) behavior similar to the curves of

figures 2 and 3. One dissemination system of great practical importance is the line-of -sight microwave system, owned and operated by the

American Telephone and Telegraph Company,

the NBS has made extensive studies of the

frequency stability of this system. Our present estimate is that it reaches the

flat portion (the flicker-of frequency portion) of its ay(T) versus t curve at a level of about 2 x 10" for an averaging

time of about one week (about 6 x 10^ seconds). This indicates that no matter

how good the oscillators are, if they are

to be frequency equalized by this dissemination system, they cannot be equalized

to better than about 2 x 10"^^

For time synchronization, the story is essentially the same. To synchronize the

"ticks" of one time scale with respect to another takes time. As the averaging time

(measurement time) increases the synchronization improves until the point where no further improvement is obtained. In practical cases it is usually the dissemination

system that produces the limitation.

The quality of the major sources of T&F

and of the major means of disseminating T&F are presented below.

Figure 3 gives the stability performance

of the major types of frequency standards.

Note that there are two non-atomic standards

shown. The precision quartz crystal oscillator (Xtal) shows excellent performance in

short-term, but suffers from drift in longer

term. The best quartz crystal oscillators

have a drift rate of about 1 x lO'^Vday.

The superconducting-cavity oscillator (SCC

OSC) has the lowest "flicker" level of any

known device. Its stability in long-term

has not, as yet, received adequate study.

Cesium beam standards have the best demonstrated long-term stability. Typical

commercial cesium beam standards have demonstrated the ability to hold their frequency

to a few parts in 10^^ over a period of a year. Because of this long-term stability, most time scales are based on cesium frequency standards. The stability of a time

scale, over a specified averaging time, and

based on a specific type of standard, can

be estimated from figure 3. Accuracy is presently defined in terms

of the cesium atom, and at the present

state-of-the-art of primary standards this

is proper. The reasons are that the cesium

device has the best demonstrated ability for

evaluation of systematic errors, the precision with which measurements of its frequency can be made is very good, and it has the best demonstrated long-term stability.

It may well be, however, that some other type

of device will be developed to the point

where its accuracy capability is better than

that of the cesium beam device. If this is so, then given enough experience with this

type of device - and presuming that its

"working substance" is some other atom (or

molecule) - the definition will probably be

chanqed.

One last comment about accuracy: a great

deal of experience has been gained with

commercial cesium beam devices. Many of them

have been built and in operation for long

periods of time, and primary standards have

been available for comparisons. Because of

this, a great deal of confidence has been

developed about their accuracy. It can be

said, with a rather high degree of confidence,

that any given commercial cesium beam is accurate to about 1 x 10-'". (This statement

presumes that the standard meets a few selfcontained performance checks.)

Table 3 displays some basic features of

the major frequency and time dissemination

systems. One of the main things to be noted

is that the performance of any given system,

just as any given oscillator, usually cannot

be characterized by a single number. For example, the performance of the Loran C system depends very strongly on whether the user is primarily receiving the ground wave

or the sky wave. A description of the detailed performance of each system and the

various pros and cons of their use is beyond

the scope of this report. The reader who

desires to pursue the subject in greater detail can find more information in reference 8. The reader can now return to tables 1 and

2 and re-examine the hierarchy of instrumentation. In this re-examination, one can- not help but wonder what trade-offs - in

accuracy, stability, cost and ease of use - exist at the various levels. Although I cannot hope to answer this question with

completeness (and certainly not with finality)

partial answers will be found throughout the rest of this report.

Hhe reader who wishes to learn more about

the state-of-the-art of primary frequency

standards should see reference 9.

11
Table 3. Characteristics of the major

T&F dissemination systems

DISSEMINATION TECHNIQUES

VLF RADIO

COMMUNICATION/SFB

GBR, NBA, WWVL IxlQ-" ENVELOPE 500 us ^^ASE

~50us

GLOBAL

NAVIGATION SYSTEM OMEGA OxlO"" < 10*/s ~100us

GLOBAL

LF RADIO

STANDARD FREO. BROADCAST (WWVB) IXIO" 'HASE 24h)

ENVELOPE ~50/isUSA (WWVB)

LIMITED

NAVIGATION SYSTEM

LORAN-C

' 2x10-'' *

~l/is(GND) 50us(SKY) 50ms ^^-^ ^.^PHASE

lOus

SPECIAL AREAS

HF/MF

RADIO

STANDARD FREQ. BROADCASTS (WWV) lOOOus

1 DAY^.^^

0 5 mm

HEMISPHERE

NAVIGATION SYSTEM

LORAN-A

5X10-" 2 5us

NOT UTC

A PROBLEM

LIMITED AREAS

TELEVISION (VHF/SHF

RADIO)

PASSIVE -LINE-tO

-11

(24h| ~ 1 us

1 DAY ^^^~33ms

NETWORK

COVERAGE

ACTIVE-LINE-1 (NBS TV TIME SYSTEM) wo""

(<30 mm) <lGOns

1 DAY ^^-^SSms

NETWORK

COVERAGE

SATELLITES (VHF/UHF/SHF

RADIO)

STATIONARY SATELLITES (TRANSPONDER)

ONE y^M

-10 1x10 (24h) 10 us DEPENDS ON FORMAT HEMISPHERE

STATIONARY SATELLITES (TRANSPONDER) TWO WAY

1X10-" (24h) ~100ns DEPENDS ON FORMAT

HEMISPHERE

ON-BOARD CLOCK (ACTIVE) ONE WAY - LOW ALTITUDE

-1x10-'° (24h) 0.5-50US DEPENDS ON FORMAT WORLD

SHF RADIO

MICROWAVE

-13 -1x10

PER WEEK) <lG0ns PHASE COMPARISON LOCAL LINKS

VLBI -H

5x10 ~ Ins DEPENDS ON FORMAT HEMISPHERE

PORTABLE

CLOCKS

PHYSICAL TRANSFER

-,13

1x10**

100ns 1 DAY

LIMITED BY TRANSPORTATION

AIRCRAFT FLYOVER 2-WAY

IXIO'^ < 100ns DEPENDS ON FORMAT

LIMITED BY •TRANSPORTATION

one-month average

ten-day average

12
2.4 Dissemination and Enforcement Network

2.4.1 Central Standards Authorities

Many nations maintain standards laboratories similar to that of NBS. These labs were

formed partially in the recognition that the

maintenance of physical standards is socially

important. They tend to encourage social

order by promoting the economy, protecting

the consumer, and protecting public health

and safety. Because nations are not generally isolated, it is important that many

standards be international in scope. Several international organizations are involved in defining physical standards and

in describing the ways in which these standards should be disseminated. Reference 10 gives considerable detail about the international organizations dealing with date

(time) and frequency (time interval). I will

list just a few of the organizations mentioned

in that reference, with the intent of giving

the general flavor of international activity.

The Bureau International de I'Heure (BIH)

is charged with providing a central international reference point for time and re- lated matters. Based on contributions from

the time scales of about 13 national laboratories (comprising some 60 atomic standards) the BIH constructs the International

Atomic Time scale (TAI) and Coordinated

Universal Time (UTC). Time keeping is complicated by the fact that UTC is based both upon

the motion of the earth and upon atomic

standards. Thus, time-latitude, polar coordinates, stable frequency, and accurate frequency are all inputs to UTC. The International Radio Consultative

Committee (CCIR) makes recommendations with

regard to the formats for broadcasting standard frequency and time. Among its recommendations are those specifying the tolerances

between national time scales and TAI and UTC. With regard to frequency, the General

Conference of Weights and Measures (CGPM) in consultation with its subsidiary organization,

the Consultative Committee for the Definition

of the Second (CCDS) agreed to define the

unit of time-interval (frequency) in terms of

a certain transition of the cesium atom (see

sec. 2.1). Frequency standards are intimately associated with the concept of the frequency spectrum. The allocation (assignment)

of carrier frequencies within the frequency

spectrum is only meaningful to the extent to which those frequencies can be measured and

controlled. The recommendations of the CCIR

with regard to standard frequency broadcasts

are an important factor in providing international compatibility in frequency measurement and control. This is true despite the

fact that the CCIR has no legal authority.

It is advisory to the International Telecommunications Union.

In the United States, the NBS has the

responsibility for developing and operating

the national standard of time-interval. It

is also given the responsibility of providing

the "means and methods for making measurements consistent with those standards."

These requirements are documented in Title 15 of the U. S. Code §272, Sec. 2 and in Department of Commerce Order, DO 30-2A. In compliance with these directives the NBS maintains, develops, and operates a primary

frequency standard based on the cesium atom.

It also broadcasts standard frequencies

based on this primary standard.

In the United States, the United States

Naval Observatory (USNO) is charged with

developing and maintaining the standard

of time and other astronomical data which

are essential for safe navigation at sea,

in the air, and in space. Legal ly , this

responsibility applies only to the activities

of the Department of Defense. The legal

responsibility for these functions is given

to the USNO by the document known as OPNAVINST 5450. 90B Dec. 16, 1969, Mission

and Functions of the U. S. Naval Observatory.

As a consequence of this directive the USNO

maintains an atomic time scale based on a large number of commercial cesium beam frequency standards. And, just as the NBS does,

it must disseminate its standard. It does

this by controlling the broadcasts of several

Navy communications stations. The Department

of Defense (DOD) has given the USNO the re- sponsibility of managing the T&F needs of

the DOD. Both NBS and the USNO are major contributors to the TAI and UTC time scales. The

NBS contributes accurate frequency and

stable frequency and the USNO contributes

astronomical information and stable frequency.

The responsibility for enforcing the daylight savings time changes and maintaining

the standard time zones in this country is held by the Deparment of Transportation,

via Public Law 89-387 and Title 15 of the

U. S. Code. For further details about international

and national T&F organizations and activities

see reference 10.

2.4.2 State and Local Offices of Weights

and Measures

The State and Local Offices of Weights and Measures appear to deal with matters of timeinterval and date by reference to NBS Handbook 44. This document deals with such

devices as parking meters, parking-garage

clocks and "time in-time out" clocks. The

greatest accuracies involved are about -2

13
minutes on date and about 0.1% (1 x 10"^) on time-interval. During a conversation with

an official of the Weights and Measures

Section of the Colorado State Department of

Agriculture, I was told that his office had

the legal authority to enforce the specifications in the NBS Handbook. The penalty for

violating this code is a fine ranging from

$20 to $200 and/or a jail sentence of up to three months for a first offense. It was

his impression that most, if not all, states followed the NBS Handbook 44 specifications

and applied about the same penalties.

Recently the Time and Frequency Division

of NBS has been helping the Colorado State

Standards Laboratory in the calibration of

radar speed guns. The calibration system

we recommended to them involves the use of a commercial frequency counter and a reference

to the WWV broadcast via telephone. The

system more than meets their need for frequency accuracy (which is about 1 x 10"^)

and also gives them NBS traceabil ity, the

latter being a very important legal consideration. Court cases are more solid when

traceabil ity to NBS can be demonstrated.

2.4. i Standards and Testing Laboratories

and Services

In the United States, in addition to NBS and USNO, there are a number of commercial,

governmental, and educational institutions

that maintain standards laboratories, the

majority of which (157) belong to an organization known as the National Conference of

Standards Laboratories (NCSL). By means

of a questionnaire we examined the T&F activity of the NCSL membership. Some 65%

of these laboratories perform frequency and/ or time calibrations and as we had intuitively

expected, they represent an important mechanism for disseminating T&F in this country.

Additional results of this study of the NCSL are given in section 2.5.2.1 and in ref. 11.

2.4.4 Regulatory Agencies

To my knowledge there are only three distinct organizations that have legal authority

in regulating T&F. The Department of

Transportation has authority with respect to time zones and daylight savings time (see

sec. 2.4.1). The state standards laboratories (sec. 2.4.2) have authority within their

own states for time- interval and date measuring equipment. Both of these organizations

deal almost entirely with matters of time.

The third organization is the Federal

Communications Commission (FCC). Unlike the

other two organizations, the FCC appears to deal almost exclusively with matters of frequency. The Code of Federal Regulations,

Part 73, Radio Broadcast Services (Revised

Oct. 1, 1973) describes the frequency allocations and the frequency tolerances to which

various broadcasters must conform. The Code

discusses five categories of broadcasts: AM

stations, commercial FM stations, non- commercial FM stations, TV stations, and

international broadcasts.

There are four major features to the spec- ification:

1. ) The upper and lower frequency bounds of

each of the five categories are given.

2. ) The frequency tolerance for each

category is given as an absolute frequency deviation. For example, for AM stations, the deviation shall be

no more than ± 20 Hz from the specified frequency.

3. ) All broadcasters must check, at least

as frequently as once per month, to see that they meet the specification.

4. ) The NBS broadcast stations WWV, WWVH or WWVB are the ultimate reference to which the broadcaster must conform.

The allowed frequency deviation can be

expressed as a fraction of the maximum operating frequency within the band. The least

stringent tolerance is about 1 x 10"^ (international broadcasts) and the most stringent

is about 1 X 10'^ (TV broadcasts).

It must be noted that the FCC can and does

enforce these regulations. One of the pen- alties they can exact is removal of the

broadcaster's license. It is my understanding

that the broadcaster's license is sufficiently valuable to him that he won't risk being

caught with his frequency down - or up, for

that matter.

2.5 Direct Measurement Transactions

Matrix

To understand the National Measurement

System for Time and Frequency, there are a number of questions which need to be answered.

Among these are:

- What organizations and other groups use Time and Frequency?

- How do they get it?

- Why do they use it?

The Time and Frequency "Flow Matrix" discussed in detail in section 2.5.1 attempts

to give a very concise answer to these

questions

.

Section 2.5.1.1 describes how the matrix

was constructed and defines its various

categories and descriptors. Section 2.5.1.2

14
explains some of the values of its specific

entries and draws some general conclusions.

The Flow Matrix is an approximation to the

National Measurement System for Time and

Frequency as it exists today. There are

pressures now present which tend to alter

some important details of this system. Section 2.5.1.2 also discusses some of these

pressures for change. Finally, section

2.5.2 gives examples of the use of T&F by

several major users. Sooner or later the exceedingly difficult

question arises as to what is the value of a given time or frequency input to a user. Usually, a quantitative answer cannot be

given, nor is it even possible to give a single answer since the questioner usually

wants to know the value of the input in the

future as well as now. Very often T&F is a part of a means to a useful end. For example,

stable frequency is an essential input to the

telephone system whose useful output is widespread communication. On the other hand, the

end-user may have a direct requirement for

time or frequency, such as when the public

uses time-of-day. Despite the difficulties,

some attention should be directed to whether

the benefit of a given T&F input is worth its cost. I defer consideration of this matter

until section 3.

2.5.1 Analysis of Suppliers and Users

2.5.1.1 Construction of the Flow Matrix

The rows of the matrix are labeled by the

various SUPPLIERS of T&F. The columns are given the same labels and represent the

USERS. As the discussion progresses it will

be seen that certain of these categories form

the major suppliers and others the major

users. There is some overlap, and this

approach is an attempt to insure that no important transaction is left out. Listed below are the sixteen SUPPLIERUSER categories. Note that the categories

are sometimes further defined and restricted

by the parenthetical note which accompanies

them. It is necessary to keep this information in mind when considering the value

assigned to the various elements of the

matrix. For the definitions of some of the

acronyms used here, see section 2.4.

1. Knowledge community (science, pro- fessional societies and journals)

2. International metrological organizations (national standards laboratories

BIH, and International Bureau of

Weights and Measures)

3. Documentary standardization organizations (CGPM)

4. Oscillator, receiver, and clock manufacturers

5. Watch industry

6. NBS (T&F and other divisions)

7. USNO (T&F and other divisions)

8. State and local offices of weights and measures

9. Private, and Department of Defense

Standards Laboratories and the Defense

Communication Agency

10. Regulatory agencies (FCC, ITU and CCIR)

11. Department of Defense (operational

mi 1 itary)

12. Other Federal Government (Federal

Aviation Administration, National

Oceanic and Atmospheric Administration,

NASA)

13. Navigation dependent industries

(shipping, aviation, aerospace)

14. Communications industry (telephone,

specialized carrier, TV, radio)

15. Electric power industry

16. General public ("Hams", time-of-day,

private boats and planes)

The question arises as to why these cate- gories were chosen and not others, or perhaps

why not others in addition. The question

really has two answers. First, the general

labels tend to be rather all-inclusive. In examining the characteristics of the National

Measurement System as a whole (T&F as well as

all other physical quantities) there were 14 general categories that emerged. The above

list is the expression of these general cate- gories (with two of them broken into two parts) for the study of T&F. Second, the

parenthetical elaborations represent detailed knowledge that NBS has gained of the

National Measurement System for Time and

Frequency.

In July 1969, the staff of the FrequencyTime Dissemination Research Section of NBS wrote a National Measurement System-type

report entitled "Study of Time and Frequency

Dissemination", to discover if new methods were needed. It identified at least 35 groups and organizations as present and fu- ture users of time and frequency information

and equipment. This comprehensive study

in effect completed the first phase of the

National Measurement System Study: the

identification of all major users of time

and frequency technology.

However, since it was not feasible to study in detail all of these areas within

the allocated time frame, a plan was formed

to narrow the field of study and at the same

time retain the most important users and

potential users. Considerations in the se- lection of the areas to be studied included

judgments of: ; 15
The potential of an organization for helping to deal with problems of significant

social interest, e.g. pollution and

energy, and

The relative dependence of an organization

upon advances in time and frequency technology.

Taking all this into account, I formed a list of eight areas to be studied, which

included a broad cross-section of the time

and frequency community. The areas studied

in detail are shown here:

- Standards laboratories

- Users of NBS radio broadcasts

- Telephone industry and specialized

carriers

- Military

- Position location

- Aviation industry

- Electric power industry

- Shipping and boating industries

These areas are broad enough that it was possible to extract from them most of the

information needed in the 16 categories of

the Flow Matrix.

Consider now the numbers that go in each

of the elements of the Matrix. For many of

the SUPPLIER-USER transactions (i.e. the

elements of the matrix) there are two descriptors:

1. ) The "volume-of-use" descriptor appearing in the center of an element, and

2. ) The "importance" descriptor appearing

in the upper left hand corner of an element.

The "volume-of-use" descriptor has four

possible levels. They are defined as:

0 = Negligible

2 = Occasionally use it but not a common

part of operations

3 = Use often enough that it forms a basic

part of operations

4 = A central part of operations. Used

continuously or very regularly.

In these definitions I have avoided an ex- plicit statement as to the relationship

between the T&F input (from supplier) and the

social value of an organization's (user ' s)

output . The "importance" descriptor also has four

possible levels, defined as:

1 = Purely a matter of convenience

2 = Economically compelling or strongly

desirable

3 = Legally required or alternate sources

unsatisfactory.

4 = Matters of life and death or sole

source.

These definitions contain some very strong

socio-economic judgments. They should be

interpreted as referring to the value of

the T&F input in the user's internal operations and not to T&F's value to the output

of the user.

It is necessary to be specific when assigning values to either of the two descriptors

as to the nature of the time and/or frequency

output from a supplier. It is desirable to distinguish eight specific categories. They

are:

A. A T and/or F source (a piece of equipment)

B. A disseminated T and/or F signal (an

electromagnetic wave)

C. A receiver for T&F signals

D. A particular dissemination means

(equipment) for T&F

E. Published information about T&F

F. Consultation about T&F

G. Regulations and/or specifications

for T&F

H. Requests for T&F equipment or services

A letter appears in the lower right hand corner of each element. It identifies the

output upon which the values of the two descriptors are based. In a few instances - because I have more information - I have

sometimes identified more than one output.

Note, in this case, that it is always the

first letter upon which the descriptors are

based.

It should be particularly noted here that

in one case the "supplier" supplies requests

for T&F equipment or services only, and not T&F equipment and services themselves.

Only direct transactions were allowed in considering the values to be assigned to the

various transactions. For example, if a quartz watch manufacturer provides watches

to the general public, that is a non-zero transaction of the 5, 16 type, i.e. of the

Watch Industry-General Public type. If a quartz oscillator manufacturer provided the

watch manufacturer with the quartz oscillators that went into the watches, this

would not be an allowable interaction of the

type 4, 16. Therefore, if no direct interaction exists then the "volume-of-use"

descriptor is zero. And, obviously, so is the "importance" descriptor. It should be

carefully noted again that any given ranking

was based only on one output from the supplier.

In many -cases a given supplier provides more

than one input to a given user; I have

16
1^

<•

General i£ Public 0 0 0 ro ro 0

CD 0 :m CO

CM 0 0

cc CM

CC ro

Electric ^

Power Ind.

D

CM 0

CJ

CM

<M

<t cc rocc CM 0

< CM

C3

CM

CQ CM

0- 0 0

CC CO

ro X ro CM

Comm. ^

Industry

u n

a u

00

CQ

ro

•a CM

u

ro CMCM 0 ro

CD

ro ro ro

CM 0

OC CM

3:

--J- ro

CQ

ro CM X

ro

CM NavigationDependent "

Indus fry 0 a 1 0 0

ro a

ro

cr CC 0

< ro

CD

ro 0

cc CM

CM

CQ

ro 0

Other ~

EficL^Qi'J-..

ijj ro a

^J 0

0

CM ^ •=1 CM Xro CJU

CC ro 0 ro

CD

ro Q CM 0 0 ... CO

Dept. of := Defense 0 0- 0

<_)

CO

ro < ro

CO ro

cc 0 ro

CD

ro

QQ CM

rj- cn

cr CM

CM

co 0

Regulatory °

Aqencies

0

u

CM

II on 0 0

QG ro

ro

cc ro CM 0Lu CO 0 CMU. ro

CM CD 0

DOD & Private <^ Std. Labs.

U- u

CM 0 < ro

ro 0 cc ro

ro

ro 0

< ro 0 ro ro

n: CMcn ro

CM

CO CM 0

:l S&L CM 00 OWM ' s

Ll CM 0 0 CM

u.

CM ro

ij_ cn

CO

0

Lu

ro 0 CM 0 0 0 ro

°^ cn

CO

-./I 2: o CO

<x on CO u

(O <c

ro 00 CM

CO CM

3: CM Q ro CM~'~ X

CM ro 0

ZL CM

^ CQ LTt CO ro

~^ ro

ro 0 ^

0 ro

ro

CM cm'"ro

CG

ro CMro

r\j CM

ro

x; CM

CM

ro

CM CMOJ CM

CM

zt: CM

CM

Watch

Industry

0

u

CM 0 ro

cn

CO

ro

00 CM 0

00

0 0 CM 0

IC CM rO

CM 0

3. CM

Osci 1 lator & Receiver Man.

LU CM PO 0u_ 0

Ucn no

CM

CO

?o CM

ro CvJ re CM X

CM CM

ro

:m CM (SI

Document "

Stand. Orgs.

UJ

CM u

ro u 0 0

u_

ro

ro

u,

ro ro 0

m ro 0

U.

CM 0

Ll. CM 0 0

Int'l . Metrol . ~

Orqs

UJ ro

Ll ro

=3: ro

'JZ CM

LL. CQ

ro

CQ

PO 0 CM

zc: CM X CM X

CM X CM

Knowledge

Community

UJ

CM CM 0 0 0

jj CMUJ

CM 0

UJ

CM

LU

CM 0 CM

CM 0 0

DIRECT

MEASUREMENTS TRANSACTIONS

U

MATRIX

FOR

S E R S

en

LU

_J

D.=3

<u >>

CD !->

dJ c

r- rj 2 E 0 e c 0 NX 0

0

s- +J

OJ s:

c ^

CM

-M 0 c

OJ • E -0

z) c: 00 CO

ro

s- s: 0W s-

<— >

•<- OJ u 0 0

i-

(-> U 3

+-> "D

U- CO 1—

to

0 Ll_ ^ 0

00

<\i +-> >

i~ -O

Q_ ra _J 0 +^

>>

s_0 l/l 4_> <U

fO -f- r— U

3 C

C7> QJ

0

0 OJ

(/)

• C

+-> OJ cmOJ tu

0

CD

S_a> • J= X3

CM

C

c

0 -M

r- C

+-> r.) fO "O

cn c

•.- O) > CL

ro

c

0

l-> (O0

C +J 3 t/1 E 3 e -o 3

^

S-

<u0 >,

o_ C-

• t/l U 3

CU TD f— C

i. —

cS (5

17
stressed the most important input in each

case. The hope is that this will define the

primary characteristics of the system.

For the majority of the elements only one number appears, it being my estimate of the

"vol ume-of-use" descriptor. I did not attempt to estimate the "importance descriptor", feeling that my knowledge was insufficient for more than one estimate.

A word of warning: the reader should not attempt to interpret the T&F Flow Matrix in terms of the social value of T&F to the end

user. The intent of the Flow Matrix is simply to define some characteristics of T&F flow from supplier to user.

2.5.1.2 Nature of the Suppliers and Users

There are three elements comprising this

section: first, some examples of how values were assigned to the descriptors; second, some general conclusions about who are the

major suppliers and users; third, changes

which have occurred or will probably occur

in the supply and use of T&F. The purpose of the first is to give the

reader a feeling for the considerations in- volved and not to list the values assigned

to all the elements. In the second subsection, I generalize about the function/s

that time and/or frequency perform for the

major users. Third, I discuss whys and

hows of actual and possible changes.

The question of change quickly gets into

socio-economic considerations. Nevertheless,

I still attempt to confine this to its meaning to the users' internal operations, the

problem of cost-benefit analysis and the

end user being reserved for section 3.

2.5.1.2.1 Examples of Assigning Values to the Descriptors

Examples of seven of the eight types of T&F output listed in section 2.5.1.1 are given here. An example of a frequency source occurs

in transaction 4, 11 (Oscillator Manufacturers-Department of Defense). The military

uses its atomic oscillators often enough

that level 3 in the "vol ume-of-use" descriptor applies. Calibration with a standard

frequency signal is often not possible, or

at least not desirable, so they need the

frequency accuracy of atomic oscillators

which they cannot produce themselves. Thus,

the "importance" descriptor is rated 3. An example of a time signal is in trans- action 6, 13. The yachting community uses celestial navigation and therefore date, for

position location on the open sea. When it

is needed, it is used at least once per day.

so level 4 of "volume" applies. When celestial navigation is being used it could be a matter of life and death to obtain an adequate "fix". It also is sometimes true that

the NBS (WWVH) signal is the only one available. Thus, I have assigned a value of 4 to "importance". If electronic position location equipment (Loran-C, Omega) is also on board and working, then this "importance"

ranking would not be correct. Since electronic position location is at least a potential alternative, some readers may still

object to a ranking of 4 for "importance".

I stress again that the Flow Matrix is to be

interpreted as a "snap shot" of the present.

Another example of signal as an output is

7, 6. The NBS compares its time scale with

that of the USNO on a very regular basis,

thus level 4 of "volume" applies. "Importance"

is given a value of 3 because the liigh quality

of the USNO time scale means that not to do

so would be exceedingly unwise.

A great many jewelers listen to the WWV time-of-day broadcast in order to calibrate

their watches and clocks. To do this, they

must have a Teoeiver. For the 4, 5 trans- action, "volume" is 3. Because the jewelers

cannot, in general, build their own receivers,

"importance" is also 3. The American Telephone and Telegraph Co. owns and operates a very extensive, highquality, 1 ine-of-sight microwave dissemination system. The major TV networks maintain

rubidium frequency standards in their studios,

which are used to frequency stabilize the

broadcasts. The stability (roughly speaking)

of these standards is disseminated over the

microwave system and the signals are regularly monitored by NBS. Some of the standards

laboratories of the U. S. Navy are, or very

soon will be, using this system to calibrate

the frequencies of their own oscillators.

Since this will be a basic part of their T&F operations, the 14, 9 transaction is rated

3 for "volume". Because of the high quality,

relatively low cost, and traceability to NBS

of this service, we consider its use strongly

desirable. The "importance" is judged to be

2. Many people use NBS T&F publications but

often it is not a basic part of their operations, e.g. the science community often

uses it as background knowledge. Thus the

"volume" ranking of 6, 1 is 2. From the

point of view of the National Measurement

System for Time and Frequency, it is strongly

desirable that this information be available,

so I have assigned a value of 2 to "importance". Consultation is a very important part of

the activities of many T&F suppliers. I have chosen, however, not to assign any of

18
the rankings in this matrix on the basis of

this output.

Regulations set forth by the FCC for the

frequency accuracy of broadcasting have

legal force and require regular attention by

the broadcasters. Therefore, both the

"volume" and "importance" descriptors of 10, 14 are rated 3. By keeping its average frequency very near

60 Hz the electric power industry of this

country is a profoundly important part of

general-use time keeping. The public has come to expect this service and sometimes,

in fact, the publ ic"request" it. Accordingly,

the "volume" measure of the 16, 15 transaction

is 3, and the importance level is 2.

2.5.1.2.2 Major End Users and Their Suppliers

The National Measurement System for Time

and Frequency is a complicated system.

The Flow Matrix was designed to make the flow

of T&F outputs comprehensible, but even with

this it is difficult to grasp the essence of

the T&F flows. One important thing we can do

towards understanding the Matrix is to identify the major end users and categories which

supply them. An end user category (1, and

10-16) is one which uses T&F as a means to an end and not as an end in itself. Thus, the

telephone industry (part of category 14) is an end user because it uses accurate frequency

to control its frequency division multiplexing

system. The NBS is not an end user because

it uses virtually all its inputs to improve

or check its ability to generate and disseminate T&F.

It is meaningful to define a major end user as one for whom both descriptors are

rated 3 or higher, thus 10-16 are major end

users. The suppliers of these major end users are categories 2, 4-7, 9, 10, 11, 14, and 15. The general public (category 16) may be

classified as both a major end user and

supplier in that it reads its own watches and

clocks. This is a skill usually taken for

granted but it would greatly alter society

should this ability be limited to a few

peopl e. It might be questioned whether the regulatory function as performed for example by the

FCC, can legitimately be considered a T&F input. Since it clearly restricts the system

and in some ways gives it stability, I contend that it is useful to do so. In user categories 10 through 16, there

are three recurring functions which T&F per- forms for the user: communication, navigation, and coordination. The ability to divide frequency and time/space provides the

communications function and is of major

importance in categories 11, 13, and 14.

The relationship between time and distance

provides the navigation (position location)

function which is vital in categories 12 and

13. The aspects of constant rate and the

ability to facilitate simultaneity provide

the coordination function which is basic to categories 11, 12, 15, and 16. Defining the needs for accuracy and/or

precision could be accomplished by adding

another descriptor to the Matrix, but in my

opinion, the value added would not be worth

the additional clutter. This is a topic which

arises in discussing change and appears in the next section.

2.5.1.2.3 Directions of Change in the

National Measurement System for

Time and Frequency

This section examines three major technical areas where changes are occurring or will

probably occur. These areas are as follows:

1. By 1980-1985 there will probably be a widespread network of clocks which are synchronized with respect to each

other to between 1 and 10 microseconds.

2. Within that period there will probably

be a widespread network of terminals

that are equalized in frequency with

respect to each other to about

1 X 10"^^ Very likely, all of the

clock locations of item 1 will be

among these frequency equalized terminals. There probably will be many

others in addition although the needs

for frequency equalization beyond the

1 X

10"-^° level will usually have a strong relation to timing activity.

3. There may be significant pressure from

the public for a 100- fold improvement

in the accuracy of time-of-day, widely

available, for setting watches and

clocks

.

As in most situations of possible change,

there will be pressures (socio-economic as well as technical) for preservation of the status quo as well as for alteration. My comments contain inherent socio-economic con- siderations but I will confine my detailed

discussions to technical matters. A brief

economic rationalization behind these pre- dictions may be found in section 3.

2.5.1.2.3.1 Time Synchronization and Position

Location

There exist today, in addition to portable

atomic clocks, three (widespread) means for

synchronizing clocks to 10 ys or better. In order of accuracy, they are: 1.) Omega

19
(about 10 ys), 2.) Loran C (about 1 us),

and 3.) the Defense Satellite Communication

System (about 0.3 us). Omega and Loran C are both networks of transmitters used for

navigation purposes. The Defense Satellite

Communication System is a network of satellites used for the purpose of communication.

All three of these systems are expensive

(a minimum of $5000 per receiving site

for the least expensive system) and difficult to use. The NBS broadcast stations

WWV and WWVH provide a widespread means of

timing that is simple to use and of low cost (about $200/site). However, this

service is only capable of about 100 microsecond synchronization.

There is presently a debate as to whether

there is a requirement in data transmission

for a communication network that has nodes

that are synchronized to a tolerance in the

range of 1 to 10 ys. The opponents of such

a system say, for example, that it would not

be economically useful because it is more

efficient to time the nodes on a pair-bypair basis by sending synchronizing pulses

along with the data. They claim that since

storage buffers are needed in the timed net- work as well as in the pair- by- pair system

to adjust for different fixed delays, it is wasteful to continuously maintain a synchronized network. The advocates admit that buffers would still be needed but argue that for

a many-node switched system, the timed net- work offers an important increase in flexibility.

This argument becomes quite involved; how- ever, I believe it will be settled in favor

of the proponents and within five to ten years, a widespread time synchronization

capability will be available. This will

exist in the form of one or more systems that

can synchronize a network of clocks to a tolerance of from 1 to 10 ys. One such

possibility is a set of nodes interlinked by

1 ine-of-sight (LOS) microwave lines such as

is now being tested by Bell -Canada. In this case, the synchronizing system and the clocks

to be synchronized tend to become indistinguishable.

Two general comments about the feasibility

and utility of such a system are appropriate.

First, LOS microwave transmission has a proven path stability of the order of tens

to hundreds of nanoseconds over the period

of a day. This applies to paths of from 20

to 2000 miles. (If, of course, there is more than one path between two points and a switch is made between paths, then the delay

change will be vastly greater.) This means

that for LOS microwave, path instability is not limiting at the 1 ys level. Second, a widely available time scale does have the

capability of coordinating systems which are time-dependent but which were initially independent. Thus, if a timed network develops

within the telephone system, there may be

socio-economic advantages to making this time

available to other time-dependent systems.

Partial support for my opinion that the

1-10 ys timed network would be useful comes from a recent polling of T&F experts. In this poll there was a rather strong opinion

that such a system, if available, would be

in extensive use between 1980 and 1985. This

poll is discussed in section 3. One of the things that would aid the

technical-economic feasibility of such a system is good, low cost, frequency equalization,

reviewed in section 2.5.1.2.3.2.

Even more sophisticated synchronization

systems are being proposed for purposes of

position location. The most ambitious of

these is the Global Positioning System under

development by the U. S. military, based on

a global network of satellites, each carrying an exceedingly stable clock. The goal

of this system is to be able to locate pos- ition anywhere in the world to a repeatability of about ten feet. This corresponds to being able to predict satellite-to-ground

path delay at least as well as 10 nanoseconds

for any given path, at any given time, on any given day. The NBS knowledge on this

matter suggests that the present state-ofthe-art in predicting satellite-to-earth

path delay is no better than 10 nanoseconds.

The designers of the system hope to achieve

this performance without synchronizing the

satellite clocks more often than once in

2 weeks. This translates into a frequency

stability requirement of about 1 x 10 for

a 2-week averaging time.

2.5.1.2.3.2 Frequency Equalization

It is helpful to briefly review the major

needs for frequency equalization in the

order of increasing needs for accuracy and/

or precision. The approximation used here

is that the needed calibration system is about

ten times more accurate or precise than the

inherent capability of the device to be

cal i bra ted. The typical mechanical wrist watch is capable of maintaining time-of-day accuracy

to about one minute over one day's time. An error in average rate (frequency) of about

1 x 10"^ would produce this much time error over one day's time. Thus, a source of frequency calibration should be accurate to about 1 X lO""*. The newer generators in the electric

power industry are capable of having their

frequencies reset to about 1 x 10 ^ Hz, or

20
roughly 1 x

10""* of the nominal 60 Hz. It

is therefore desirable to have a frequency

reference at_60 Hz which is accurate to about 1 X 10 ^

The FCC applies a legally-backed requirement on the frequencies of all broadcasts.

As discussed in section 2.4.4 the most

stringent requirement, about 1 x 10'^,

applies to the TV broadcasters. Because the

law requires that the calibration be trace- able to NBS, the calibration source should

be accurate to about 1 x 10 ^. There is now

a significant possibility that the FCC will

require the operators of cable TV systems to maintain their carriers accurate to 1 x 10"^.

This would make a source accurate to

1 X 10"^ very desirable. If such a rule is imposed it would probably come to apply to

all TV broadcasts.

Note that frequency control or measure- ment requirements beyond about 1 x 10 ^ -

1 X 10~^ press the limit of widely available,

lowest cost mechanism: WWV-WWVH. There is a specialized but very widespread application for frequency equalization

within the telephone system: frequency

division multiplexing (FDM) requires that

frequency be equalized at about 50 places

in the U. S. to approximately 1 x lO"-'". The Bell System appears to be satisfying

their own need in this regard (for more detail see sec. 2.5.2.3). There is an international organization which debates matters

of this nature, the CCITT (Consultative

Committee on International Telephone and

Telegraph). In a recent meeting, the

Committee agreed to recommend a frequency

tolerance of 1 x 10"^^ for international

coordination of the FDM networks of the

various telephone systems. The actual technical need for now and the forseeable future

is more like 1 x 10"^°. [12]

The state-of-the-art frequency drift of

quartz oscillators is about 1 x 10 ^Vday.

Thus, for the telephone application and even

for the probable new FCC requirement on TV,

it is necessary to use atomic oscillators in the operation of the system or at least to have easy access to them.

This brings me to another very important

point. There are some applications for frequency equalization in the range of 10 ® to 10"^° wherein it is undesirable to be

"hooked in" to a frequency equalizing net- work. The portable clocks of the Global

Positioning System are one example; part of

the FDM network of the telephone system is another. Oscillators meeting this requirement now cost about $5000 or more. There

would probably be a significant market for

a device in the range of $1000 to $2000 (see

21

sec. 3.2).

Beyond about 1 x 10"^ ° there does not seem

to be large technical need for frequency

equalization per se. Past this level, frequency equalization requirements become a part of the requirements for time synchronization. For example, if it is desired to maintain clocks in synchronism to 1 ys and not resynchronize more often than once per day, then the frequenoies of the clocks must

be equal to one another to somewhat better

than 1 X 10"".

Just as for time synchronization, it is useful to look a little further into the

future. A single link of an LOS microwave

system does have a day-to-day path stability

of about 10 nanoseconds. If a person wanted

to take full advantage of this for the pur- pose of time synchronization, he would want oscillators which were stable, _averaged over

one day, to better than 1 x 10 and would

need them equalized to about this level. This

is pressing the state-of-the-art of commer- cially available atomic frequency standards.

For information on the state-of-the-art of

commercial and laboratory frequency standards

the reader should consult reference 13.

2.5.1.2.3.3 Improved Setting of Watches and

Clocks

The time of day, provided by watches and

clocks, may be obtained nearly anywhere, anytime. The electric power industry (EPI) pro- vides fairly accurate average frequency

(averaged over one day) , and as electric

clocks are phase accumulators (adding up successive time-intervals), time correct to the nearest minute is fairly easy to come by.

Conversely, it is very difficult to set the position of the second hand with respect

to the minute and hour hands. Thus, the

aocupaoy with which time-of-day can be obtained from the typical watch or clock is roughly 30 seconds. The basic use of the

second hand has been to make relatively

accurate (about 1 second) measurement of fairly short time intervals (a few tens of minutes

at most)

It now appears that we are within five

years of a significant change in the watch

and electric clock situation. With the availability of watches and clocks with digital

displays it will be easy to set the seconds

reading with respect to the minutes and hours

reading. Therefore, for the first time on a widespread basis the seconds display can have

good accuracy, not only because a change of one second is clearly resolvable, but because

the rates (frequencies) of the watches are accurate enough that their probable daily

error is approximately one second versus one
minute, as with the usual watch.

The point is not that many people need

time-of-day accurate to one second, but

rather that, for the first time, a great

many will become aware of the fact that there are variations of as much as 30 seconds be- tween sources which they had heretofore

considered accurate.

Will many people care about this improved

accuracy? If they do, the present availability of proper calibration is inadequate and we can expect to see a significant up- grading of the time-of-day service offered

by the telephone industry. It may also

place an additional burden upon the telephone

time-of-day service of NBS. I discuss this

matter again in section 2.5.2.2.

As stated earlier, the electric power

industry is a very important source of time,

attempting to hold its average frequency

close enough to 60 Hz that the accumulated

time error over one day's time is no more

than two seconds. But I have been informed

that in areas where the power system is over- loaded the time can be in error by as much as 30 seconds. It may therefore be that the

relationship of the electric power industry

to time-of-day is about to change.

2.5.2 Highlights of Major Users

2.5.2.1 Standards Laboratories

The study of the standards laboratories

was conducted by sending a questionnaire to each of the members of the National Conference of Standards Laboratories (NCSL) [11]. As of February 1, 1973, NCSL listed 257

standards labs in this country, and of these,

157 are NCSL members. Some 68% of the NCSL membership responded to the questionnaire.

Of the responders, 96% perform regular

frequency calibrations and 80% do timeinterval calibrations. Presuming that those

that did not respond do neither frequency

nor time calibrations, about 65% of the NCSL performs regular frequency calibrations.

Assuming that the non-NCSL labs have the same distribution as the NCSL labs, then 65%

is the approximate participation of all standards labs in this country in frequency

calibration. If the extreme assumption is made that none of the non-NCSL labs perform

frequency calibrations, then approximately

40% of all the standards labs in the country

do this work. At any rate, the standards

laboratories of this country appear to be an important means of obtaining frequency and

time-interval calibrations.

Of those NCSL members performing frequency

calibrations, 70% of them required accuracy

better than 1 x 10~®. Of those responding,

about 11% own cesium beam frequency standards,

5% own rubidium standards, and 85% regularly

monitor one or more of the NBS standardfrequency broadcasts. Summing the estimates

of the individual respondees, I estimate

that these 98 labs perform about 50,000 frequency calibrations per year.

2.5.2.2 Time-of-Day to the Public

In 1974, about four billion telephone

calls were made to obtain either time-ofday (TOD), weather information, or both [12]. It's estimated that the number would have

been about two billion if the only service

offered was TOD. The service is available throuqh the telephone system by means of about 1 ,000 TOD

machines, based on a pre-recorded tape,

placed in telephone company central offices.

The recording is synchronized to TOD (UTC)

by receiving the broadcast from the NBS radio

station WWV. There are two types of TOD machines in use, the major difference to the user being

the accuracy with which time is received.

The device giving TOD at the lower level of

accuracy announces time to about the nearest

one minute. This unit begins announcing a given minute 25 seconds before that minute

occurs and continues the same announcement

for one minute. Thus the time can be as far off as about 30 seconds.

The device which provides the higher

accuracy announces the time every ten seconds and says something like, "At the tone

the time will be —." This device_has a precision of better than 0.1 ms (lo'"* sec- onds). The accuracy available to the user

will vary from telephone to telephone and

from day to day. As received at those

offices that deliver the time every ten seconds, the time will be accurate to about

five to 15 ms. This depends on the propagation delay which is primarily determined by

the distance between the WWV transmitter and

the office. It is my understanding that an approximate propagation delay correction is made at some of these offices. If so, the

time disseminated from the TOD machine should

be accurate to about 1 ms. The time as re- ceived by the telephone user will, however,

be much less accurate, because the telephone

network can have large and changeable time

delays. Personnel at NBS have done a few

experiments with this "every ten seconds"

service and find that it is usually accurate,

at Boulder, Colorado, to about 100 ms (0.1

seconds). The average user of this "every

ten seconds" service would usually find the

accuracy at least this good; however, no one is giving the user any guarantees on the

22
accuracy of the system.

A study based on a very restricted sam- pling indicated that one of every 134 users wanted one second accuracy some of the time.

If, however, digital watches become common,

perhaps a greater number of people will re- quest this accuracy (see sec. 2.5.1.2.3.3).

2.5.2.3 Technical Requirements for Frequency

Equalization within the FDM Network

of the Telephone Industry

In the U. S. telephone industry, essentially every phone call that traverses more

than about 50 miles is carried by what is known as the frequency division multiplexing

(FDM) system. It has some rather stringent

frequency equalization requirements. In order to recover the message at the receiving

site, an operation known as "reinserting the

carrier" must be performed. If the call

travels a long distance, such as from coastto-coast, as many as five complete stages of

multiplexing may be needed. Each of these

stages involves the operation of carrier re- insertion. An oscillator used for reinserting a carrier must be closely equal in frequency to the oscillator which was used for

transmission. An inequality between the frequencies of the two oscillators tends to garble the message. The present specification in the telephone industry is that the

offset in frequency between sending and re- ceiving ends be not more than 2 Hz. If the

full five stages of multiplexing are used

then the absolute frequency tolerance on each

oscillator is 0.2 Hz. In this case, the

nominal frequency of the highest-frequency

pair of oscillators in the chain is about

60 MHz. Thus, the fractional tolerance on this pair of oscillators is 3.3 x 10"^. The

nominal operating frequencies of the other

oscillator pairs in the chain is less and the

fractional tolerance is correspondingly less.

[12]

The need for frequency equalization has

grown markedly over the years, because the

number of levels of multiplexing has greatly

increased and the tolerable frequency offset

has grown smaller. Figure 4 shows the increasing need for frequency equalization.

The needed frequency equality is achieved

by sending signals, pilot tones (around the

country on the telephone facilities) to which

the various oscillators can be slaved. For some 40 years, up until about 1973, the sources of these pilot tones were quartz

oscillators, kept stable in long-term by

tracking the broadcasts of NBS. During the

1960's and the early part of the 1970's, the

NBS station WWVB was used as the reference.

^EAR OF INITIATION OF NEED Figure 4. Development of frequency accuracy

in FDM system of telephone industry

With the appearance of the latest (fifth)

level in the FDM hierarchy in 1973, the pilot

tone system based on quartz oscillators has

become inadequate. Because of this, the

American Telephone and Telegraph Company

(AT&T) is putting a new pilot tone system

into operation.

This new frequency equalization system

will be used by the entire telephone industry

(Bell System and independents) as was the

older system. It will be based upon a group

of three commercial cesium beam oscillators,

one of which will be "on line", the other two serving as backup, permitting the detection

of a fault in any of them. Two signals will be sent out from this

facility - 20.48 MHz and 2.048 MHz - to each

of some 30 to 50 sites around the country.

The cesium oscillators will be located at Hillsboro, Missouri. These signals will be

disseminated on the 1 ine-of-sight (LOS) micro- wave system of AT&T and on the three highestquality coaxial facilities in their system.

The 30 to 50 sites to which these pilot

tones will go will be equipped with sophisticated quartz crystal oscillators which are

known in the industry as Jumbo Frequency

Supplies (JFS), devices which have a freerunning drift rate of less than 1 x 10"^°/

day.

The oscillators (carrier supplies) for the

FDM system are located in more than 25,000

telephone offices which are known as Central

Offices, 2, 000 of which are designated as Toll

Offices. These Toll Offices require carrier

supplies for the FDM system

In the hierarchy of the old system, the next level below the pilot tones was known

as the Office Master. These locations are

also known as Primary Frequency Supplies

(PES). The PES is a device based on a quartz

oscillator (actually two quartz oscillators)

which costs about $2500 per unit and which

has a free-running stability of about

23
1 X 10"^/ day. In the oscillator hierarchy,

this second level is the lowest level in terms of quality of oscillators used; there

are no lesser quality oscillators in the FDM system. However, in view of how the various

Toll Offices are interconnected, it is roughly correct to say that there are five

levels in this hierarchy, including the

pilot tone. The PFS's are phase-locked to- gether in groups of about four. (Bell

System policy is to try and avoid cascading more than four PFS's in one chain.) Thus,

the first PFS in the chain is phase-locked

to the pilot tone, the second PFS is phaselocked to the first, and so on. This phaselocking procedure was a basic difficulty

with the old frequency equalization system

because transients in the system (usually

due to routine system testing) tended to break the lock. The further down a chain a given PFS was located the more susceptible

it was to these transients. Apparently, the

disturbance was so bad that at times,

fractional deviations in frequency as large

as 1 X 10~^ occurred.

The second level of the hierarchy of the

new frequency equalization system is the JFS mentioned above, the first level being

the cesium beam oscillators. Unlike the old

system, this second level will not be phaselocked to the pilot tones. The JFS's will

instead be pseudo frequency-locked in such a manner that they are offset from the pilot

tones by 1 x 10"^°. In the old system,

transients occurred in the pilot tones,

whereas the new system should have less

trouble with "phase hits". The pilot tones

of the new system will be more stable in long-term and this should prove helpful.

The rest of the new system, as originally

planned, will be phase-locked as before.

Here, a JFS will be the initial source in the chain of phase-locked oscillators.

Some within the Bell System feel that this new frequency equalization facility will still not adequately solve the "phase hit" problem.

Thus, some consideration is being given to further breaking up the phase-locked chains.

By introducing an oscillator which is sufficiently stable in long-term, say 1 x 10"^°

for periods of a week or longer, a pseudo

frequency-lock could be substituted for one

of the phase-locks.

A final point: it may be that it is now economic to substitute low-cost atomic oscillators in the FDM system for part of the

quartz oscillators in order to further break

up the present phase locking. An atomic

oscillator which could be sold for no more

than $2000 would probably be quite proper

from a cost-benefit viewpoint. How many of

these oscillators might be required?

The present policy of the telephone industry is to try and avoid cascading more

than four oscillators into a single chain.

If, on average, there are four oscillators

per chain, then there would be about 500

chains in the total system. If the lead

site in each chain were atomic, then 500

atomic oscillator sites would be required.

Since each site requires two oscillators,

the total number of atomic oscillators would

be 1,000.

In summary, the new frequency equalization

facility for the FDM network has the following characteristics:

1. ) Frequency, accurate to about 1 x 10"^^

will be available to the telephone

industry at about 50 places widely

dispersed around the U. S.

2. ) At each of these sites, frequency that

is usually accurate to about 1 x 10"'°

will be dispersed to about 15 chains

of phase-locked oscillators.

3. ) The frequency accuracy available from

these oscillators is difficult to predict. It can be said, however, that

it tends to degrade, the lower a par- ticular oscillator happens to be in a chain.

4. ) The lowest fractional accuracy that

can be tolerated in the FDM system is about 2 X 10"^ and at certain levels

of the multiplexing hierarchy it must

be at least as good as 3 x 10"'. (I use the word accuracy rather than pre- cision to emphasize that the pilot

tones are based on a cesium beam os- cillator. ) 5. ) It seems that it would be cost beneficial to introduce about 1,000 atomic

oscillators into the system to further alleviate the "phase hit"

problem. To be economic, these os- cillators could probably cost no more

than $2000 each.

2.5.2.4 Two Electronic Position Location

Systems

2.5.2.4.1 A Loran-C System

In section 2.5.2.5 I discuss celestial

navigation as a means of locating position.

It is pointed out that there are electronic

means of position location that are much more accurate, albeit much more expensive.

24
This section discusses two such systems and

their requirements for time and frequency.

There are several other versions of electronic navigation systems; however, the

two specific examples described here reveal

the principles upon which any such system is based.

The first method uses the Loran-C navigation network operated by the U. S. Coast

Guard. This system consists of about 35 transmitters located in eight geographical

areas: U. S. East Coast, Mediterranean,

Norwegian Sea, North Atlantic, North Pacific,

Central Pacific, Northwest Pacific, and

Southeast Asia. Thus, although the availability of the system is limited to these

general geographical areas, there is sufficient coverage that the system is of

great utility.

For precise position location with sys- tems of this type, the signals received

from the transmitters must, primarily, be

due to the ground wave. For the Loran-C

system, whose transmitters operate at a carrier frequency of TOO kHz. The sky wave

begins to seriously interfere with the

ground wave for distances beyond about

1000 miles from the transmitter. This

system and others of its type, such as Omega, are based on two facts: first, all of the transmitters broadcast with nearly

equal phase, and second, the geographical

location of each transmitter is accurately

known. With Loran-C, as with all electronic navigation systems, the site at which

position is to be determined must have a proper radio receiver and have or have access to, electronic computation equipment.

The specific system under discussion is known as a rho-rho-rho system, meaning that

the absolute distance from the receiving site

to each of three transmitters is measured.

Imagine for the moment that only two trans- mitters are used. Around each of the trans- mitters, circumscribe a circle, the radius

of which is equal to the corresponding measured distance; except for the special case where the two circles are tangent to one an- other, they will intersect at two points.

The position of the receiving site is located

at one of these two intersections. Even a very rough idea of where the receiving site

is with respect to the transmitters will

usually suffice to determine at which of the

two intersections the receiver is located.

The radio equipment at the receiving site is used - in conjunction with the fact that the

transmitters are broadcasting in phase - to determine the needed distances. This application of the Loran-C system is not the

usual one. Normally it is only the difference in time of arrival of the two signals

which is measured. The system under discussion actually uses more information be- cause, knowing the total propagation time of

each signal, the user also could calculate

the difference in time of arrival.

One of the components of the receiving

equipment is a very stable frequency standard

operating as a clock, the purpose of which is to measure the time delay between the time

of broadcast of a particular signal and its

reception at the receiving site. To do this

it must not only be operating at the same frequency as that of the transmitters, it

must also be in phase with them.

With this information we can now examine

the performance and T&F requirements of this

specific rho-rho-rho system. If the clocks

at the receiving site and all the trans- mitters were exactly equal in frequency and

phase, and there were no electrical noise,

then a rho-rho system (only two transmitters)

would provide all the position accuracy re- quired. None of these conditions, however,

is true. The biggest common deficiency is probably that of the clock at the receiving

site. As a partial and important compensation for real-life deficiencies, a third

transmitter is used, providing a measure of

redundancy which makes the limitations less severe.

To provide good clock performance at the

receiving site, a cesium beam frequency

standard is used. (The Loran-C network is also based on cesium standards at each trans- mitter.) Expressed in terms of time, these

transmitters are kept in phase to about

0.1 ys. Just from the point of view of the

transmitters this corresponds to a distance

measuring accuracy of about 100 feet.

Consider now the limitations of the per- formance of this Loran-C system imposed by

the imperfections of the clock at the re- ceiving site. Knowledge of cesium beam performance permits a general comment: commercial cesium beams have an accuracy of about

1 x 10"^^, Assume that this is, in fact,

the frequency difference. If the receiving

clock were set exactly in phase with a trans- mitter at a given time then it would be out of phase by 0.1 ys some two and one-half

hours later. The error due to the receiving

clock would be essentially equal to that due

to the small phase inequality of the transmitters. If the frequencies could be equallized to 1 X 10" ^2 then the elapsed time to accumulate a O.lys error would be one day.

The manufacturer of this system claims

that the diameter of the circle of probable error is about 65 meters (200 ft.). Accuracies of this magnitude are apparently quite

useful but other information at our disposal

indicates that a reduction of the circle of

probable error to about ten meters would be

desirable. The total cost per receiving

25
site for this particular system is currently

about $50,000.

2.5.2.4.2 The TRANSIT Satellite System

The TRANSIT system is a group of three

satellites which orbit the earth about once

every 90 minutes. It belongs to the U. S. Navy and is operated, under contract, by the

Johns Hopkins University. (This is part of

the total military time and navigation system mentioned in other sections of this

report called the Defense Satellite Communication System and is available to civilian

as well as military users.)

The TRANSIT method is based on the

Doppler effect, the well-known experience

that the frequency of a constant frequency

source appears to change as the source moves with respect to the observer. In this sys- tem the satellites are the source of constant

frequency and - just as in the Loran-C

method - the receiving site must have a source of stable frequency.

The source of frequency on the satellite

is a precision quartz oscillator which may

at first seem surprising, since quartz os- cillators are significantly unstable in longterm. Quartz does, however, have excellent

short-term stability (see fig. 3) and the

oscillator is kept stable in medium and

long-term by being slaved to an atomic standard. Every time a TRANSIT satellite passes

within range of the Johns Hopkins University

its frequency is checked with corrections

made if it is out of tolerance. The Johns

Hopkins oscillators are also controlled, in long-term by the cesium beam standards that

comprise the time scale of the USNO.

Each TRANSIT satellite broadcasts a con- stant frequency and the coordinates of its

position in orbit, which are very well known.

At any given instant, the observed Doppler

shift depends on the angular coordinates of

the satellite with respect to the observer.

Thus, it has been possible to compile a catalog of computed Doppler data, or "Doppler

curves," for a network of points that covers

the entire earth. Under suitable conditions,

the system is able to, locate position to. '

.

^ within three to five meters'. To obtain his position, the observer feeds

three pieces of information to the computer:

1. ) the observed Doppler curve as the

satellite passes within range of reception;

2. ) data on the satellite position as broadcast by the satellite; and 3.) a rough

estimate of the observer's own position. The

computer then begins a series of iterative

calculations. It "looks" in its catalog to see what the observed Doppler curve would be

if the observer is, in fact, where he thinks

he is. Next it compares the actually observed Doppler curve with that in the catalog.

Usually a fairly large discrepancy exists,

and if it does, the computer makes a new guess as to the observer's actual position.

The comparison is again made with the proce- dure continuing until the discrepancy is re- duced to an acceptable level. Using the

data from a single pass of a satellite, pos- ition at sea can be determined to an accuracy

of .70 meters. Since there are three TRANSIT satellites

and each orbits the earth every 90 minutes,

it is possible to make about 30 observations

in a 15 hour period. If the position to be

determined is on land and not on sea, then

each "fix" can be used to improve the estimate. Thirty observations will yield a pos- ition accuracy (radius of the circle of

probable error) of about three to five meters,

and we are told that this is quite adequate

for geophysical purposes.

Since the data taken is of changes in frequency, and not phase differences, the re- quirements for the receiving oscillator are different than for the Loran-C system. What

is required is an oscillator that has good

short and medium-term stability. Good long- term stability is not required, so the re- ceiving site uses quartz or rubidium, and

not cesium oscillators (see fig. 3). To be

specific, the total observation time for a single pass of a satellite ranges from six

to 18 minutes depending on the observer's

geographical location, making the averaging

time (the t of fig. 3) of interest about

ten minutes (600 seconds).

An essential feature of the system is the

broadcast of the satellite's position,

which must be known to a high accuracy at any given time over an indefinitely large

span of time. This is only possible because

the orbits are well known and because the

USNO 'has an excellent ability to keep time.

The system is quite expensive. The total

equipment cost, for just one receiving site,

is estimated at $50,000 which does not include the cost of the satellites or the

necessary supporting facilities such as the

time keeping system of the USNO.

2.5.2.5 The Use of Date by the Shipping and

Boating Industry

To determine position at sea by celestial

navigation, the navigator needs to know his

angular position with respect to one or more prominent celestial bodies. He also needs

to know the date [14]-

The traditional answer as to what accu26
racy of date is needed is 0.5 seconds. (An error of one second in knowing date is equivalent at the equator, to about 0J2 miles in position.) But, the experience of the U. S. Navy is that - even with date accurate to one second or better - the accuracy of the

average celestial fix is only about six miles.

In other words, the inaccuracies of the usual

sextant reading predominate over the errors

in date. This means that an error in date by two or three seconds would, usually, not significantly degrade the fix.

Celestial navigation is an application

that needs date: just time-of-day won't do.

If a navigator is mistaken in what day it is by one day, he will be incorrect in his calculations by approximately four minutes, or

a position error of the order of 70 miles. I was told that standard time broadcasts are

used, almost without exception, to obtain

date. Clocks or watches are, of course,

also carried.

The commercial vessels that navigate the

open sea are a very important part of our economy although they represent only a tiny

fraction of the total number of vessels in

this country. In 1972, there were about

5.9 million registered vessels in this

country of which about 157,000 were large

enough to be safely taken into the open sea. Only a very small fraction of the total

navigate the open sea on a regular basis. I estimate the number of ships and boats that

commonly need to determine their position in the open sea to be 4,000 as a minimum and

50,000 as amaximum, not including military

vessels. Probably not more than one to two thousand of these are commercial vessels

(owner-operated for a profit).

Open sea navigation appears to be in a transitional phase between celestial navigation and electronic navigation as the pre- dominant means of^position location. The

commercially available electronic means are Loran A and C, Omega, and the TRANSIT satellites.

Evidently, almost all commercial operators

own Loran A or C equipment or both. Probably

50% of the ocean-going yachts carry Loran and/or Omega equipment. There have been

about 4000 nan-military Omega receivers sold.

I estimate there are at least 40 regular

users of the TRANSIT satellite service.

Despite the large amount of electronic

navigation equipment that has been sold, I would guess that at least half of the navigators (non-military) use celestial navigation

as their first-line position location method.

Nevertheless, I predict that by 1980, electronic systems will be the first-line method

used by the majority of open sea navigators.

3. IMPACT, STATUS AND TRENDS OF MEASUREMENT SYSTEM

3.1 Impact of Measurements

3.1.1 Functional, Technological and Scientific Applications

I shall reiterate the three basic functions

of a time standard given in section 2: 1.) to set a rate; 2.) to establish a time scale

for purposes of time-interval and simultaneity; and 3.) to relate distance to time.

Section 2.5.1.2.2 generalizes about the T&F

Flow Matrix and states the three most common functions that T&F performs for the major

end users: 1.) communications; 2.) pos- ition-location; and 3.) coordination.

Specific applications of T&F may be found in

sections 2.5.1.2.1 and 2.5.2. The following

is a more detailed elaboration:

- Local oscillators in TV sets (including

channel tuning)

- Rate and time-interval, and initiation

and termination of events in data processing

- Controlling the duration of physical

and chemical processes

- Transfer of accurate frequency to os- cillator manufacturers

- Labeling geophysical events

- Automatic turn-on/turn-off of appliances

- Timing therapeutic and observational

procedures for health care

- Billing for telephone usage

- Labeling the time of occurence of

important communications

- Aircraft collision avoidance (a potential application for a precisely

synchronized network of clocks)

The very great precision and accuracy of T&F standards give them a prominent position

in both science and basic metrology. A scientific application is one where there is no obvious technological benefit but where

the state of knowledge about nature is increased. Basic metrology is a technical

application that might alter the foundations

of the measurement system and/or alter the

present primary standards. The unit of timeinterval, the second, has a strong relationship to two other physical units, namely,

length and voltage.

The measurement of frequency and wavelength of certain stabilized infrared lasers

27
has progressed to the point that it is now feasible to derive the unit of length from

the frequency unit. This can be done by

using the present (or better) frequency and

wavelength knowledge to define a value for

the speed of light (a value which would also

be consistent with the present accepted

value). Thus, instead of two standards, one

each for frequency and length, there would

be only a frequency standard and the unit of

length would be based on it [15, 16]. Gen- erally speaking, frequency measurements are

being pushed to higher portions of the frequency spectrum [17]. These are frequencies

where the sources had been characterized by

wavelength measurements only. It is the re- cent presence of frequency-stabilized lasers

in this region that makes such frequency

measurements meaningful.

Frequency' is related to voltage via the

Josephson effect. The details of the relationship have been sufficiently worked out

so that in some countries, including the

U. S., the working standard for d.c. voltage

is the Josephson junction [18].

The present experimental relationship

between frequency and the two quantities

temperature and mass, is not as strong as for length and voltage. Nevertheless, the

potential importance to basic metrology is sufficiently strong to deserve mention. It has already been possible to use the

Josephson junction as a transducer between

temperature and frequency [19]. Certain

experiments in x-ray spectroscopy have sug- gested the possibility of defining the unit

of mass in terms of the unit of length [20].

If this should prove possible, then the

relationship between length and frequency

would allow mass to be defined in terms of

frequency. Taken all-in-all, there is a real possibility for a reduction in the total

number of independent primary standards nec- essary to form a realization of the basic

physical units.

The definition of the second in terms of a certain cesium transition and the relationship between frequency and wavelength (the

speed of light) express some fundamental

constancies of nature, namely, the equivalence

of atoms of a given species and the apparent

constancy of the speed of light. The study

of the clock transition in hydrogen^ is an- other careful test of the equivalence of atoms of a certain species. Generally

speaking, the whole field of spectroscopy,

which is highly dependent on frequency standards, is a study of the structure and stabil-

^An atomic or molecular transition used for

a time standard is often known as a clock

transition.

ity of atoms and molecules and of their

interactions with their surroundings.

Very-Long-Basel ine-Interferometry measurements, which require very stable frequency

standards, yield important information about

both the earth and its celestial surroundings. These measurements can be used to accurately determine the position of specified points on the surface of the earth, thus

detecting crustal motions which may have an important bearing on earthquake prediction

[21] . In Einstein's Theories of Relativity there

are two predicted effects that have a direct

bearing on time standards. The Special

Theory of Relativity states that two clocks,

running at identical rates when at rest, will

display different amounts of elapsed time

when in relative motion with respect to each

other. The General Theory of Relativity pre- dicts that two clocks, running at identical rates when sitting side-by-side, will run at different rates when they areac different

gravational potentials. Using atomic time

standards, a rough verification of both of

these effects has been obtained [22, 23].

Both effects are so small that a significantly improved test requires either a major

improvement in the time standards used or a change in the nature of the experiment. An- other experiment, scheduled to be performed

in 1975, will test the gravitational effect

using a hydrogen maser on board a rocket.

This should provide a test of the predicted

effect to a fractional accuracy of about

1 x 10"^ [24]. The accuracy of the present

test is about 1 x 10"^. An experiment under

consideration would use one of the two NBS primary standards (the second best) on board

an orbiting space vehicle to test the pre- dicted effect of relative motion (time dilatation) to an accuracy of about 1 x 10"^ of

the predicted magnitude. The present accuracy is about 1 x 10"^ [22]-

3.1.2 Economic Impacts - Costs and Benefits

To establish the value of a particular

institution or technology, it is tempting to ask what society would be like without that

institution or technology. For major institutions such as the telephone industry, or technologies such as T&F, such a question is meaningless. It is inconceivable to think

of completely eliminating the functions per- formed by them. There are always alternatives. There are always other people or groups of people and always other instruments

or configurations of instruments to perform

the original function. The functions may not

be performed identically, costs may vary, and costs versus benefits may be better or

28
worse. The question is often asked, "Are you

spending your resources optimally?" This is an exceedingly difficult question to answer.

It has two aspects. The first is to define

the costs and benefits associated with the

present allocation of resources. The second

is to compare the present cost-benefit

situation with that of possible alternatives.

It may often be possible to specify the

dollar costs of a given T&F delivery system.

It is usually more difficult to get agree- ment on quantifying the benefits of a given

system. Usually the cost-benefit situation

for alternatives is even less well known.

Often this is because nobody has tried the

alternative system. Until a person has determined costs and benefits for both the present

allocation of resources and alternatives he

is not able to say whether the present allocation is optimum.

It is presumptious for me to try to talk

about whether resource allocation in the

National Measurement System for Time and

Frequency - as a whole - is optimum, or even

to try to define costs and benefits for the

present system. I will not attempt either of

these things. The Flow Matrix of section

2.5.1 indicates the major users of T&F and

gives some indication of T&F's importance

to their internal functioning. Some very

subjective judgments are required to assess

the social value of the output of the major

users; even more difficult would be attempts

to attribute a definite proportion of that

value to the T&F input.

I will instead devote the rest of this

section to providing the reader with a general feeling that T&F is economically important. I will attempt this by doing two things. First, for some major institutions

that are known to make large use of T&F,

their total capital investment and yearly

revenue will be cited. Second, I will give

some examples of how much it costs certain

institutions to obtain a given time or frequency service. With regard to this second

consideration, presume that the dollar value

of the benefit of a given service is at least as large as the cost. This then est- ablishes a minimum value for the benefits of

that service to that institution.

General Capital Investment and Revenue

In 1973, the total capital investment of

the telephone and telegraph industry was roughly $100 billion and the revenue was around $27 billion [25]. Of this $27

billion about $9 billion came from longdistance calls [26]. For the aviation-aerospace industry , the

the present investment in just electronic

systems (airborne and supporting) is approximately $28.5 billion. Last year's revenue

for just the commercial aviation part of the

industry was about $12 billion [27].

In 1970, the capital investment of the

U. S. electric power industry was approximately $93 billion with revenue of $22

billion [28]. For the commercial shipping industry in

1971, the value of U. S. cargo ships was around $10 billion. The total value of the

goods shipped to and from the U. S. was $51

billion [29].

T&F Costs

The NCSL standards laboratories responding

to our questionnaire estimated a total capital investment in T&F equipment of $3.5

million. The total yearly operations costs were estimated to range between $540 thousand

and $940 thousand [11]- Using ten years for

total depreciation, I estimate the total

yearly T&F costs for these laboratories to be $1.1 million.

Estimating the annual local telephone call revenue and call volume respectively to be

$18 billion and 180 billion, one can derive

the yearly cost to the public to obtain the

time-of-day [25, 26]. From these numbers,

the average cost per local call is about

$0.10. For 2 billion TOD calls per year the

total cost would then be around $200 million.

(See sec. 2.5.2.2.) Since a TOD call is of

brief duration, a more conservative estimate

would be the cost of one message unit

(currently about $0.05 where this system of

charging is used) times the number of calls.

This gives an approximation of $100 million

per year.

I have made an estimate for the total T&F equipment cost for the new frequency equalization network for the FDM system of the

telephone industry. Using the notation in

section 2.5.2.3, with roughly $0.06 million

for the cesium atomic oscillator facility,

$2.1 million for the JFS sites, and $5.0

million for the PFS sites, the total is roughly $7 million.

In the aviation-aerospace industry , the

total amount of capital equipment directly

attributable to T&F is approximately $3.4

billion. The annual expense for maintenance

of this equipment, including calibration, is about $63 million [27]- For the commercial shipping industry there are typically three types of equipment on board for position location: two chronometers

per vessel costing $2000, receivers costing

$400, and electronic navigation equipment

costing $6000. The total expense per vessel

29
would be approximately $8,400 if there are nearly 1,000 commercial vessels that perform

open sea navigation [14], the total T&F equipment charge is about $8.4 million. (See

sec. 2.5.2.5.)

Assuming that 3,000 yachts use celestial

navigation equipment ancll>500 of these also

own electronic navigation equipment, a figure of $6.5 million may be assigned to the

sea-going yachting community for T&F equipment.

It would be nice to know whether the U. S. is becoming, relatively , more or less dependent on T&F. There are some indications that

it is becoming more dependent. The growth

of electronic position location activity is one indication. Another indication comes from the study of the communications industry.

As a part of the study of the National Meas- urement System for Time and Frequency, we

learned something about the general economic

features of the communications industry [30].

This study revealed that the relative expenditure of U. S. business for telephone service

approximately doubled in the period from

1947 to 1967.

3.1.3 Social, Human, Man-on-the-Street

Impacts

Clocks and watches vastly increase a per- son's ability to coordinate his activities

with those of others. That ability to coordinate is further increased by electronic

communications which are inherently dependent upon time and frequency technology.

Strongly related to telecommunications is public safety and the vast variety of job

opportunities and cultural activities available in industrial society.

The common telephone is probably the most

ubiquitous of all the uses of T&F. But less

sophisticated applications such as parking

and taxicab meters are also pervasive. Telecommunications enters in specific industries

such as aviation, rail transportation, and

shipping, and is vital to the national defense. A more restricted but very important

T&F application is for position location.

This application is essential to the shipping

and aerospace industries. Offshore oil well

drilling is another - and increasingly

important - application. The electric power

industry, while less dependent on T&F than

communications and position location, is also

an important user.

All in all, the ability to live in large

cities and to maintain a large per capita

material standard of living is significantly

(even if, abstractly) based on time and frequency.

If there is any brief statement that will

summarize the social function of time and

frequency, it is that they are the great

coordinators, the great organizers. If one

takes a general look at the historical

development of technology and its relation

to society, one sees a continually increasing organization of things and of people

[31]- Like it or not, if the material standard of living throughout the world is even

to be maintained, this level of organization

will probably increase. Time and frequency

will almost surely play an even greater part

in that organization.

3.2 Status and Trends of the System

The present status of the National Measurement System for Time and Frequency should

be viewed in several ways: through instrumentation (sec. 2.2 and 2.3), calibration

hierarchies (sec. 2.3 and 2.4), functions

that T&F performs (sec. 2.1 and 2.5), and

institutions that supply and use T&F (sec.

2.5).

Is the present National Measurement System

for Time and Frequency adequate? If the same functions could be provided for less

cost, or more service could be provided for

equal cost, then the answer would be no. In general, however, the problem is not so easily described.

Adequacy is a word that implies a strong

value judgment. I would prefer to avoid

using the term and simply attempt to describe

the probable changes in the system. Previously I have talked about technical aspects of

actual and probable changes; in this section

I will go into some of the socio-economic

forces behind these changes. The probable

changes lie primarily in three areas (see

sec. 2.5.1.2.3): 1.) the development of one or more networks of clocks maintained in synchronism to within 1 to 10 ys; 2.) a significant increase in the market for frequency equalization at levels of 1 x 10"^

and better; and 3.) a possible need for a more widespread time calibration network at

an accuracy of about 0.1 seconds. This

possible need for better time-of-day calibration was discussed in section 2.5.1.2.3.3

and only the first two areas require further

discussion.

My predictions for change are based on

two types of data: 1.) detailed studies of

certain industries; and 2.) a polling of

expert opinion about the probable future of T&F technology (Delphi . Study). The four

industrial studies examined are of the telephone industry, the electric power industry,

the aviation industry, and industrial and' other standards laboratories.

The Delphi Study was performed under the

30
auspices of the Technology Forecasting and

Assessment Subcommittee of the Communications

Group of the IEEE. Appendix A. 2 includes the

questionnaire and background information sent

to each of the prospective participants. A major reason for this approach is that socioeconomic forces are likely to be extremely

important in determining what changes actually occur, and I felt this was a good way of

attempting to include these considerations.

[32].

The questionnaire was sent to each of 107

prospective participants equally divided

between seven sectors:

1. ) Telephone industry

2. ) Communications services other than

telephone

3. ) Navigation - transportation industry

4. ) Oscillator manufacturers

5. ) Communications equipment manufacturers

6. ) National standards laboratories

7. ) Science

The questionnaire consisted of three sets of questions. The first two dealt with

eight very specific T&F resources that might

come into existence in the future. In the

first set the participants were told to assume that each resource would be available.

The task here was to estimate the probability

of significant use of each resource. (The

results of question set one are given in fig. 5.)^ The second set took a step backwards and assumed that none of the eight

resources actually exist now. The task for

this question set was to estimate how much

"pressure" the participants' sector would

exert to bring them into existence. The

third set dealt with general technologies

(each dependent on T&F) and their probable

future importance to the sector in which the

participant was employed.

The major motivation for the second set was to partially check the validity of the answers to the first set. The result was usually a very strong positive correlation.

The primary purpose of the third set of

questions was to check on my prediction that

there is likely to be a very extensive alldigital telecommunications network in the

U. S. by 1980-1985.

^The first column ("Negative" Responses) is formed by adding the "Virtually Impossible"

and "Relatively Unlikely" responses. This

is done for each of the years 1980 (cross

hatch) and 1985 (solid). The "Positive"

Responses column is formed in a similar way. For either of the years, the reader should

compare the relative sizes of the "Positive"

and "Negative" responses.

To give the reader a feeling for the eco- nomic rationale behind the first two areas of probable change, I will examine the four

detailed industrial studies at lenqth.

The forecast of a widespread network of

clocks, synchronized somewhere in the range

of 1 to 10 ys, is based in large measure on

a study of the telephone industry [12].

This prediction, in turn, rests on the fore- cast of a widespread, all-digital, telecommunications network.

There are some large economic advantages

to digital as opposed to analog transmission,

but to adequately realize these advantages,

the switching offices (at least the major

ones) must operate digitally. In reference

12 (which is quite detailed) I show that

there is already a powerful trend toward

digital transmission. In addition, there are advanced plans to replace a major part of the

analog switching network with digital switching. The implementation of these switching

changes will begin to occur in 1976. Both

the transmission and switching aspects of

the all-digital network have timing requirements. But, does this mean that a network of

synchronized clocks (to 1-10 us) is economically justifiable? I believe that there are

at least three reasons to think that it is.

First, such a system would make the access

to an all-digital telephone network much

easier, probably proving economical for the

telephone industry in the long run. In addition, the actions of the federal govern- ment in recent years indicate that the telephone industry will probably be forced to permit greater access to its (the telephone

company's) system. If so, the timed network

would facilitate this access. Second, one major telephone system (Bell-Canada) already

has a small version of such a system in operation. Third, there was a strong consensus

(displayed in item 7 of fig. 5) in response

to the Delphi Study that such a system would

be put to significant use. Another important supporting factor is the potential use of such a system by the military. One group

within the Defense Communication Agency

feels that such a timed network would be

very valuable. Within the continental U.S..

the telephone industry provides the bulk of

military communications, a possible factor

in encouraging the telephone industry to install such a system.

The telephone industry probably has the

greatest motivation and the most resources

for setting up an extensive network of synchronized clocks. This is not, however, the

only means by which such a network could

come into being, and in fact, there already

exists a network of clocks synchronized to better than 1 ys. This network is operated

31
[For details about the interpretation of this figure

see Appendix A. 2]

"NEGATIVE" RESPONSES"POSITIVE" RESPONSES

VIRTUALLY

IMPOSSIBLE RELATIVELY

UNLIKELY RELATIVELY

LIKELY

VIRTUALLY

CERTAIN

RESPONSE {%)

10 _l_

30

I

I 7-1

E

RESOURCE 40 _J

FREQ REPEATABILITY

FREQ EQUALIZATION

TO 1x10''^- 15 MIN AVG $200/STATI0N

RESPONSE

10

I 20 _L_

30 40 _l

Ok

FREQ EQUALIZATION

TO 1x10"'''- 10 DAYS AVG $10k/STATI0N

SYNC TO 30 ns lilB

10 MIN SIG RECOV llljlill TIME <;iOk/STA - Hi|^H~ ANYWHERE IN USA

E

E

FREQ REPEATABILITY

1x10"'° - $lk/UNIT

FREQ REPEATABILITY

1x10"'*- «15k/UNIT

FREQ DRIFT LESS THAN lxlO"'/DAY $100/UNIT

SYNC TO 2 us

1 MIN SIGNAL RECOV

TIME - S200/STA

ANYWHERE IN USA

1980

Figure 5. Responses to set 1 of the Delphi questionnair

32
by the Department of Defense and is synchronized by the Defense Satellite Communications

System. The satellites obtain a time reference from the USNO. The system contains a total of about 33 clocks, with 9 in the

continental U. S., the rest spread around

the world.

In conjunction with NASA, the T&F Divison

of NBS is planning to provide a timing ser- vice bas&d on satellite broadcasts and cov- ering the entire U.S., beginning about 1979. Present evidence indicates that the service

will allow time to be recovered on the ground

to an accuracy of a few microseconds. The cost (in 1975 dollars) will be about $200 per site.

It now appears that two other major industries would make use of the 1-10 ys network

if the clocks were strategically available.

The electric power industry has one present

and one potential use for such a system. The

present use is for fault location: a clock

accuracy of 1 ys would permit location of a fault to within a thousand feet. A net- work that was synchronized to the order of

10 to 20 ys would allow the measurement of

phase angle of the current and voltage to about one degree, possibly capable of pro- viding better system control than the present

method. The previously estimated cost (for

the NBS satellite services) of $200 per station would probably be economic for the phase

angle application and maybe for fault location.

The aviation industry is in need of an improved but low-cost air-collision avoidance

system. One such system using a network of

timed clocks has been proposed which requires

a timing accuracy of 1 ys or better [33].

One final application is the accurate

location of position on the surface of the

earth. Section 2.5.2.4 describes a position

location system that makes use of trans- mitters carefully controlled in phase. These

stations require phase control to about

0.1 ys. However, a widely available, low- cost capability of a few microseconds, such

as provided by the NBS satellite service,

would be a welcome complementary system.

Time dissemination systems and position

location systems are intimately related, re- lying on precisely controlled phase of their

transmitter(s) . The National Bureau of

Standards has attempted to show that a pos- ition location system can do double duty,

serving sometimes for time dissemination as well as position location. Some systems have

very wide coverage, such as Loran C and Omega,

and are almost always federally owned and

operated. In such cases, it is more economic

for the taxpayer, to design an easily usable

time signal into the system right from the

beginning.

In summation: there are several major

organizations which would probably use a widespread 1 to 10 ys timed network if it

existed, but the telephone industry is the most likely to set up such a system. The

planned NBS satellite service will be

sufficiently low in cost and easy to use that

it should attract a great number of users. Consider now the probable market for an improved frequency equalization capability.

The NBS stations WWV-VH provide such a service at the 1 x 10"^ level as do a few

other standard frequency broadcasts. The

service is widely available, easy to use, and at the fairly low cost of about $250 per

site. At a level of 10"^ and better, the costs go up to a little over $2000 per site,

and at about 1 x 10"^ the amount of operator

effort and skill begins to rise sharply.

I have identified six areas where frequency equalization to better than 1 x 10"® but

probably not better than 1 x 10"^° is needed:

1. ) The FDM system of the telephone

industry needs about 1 x 10'^°(see

sec. 2.5.2.3).

2. ) The Dataphone Digital Service of AT&T

needs 2 x 10"^ or better [341

3. ) At least 70 of the NCSL-member standards laboratories need better than

1 X 10'^. Unfortunately, we don't

know how much better. However, we

do know that 17 laboratories in this

group own either cesium or rubidium

standards or both.

4. ) According to reference 33, that

version of an air-collision avoidance

system, ACAS, needs 1 x 10"^ Unlike

the previous three items, this sys- tem is hypothetical. It has been pro- posed to the FAA but is not under

construction.

5. ) If the more stringent specification

on TV broadcasts now being considered

by the FCC goes through, the requirement will be about 1 x 10'^ (see

sec. 2.4.4).

6. ) The portable units in the military's

Global Positioning System (GPS) have

a requirement in the range of

1 X 10"« to 1 X 10'i°.

Each needs a method requiring a very small

amount of operator time with five of the six

needing one requiring little operator skill.

Five of the six could use either a dissemination technique or a low-cost oscillator

that is sufficiently accurate. Because of

the military need for portability, the GPS

and certain other military applications

would need an accurate oscillator. The TV "color burst" system, which has been exten- sively developed by the T&F Division of NBS,

33
is technically suited to meet the needs of

the first five areas. It has been shown to yield frequency comparison (which is basically equivalent to equalization) to a few

parts in 10^ \ with only 15 minutes of

averaging time. The cost per site is presently about $500. Items 1 and 5 in figure 5 give additional support to the idea that

frequency equalization needs at this level

of precision or higher are likely to exist.

I claim that the market exists today in areas one through three.

It is important to predict the size of

the potential market in these six areas. For

the first, I have already estimated 1,000

(see sec. 2.5.2.3). The second application

could probably use about 200 by 1977. A guess for the third area is 30. If the

fourth application came into existence, the

requirement would exist in each of about

2,300 commercial jet airliners and about 100

ground stations [27]. In the fifth area, there are presently over 920 commercial TV broadcast stations and each is a potential

user. The sixth area is poorly determined,

but potentially is extremely large: NBS personnel estimate the total military nav- igation market to be about 50,000, most of

which would be in the GPS system.

There appears to be a potential market

for a 1 X 10"^° to 1 x 10 "dissemination"

system at a cost of $1,000-2,000 per unit

of 4,500 ._ That for an oscillator accurate

to 1 X 10 ^° at about the same price should

be over 50,000.

Finally, major needs for frequency equalization beyond the 1 x lO"-'" level will

probably be a part of a need for time syn- chronization (see sec. 2.5.1.2.3.2). If the

timed network discussed in this section

comes into existence, requirements for frequency equalization to about 1 x 10"^^ will

probably accompany it, existing at up to 2.000 sites by 1985-1990.

4. SURVEY OF NBS SERVICES

4.1 The Pasti

4.1.1 Developments up to 1923

In 1911 the development of radio technology had come to the point where NBS was

"^The history of NBS T&F activity given above

is drawn in large part from the very detailed and excellent history written by

Mr. Wilbert F. Snyder of NBS. The information used here was taken from chapter 8 of

Mr. Snyder's history of radio work at NBS which will be published sometime in 1977 and

is listed here as reference 35.

asked to perform its first wavemeter calibration. (For many years the measurement of

frequencies associated with radio trans- mission was performed by devices known as wavemeters. It wasn't until 1923 that devices of this type came to be known as frequency meters. ) This initial calibration

was performed with a resonant LC circuit.

For the first few years, the calibration of

the circuit was in terms of low frequency

inductance and capaci tance (L and C) measurements made upon the inductor and the capacitor. By 1918 the L and C of the wavemeter

were being determined by calculation. The

accuracy of the total measurement was no better than about 1 x 10"^ at this time. The

accuracy was established by comparison with

the rotation rate of the earth about its axis,

this being the accepted definition of frequency until 1956. The calibration of the LC wavemeter with respect to the rotation of the

earth is circuitous but interesting: the

frequency of the resonant circuit is given by

the formula f = 1/(2 tt/lT). Both the L and C were expressed in terms of their geometry and

absolute dimensions. This relationship to length is then convertible to the inverse of

time interval (i.e. frequency) via the invariant relationship between the wavelength

of an electromagnetic wave and its frequency - the speed of 1 ight.

One of the basic problems of determining

the accuracy of a given frequency measurement

has always been that of relating the frequency

to be measured to the prevailing def ini tion

of frequency. The difficulty is that they

are often different in frequency by orders of

magnitude. For example, the frequency of the

rotation of the earth on its axis is about

12 micro hertz. A typical resonant frequency

for a tuning fork is one kilo hertz. Thus,

the frequency ratio is about 10®. In practice

what usually happens is that one or more

transfer standards are interposed between the

device to be calibrated and the device which

is the physical realization of the definition

of frequency. A good example of this occurs

when, in later years, the LC wavemeter was calibrated by a tuning fork.^ In this in- stance the tuning fork was, in turn, calibrated by a pendulum clock and finally the

pendulum was calibrated by the earth's rotation. This calibration and apparently some basic limitations of the LC circuit, limited

the accuracy of the LC wavemeter to about

1 X 10 \ despite the fact that the accuracy

of calibration of the tuning fork was a little

better than 1 x 10"\

^By 1917, tuning forks were being used as frequency standards by the Sound Division of

NBS. By 1922, these devices were also used

in the calibration of the LC wavemeter.

34
The problem was the same in measuring

time because the period of one rotation of

the earth (one day) is too long for many hu- man applications. A period of about one s-ec- ond is a more appropriate base unit . What

was needed was a "flywheel" which could pro- vide a shorter base unit but could still be

calibrated in terms of the earth's rotation.

A practical flywheel is one which repeats

its basic behavior - "motion" - for at least

one day. Pendulums served this function

very well for about two hundred years (see

fig. 1).

Thus, both frequency and time measurement

are faced with the fact that the frequency

(period) of the device to be calibrated is usually grossly different than that of the source of calibration.

Today, the definition of time interval

(and therefore frequency) is in terms of a cesium atom transition at about 9.2 x 10^ Hz. Yet the problem is much the same. A useful

base unit of time interval is now about 10^°

times longer (instead of shorter) than the

definition in terms of cesium. Also, many

Important frequency applications are for

frequencies much less than 9.2 x 10^ Hz. Thus,

frequency "dividers" must be used to translate the frequency of the primary standard

to lower frequencies and longer time intervals, and frequency multiplication must be

performed to measure those frequencies that

are higher than that of the primary standard.

The LC wavemeter was to serve as the NBS standard for radio frequency for about

eleven years, from 1918 to 1929, although by

1920, quartz crystal oscillators - which

would replace the LC wavemeter - were becoming of technological importance. The real push for measurement of radio frequencies

did not come until the early 1920's with the

advent of radio broadcasting: closely

associated with this was the development of

quartz oscillator technology.

The first NBS experience with crystal

oscillators came in 1920 with a requirement

for calibration of four of them. These oscillators were the first of many sent to NBS by

Professor W. G. Cady of Wesleyan University.

In 1923, NBS calibrated seven of Professor

Cady's oscillators, ranging in frequency from

14.5 kHz to 763 kHz. These same oscillators

had also been studied by six other laboratories, five of which were in Europe. The

general agreement among laboratories was of

the order of 1 x 10"^ - quite an achievement

considering the early stage of quartz technology and the difficulty of the measurement.

4.1.2 Frequency and Time Standard Develop- ment in the Period 1923 to 1947

Including the Activities of NBS Station WWV

By 1924, NBS was studying quartz crystals

for use both as standard frequency oscillators

and as a means of controlling the trans- missions of radio broadcast stations. This

work was sorely needed because, by 1922,

there were 570 U. S. broadcasting stations

operating within a 1000 kHz band. At this

time, the ability of a broadcaster to control

the frequency of his transmission was insufficient. A real problem existed in reducing broadcast interference and NBS took two basic approaches towards its solution. The

first was the development af frequency refer- ence test sets, and the second was the establishment of a standard frequency broadcast

station. This station, now located in Fort Collins, Colorado, whose call letters were (and still remain) WWV, went on the air

March 6, 1923.

By late 1925, NBS had developed a broadcast frequency test set which could be used

in the field, an oscillator with a quartz

crystal as its resonant element. In February, 1927, the Congress created the

Federal Radio Commission with the hope of

reducing interference between broadcast

stations. This organization, renamed the

Federal Communications Commission in 1934,

specified a tolerance of 500 hertz on the

carrier frequencies of broadcast stations.

The National Bureau of Standards was given

the responsibility of checking whether this

specification was being met. The NBS studies

into the temperature stabilization of quartz

crystal oscillators (beginning in 1927) re- sulted in helping to meet this responsibility

to the Federal Radio Commission and in improvement in the NBS frequency standard.

In February, 1927, NBS organized a conference among U. S. laboratories for the purpose

of further development of quartz oscillator

frequency standards. Three of the eight

laboratories involved (Naval Research Laboratory, Bell Telephone Laboratory, and NBS)

began a comparison of seven quartz frequency

standards. By 1929, this resulted in oscillators and measurement techniques showing a frequency accuracy of 1 x 10' . Quartz oscillator technology has been

fundamental to the telephone industry for over 50 years. Indicative of this is the

fact that NBS contracted with Bell Laboratories to construct four temperature-controlled,

100 kHz quartz oscillators to form the heart

of a National Primary Standard of Radio Fre- quency. These devices were delivered to NBS

in August, 1929. The technology had developed

to the point that frequency differences

between the oscillators as small as 1 x 10'^

could be detected.

A submultiple output of 1000 Hz from the

frequency standard system was used to drive

35
a clock synchronized to mean solar time from

the USNO via radio broadcast. One very

important result of this cooperation with

the Observatory was that the quartz frequency

standard system was found to be drifting at the rate of about 1 x 10"^ per month.

Even with this limitation in long-term

stability, quartz oscillators had become of

great importance to radio broadcasting. In particular, they served both as a means of

calibration and as a control of station WWV.

It is important to trace the development of

this station along with quartz oscillators

and, later, atomic oscillators with which it

is so closely associated.

By 1926, the development of quartz oscillators and the general development of frequency metrology had resulted in several

broadcast stations that could be used as reference standards. In that year, for

various reasons, NBS suggested the termination of the WWV broadcasts, which caused such

serious objection from WWV's users the idea was abandoned. Moreover, the termination

of the broadcasts has never been seriously

considered since.

Initially, WWV was located on the Bureau grounds in Washington. In January, 1931, the

station was moved to College Park, Maryland

just outside of Washington, D. C. In Dec,

1932, the station was moved to Beltsville,

Maryland where it remained until 1966 when

it was relocated to Fort Collins, Colorado.

In 1932 the broadcasts were on just one

carrier frequency, 5 MHz. By 1937, the

station operated on carrier frequencies of

5, 10, 15, and 20 MHz. The carriers were modulated so that they delivered standard

audio frequencies of 440 and 1000 Hz and

time "ticks" spaced one second apart. The

carrier frequency accuracy was now about

2 X ^o^

In June, 1944, a cooperative program was begun with the USNO when the time signals of WWV were synchronized with theirs and standard time was broadcast at five minute intervals in telegraphic code. By 1947, calibration with mean solar time via the USNO

showed that WWV was broadcasting with a carrier accuracy of 2 x 10 ^ . In 1950, voice announcements of time of day were begun.

By 1952, the National Standard included

six crystal oscillators plus eight quartz

crystals used passively as resonators. Fre- quency comparisons were made daily between

all the units to a precision of about

1 x 10"^°. The stability of the National

Standard was now at a level which made the

daily fluctuations and longer term fluctuations in the rotation rate of the earth

easily discernible.

The quest for accuracy is a search for

environmental independence. In a general

sense, it is a seeking for primary standards

that are based on fundamental constants of

nature and not upon artifacts of humanity.

Since accuracy can never be any better than

precision, part of the search for accuracy

has also been one for stability. Thus,

quartz oscillators replaced the LC wavemeter

partly because they permitted a higher pre- cision of comparison. The pendulum clock,

because it could act as a stable flywheel,

allowed the translation of the definition of

time interval, given in terms of the earth's

motion, into a working standard. Quartz

oscillators served the same function as the

pendulum clock. As the technology of quartz

oscillators grew, their stability improved

sufficiently (better than 1 x 10'^ for one

day's averaging time) to detect nonuniformity of the earth's rotation rate. Thus,

although the earth's rotation has the desirable property of not being a human artifact,

it lacks the invariance with time that is so devoutly sought in a primary standard. Even though the ability to keep stable time was improving rapidly because of the use of

quartz oscillators, the situation was un- desirable from the point of view of a primary

standard. The stability of quartz oscillators

averaged over a few days' time, was better

than that of the earth's rotation rate. On the other hand, the earth had the naturalness - the lack of human intervention - which quartz

lacked. This brings me to the last facet of

the story: the development of atomic frequency standards.

4.1.3 Atomic Standards and Further Improve- ments in the Broadcast Services

Fundamentally associated with the development of atomic frequency standards was the

development of the technology of microwaves.^

Microwave technology developed rapidly during

World War II and was closely associated with

radar. As part of this effort, NBS, in 1944,

undertook the development of a microwave frequency standard. The project resulted in a standard which was accurate to 1 x

10"''. Work of this type gradually built up the

technology - including frequency multipliers

and mixers - that was essential to the

development of atomic frequency standards.

In 1879, Lord Kelvin, using a suggestion

by James Clerk Maxwell, proposed the use of atoms of hydrogen and sodium as natural

standards of frequency and length. The first

"atomic" frequency standard, however, was based not upon an atom, but upon the ammonia

molecule. Important in this development were

the microwave spectroscopic observations

that were performed at the University of

Michigan around 1934. The ammonia standard,

based upon the absorption cell principle [36], was used for the first time as a clock on

^The microwave frequency range lies, roughly , between 1 GHz (10^ Hz) and 40 GHz.

36
August 12, 1948. This clock demonstrated a stability that was greater than that of the

rotation of the earth on its axis but not quite as good as the earth in its orbit

around the sun. The absorption cell technique was the first

to be used in an operational atomic clock.

Many people felt, however, that an atomic

beam technique [36] would produce a device

of greater stability and accuracy. As early

as 1945, Professor Isador Rabi of Columbia

University suggested the beam technique for

use as a frequency standard. In the summer

of 1949, a project to exploit the beam technique for a frequency standard was begun at

NBS. The atom selected was cesium and

Professor Polycarp Kusch of Columbia University was employed as a consultant. A year

earlier, Professor Charles H. Townes (also

of Columbia University) was employed as a consultant in a project to study the micro- wave spectra of gases and sol ids

The physics and engineering considerations

that resulted in the present state of the art in atomic frequency standards are beyond

the scope of this work. The reader who is interested in this fascinating subject can profit from reading chapters 3,4,5,6, and 7 of reference 4 and, also, reference 13. Station WWVH is one of the three NBS standard time and frequency stations. Located

in the Hawaiian Islands, it began broadcasting

in 1948. Its broadcast format is essentially

that of WWV and the station is designed to provide T&F service over much of the Pacific

Ocean and surrounding lands. In 1954, most

of the radio activities of NBS were moved

to Boulder, Colorado: among those were the

National Standard for Radio Frequency (the

ensemble of quartz oscillators), the ammonia

clock, and the first cesium beam frequency

standard. Even though the quartz ensemble

was now located in Boulder, it was still used

to monitor the broadcasts of WWV 'near Washington. This monitoring-at-a-distance

was not new to NBS. A related task had been

performed earlier for the Federal Radio

^It is interesting that three of the people

who have worked on the NBS frequency standards

and spectroscopy activities later won Nobel

prizes in physics. Walter H. Brattain, who

worked on the temperature stabilization of

quartz oscillators in the late 1920's, won

the 1956 prize for the discovery of the

transistor effect. Polycarp Kusch won the

1955 prize for the determination of the magnetic moment of the electron. Charles K. Townes won the 1964 prize for work demonstrating the principles of the maser.

Commission and since 1948, we have been monitoring the carrier frequencies of WWVH. One

result of this monitoring-at-a-distance was

the establishment of the third NBS broadcast

station, WWVB. Measurements of the WWV broadcasts showed that the received signal could

be in error in frequency by as much as

4 X 10'^. This error resulted because of the

Doppler shift from the moving ionosphere [8].

Station WWVB, operating at the much lower

carrier frequency of 60 kHz, was set up to reduce this effect. The initial broadcasts

originated from the Boulder Laboratories of NBS and began in 1956. Both WWVB and WWV were later moved to Fort Collins, Colorado,

50 miles northeast of Boulder.

The first NBS cesium beam frequency standard was in operation by 1958 as the NBS working standard of frequency and became known

as NBS-1 . It was used to study the frequency

stability of the WWV broadcasts. By spring,

1959, a second NBS cesium beam standard

was in experimental operation, known as NBS-II. NBS-I and NBS-II were i ntercompared

and found to agree in frequency to about

1.5 X 10"^^, meaning that devices now existed

which provided the physical basis for a new definition of frequency. From 1956 to 19577 the

official definition of frequency was based on the rotation of the earth about the sun (the

ephemeris second). The precision with which

this motion can be determined - and therefore,

its accuracy - is about 1 x 10 . Thus

there was evidence that a definition of the

second based on the cesium atom could be at least 100 times better than that based on the

earth's orbit about the sun. The way was open for basing frequency on the microscopic

world of the atom instead of the macroscopic

world of the earth.

On January 1, 1960, NBS-II was officially

adopted as the U. S. Frequency Standard. The

broadcast stations WWV, WWVH, and WWVB were

now being controlled as well as monitored by

NBS-II. (Commercial cesium beam standards were used at the stations themselves and

NBS-II was used to correct long-term errors. Construction of a third cesium beam standard - NBS-III, with a demonstrated accuracy of a few parts in 10^^ - was begun in 1959, becoming the new U. S. Frequency Standard in

September, 1963. By now, a time scale ms

in operation at the Boulder Laboratories,

based on an ensemble of commercial quartz

oscillators. The rate (frequency) of

this ensemble was regularly calibrated

by the NBS primary standard. In April, 1963,

the time scale broadcast by WWV, by setting

a quartz clock in Boulder and transporting

it to the WWV transmitter in Maryland, was brought into synchronizm with the Boulder

time scale to within 5 ys. The WWVB trans- mitter was moved to Fort Collins, Colorado
in July, 1963. Its carrier frequency was controlled by NBS-III to approximately

2 X 10"^ ^ On November 30, 1966, station

WWV was shut down at its Maryland site and

transmission was begun at Fort Collins,

Colorado.

In October, 1967, the 13th General Conference of Weights and Measures (CGPM) officially defined the second in terms of a transition frequency of cesium. On June 30, 1972,

the NBS radio stations (as well as many other

standard T&F stations around the world) made

the first "leap second" correction to its

time broadcasts, an action recommended by the

International Radio Consultative Committee

(CCIR) to compensate for the fact that a time

scale based on the atomic definition of the

second runs at a rate some 3 x 10'^ faster

than that based on the rotation of the earth on its axis as of 1972.^

The T&F Division of NBS continues to work

at both oscillator development and the means

of dissemination by which the signals generated by those oscillators can be transmitted.

NBS-III has been replaced by NBS-4 and NBS-5,

both based on the cesium beam technique and

demonstrating an accuracy of about 5 x 10'^^

and 1 X 10"^^ respectively. They are both

used in calibrations of the NBS time scale.

The ensemble of eight commercial cesium

beams that currently makes up the NBS time

scale is also used to control the broadcasts

of the NBS radio stations. The NBS time

scale is presently synchronized to that of

the BIH to within one microsprond.

Since the frequency standards activity

has been moved to Boulder, studies of the

thallium and hydrogen atoms and the ammonia

molecule--as applied to frequency standards--

have also been conducted. Work with the

thallium atom and the ammonia molecule was terminated several years ago; but work with

hydrogen continues, showing promise for a very useful secondary, if not a primary,

standard. In recent years, work in the T&F

and other divisions of NBS on the molecular

stabilization of lasers has shown promise

for frequency standard applications. Inves- tigations of short-term stability are important in several applications of time and

frequency standards, including the primary

, standard. To this end, development of quartz

oscillators still continues; and a new project,

the superconducting cavity oscillator, is underway.

^I mentioned that some applications, such as celestial navigation, must have apparent solar

time, but there are some applications that

depend upon the stability of atomic time. See Section 2.5.2.5.

Research and development in dissemination

techniques is also being emphasized. Over

the years, division personnel have studied

the characteristics of the Loran-C and Omega

systems, as well as dissemination via satellite and 1 ine-of-sight microwave (TV) systems.

The satellite and TV projects are active at the present time. Results from the satellite

project indicate the possibility of at least

a partial replacement of the NBS broadcast

stations by 1980. Unpublished information

available today indicates that a standard

T&F broadcast via satellite could be operated

at a significant cost reduction over the

present broadcast services. The quality,

too, shows promise of being significantly

improved.

The TV technique (which makes use of the

rubidium frequency standards used by the

major television networks) will probably

prove to be an important substitute for some

of the frequency services of the NBS broad- cast stations. The technique can be particularly useful to those who needgfrequency _ii

accuracy in the range of 1 x 10" to 1 x 10 One very important application of the technique is in the slaving of stations WWV and WWVB to the NBS time scale. With this method,

the signal as broadcast from Fort Collins, is

in synchronism with the_^ime scale to within

30 nanoseconds (30 X 10' s). It also allows

a very accurate frequency comparison - in long-term - with the NBS primary frequency

standard J Comparisons to the order of

1 X 10" have been achieved. for averaging

times of about one week.

4.2 The Present: Scope of NBS Services

4.2.1 Description of NBS Services

The Time and Frequency effort of NBS, as

it is presently constituted, is mainly located in two sections. The section responsibl

for broadcast services and dissemination

research is called the Time and Frequency

Services Section. The other section, Fre- quency-Time Standards, is responsible for

the primary frequency standards, the time

scale, and research towards new standards

and measurement methods.

In Fiscal Year 1975 there were 15 major

projects active within these Sections. It is useful to classify these projects in terms

of the first six of the "outputs" discussed

in section 2.5.1.1. Using this description

to categorize the outputs, the FY 75 pro- jects are distributed as follows:

38
Category # of Projects

A. Source 1 B. Signal 4

C. Receiver 3

D. Dissemination Means 1 E. Publish 2

F. Consult 4

Seven of the fifteen projects are significantly described by two and not just one

output. In those cases I have estimated which

one of the two outputs best describes the

project and used that description.

Describing the Sections in terms of outputs versus dollars spent (in FY 75) results

in:

Category FY 75 $

Source 386 K Signal 890K

Receiver 546K

Dissemination Means 35K

Publish 135K

Consul

t

49K

TOTAL 2,041

K

A significant part of the effort that goes

into the categories of Source, Receiver and

Dissemination Means, is motivated by a desire

to maintain or improve the quality of the

signal at the user's site. Moreover, when

calibration is performed at the site of the

primary standard (or time scale) the Source

and the Signal become indistinguishable.

Time and Frequency Division personnel

currently participate in the following T&F standardization organizations:

- Department of Defense Coordination

Committee for General Specifications

of Crystal Oscillators

- IEEE Administrative Committee

- IEEE Technical Committee on Frequency

and Time, Subcommittee on Frequency

Stabil ity

- IEEE Technical Committee on Frequency

and Time, Subcommittee on Time

- CCIR Study Group IV

- T&F Subcommittee of Federal Telecommunications Standards Committee

- CCIR Study Group VII

- lAU Com. 31

- URSI Com I - CCIR, International Delegate to Plenary

Session of Study Group VII

- Consultative Committee for the Definition

of the Second

At any given time, some Division personnel are likely to be involved in trying to help

solve a time or frequency problem for some other organization or group. This may be

only consultation or it may be an experimental

or theoretical project. At the present time

there are two such activities: 1.) consultation and experimental effort for industry

and the military on atomic oscillators to be

used with the Global Positioning System (see

also sec. 2.5.1.2.3.1); and 2.) consultation

with U. S. Navy Standards Laboratories about

the use of the TV frequency-equalization

technique. [38]

In describing the realized measurement

capabilities of the Division, I will restrict

the discussion to that of the performance of our several sources. The reason is that the

quality obtainable from our broadcasts strongly

depends on the user's circumstances. The

quality finally obtained will depend on at

least four factors: 1.) the user's location

with respect to the transmitter; 2.) the

quality of his receiving equipment; 3.) his

skill; and 4.) the amount of time he is willing to spend averaging the signal.

The experimental and theoretical ability

to characterize frequency standards has grown

tremendously over the years as has the quality

of these standards. The NBS has played a significant part in this development. Advancements in the state of this science have been

particularly great since the introduction of

atomic oscillators. Referring to figure 3,

the reader will notice that no one type of

oscillator can be said to have the highest

quality. Quality depends upon the averaging

time, T, in which the user is interested.

For example, in the range 1 1 x £ 10^ seconds,

the superconducting cavity oscillator is superior to any other known type of device.

On the other hand, for averaging times of

months and years, this type of oscillator

would probably not be as good as the cesium

device. I say probably, because such experiments have not yet been tried.

In figure 6, the o (t) versus x curves of

four types of devices-^in operation at NBS are shown. ^ The dotted curve shows the

proven capability of our measurement system , specifying the quality of the best oscillator

which we could now measure vf an oscillator

of such quality existed.

To our knowledge, no other measurement

system exists which is the equal of this over the range indicated. The four curves

shown are good approximations of the state- of-the-art for each of these types of devices.

^Actual ly, the superconducting cavity oscillator is not yet in operation and the curve

shows only our expectation of its performance.

The device should be operating within six

months to a year.

39
Over the ranges in which each type of device

is superior, we know of no other type of device which is better. It is important to reiterate that the present definition of

time interval (frequency) is in terms of a certain transition of the cesium atom, which

is therefore the basis for frequency accuracy.

(The reader may wish to reread the discussion

of accuracy in sec. 2.3.)

The primary standard, NBS-5, with estimated

accuracy between 1 and 2 parts in 10^', is our physical realization af the definition of

frequency. It is essentially equal in accuracy to the best two other primary standards

in the world. (See sec. 2.2.2.)

t(s)

understanding of the device and helps in its

optimization [5]. A second occasion is for

frequency multiplication of very high order,

such as that between the microwave and infrared ranges, already proven to be of great

importance to metrology [16, 17]. When the

multiplication is of high order, measurements

of Sy(f) of the lower-frequency oscillator

are most useful [39, 40, 41].

/* /* _/ /

/

/

/

/'/

/

y

/

/

/ /

^"^ PHtSEHT LIMIT OF ^•^ MEASUREMENT SYSTEM

, 1 1 1 _| u.

Fig. 7 Frequency-domain behavior of NBS sources and measurement system

Fig. 6: Time-domain behavior of NBS sources

and measurement system

Consider now the frequency-domain stability

measure, Sy(f). For Fourier frequencies, f,

beyond about 100 Hz, our capability is not as good as it needs to be. The upper two curves

of figure 7 show the range of quartz oscillator stabilities that we are often asked

to measure. Beyond about 100 Hz, for the

best oscillators, our measurement system is

a limitation. The oscillators were at least

as good as our measurement capability and

perhaps better. [43,44]

Although we know of no other measurement

system superior to our own, our capability

is, in part, inadequate, and we are attempting to improve it. In reporting the capability of the National Measurement System, I have not dwelt on .the actual performance in terms of ^^(f). A description in terms of ^^(t) is usually

adequate. There are cases, however, when a Sy(f) description is at least he lpful and

"perfiaps indispensible. One such case is for

primary standard research and development.

The measurement of S (f) both increases the

The Division's activities should also be

examined from the viewpoint of the Supplier/

Users matrix of section 2.5. In row 6, with

NBS as the supplier, the reader will observe

some letters. They are the output categories

listed in this section and in Section 2.5.1.1).

In those cases where more than one letter

appears, the first represents the output upon

which the two descriptors were evaluated.

(See sec 2.5.1.2.1.) When two or more are

given, the additional letter(s) represent

outputs which are too significant not to mention. . , . . ,

I have, for convenience, again listed some

of the areas in which the Division is involved.

The sections in which the discussions appear

are given parentheti cally.

- Custody of national standards (2.2.2

2.3, 4.1)

- The international measurement system

(2.4.1)

- Relationship to other central standards

authorities (2.4.1)

- State and local offices of weights and measures (2.4.2)

- Regulatory agencies (2.4.2, 2.4.4)

- Relationship to lower echelon calibration laboratories and services (2.4.3,

2.5.2.1)
- Role in the dissemination and enforcement network (2.4, 2.5, 4.1

)

- Support of science, education, and the

dissemination of knowledge (2.2.5,

3.1 .1

)

4.2.2 Users of NBS Services

The users of the NBS standard T&F broadcasts are numerically our most important

clientele. Moreover, as shown in sections

4.1, 4.2.1, and 4.2.3, the broadcasts are strongly tied to the primary standards and

the time scale. Thus, the services of the

primary standard and the time scale are made

widely available. This section will be con- fined to the users of stations WWV, WWVH, and

to the NBS telephone time-of-day service.^

Of the three NBS broadcast stations—WWV,

WWVH, and WWVB— station WWV has, by far, the

most users with such widely varied applications that it is nearly impossible to obtain

a comprehensive understanding of them. Never- theless, the_ Division has completed an attempt

to do just this, with a side benefit of an increase of the overall perspective of the

National Measurement System for T&F. In this section I attempt to summarize the

results of the questionnaire sent to survey

the users of the radio station services.

The questionnaire is reproduced as appendix

A. 3., and complete results and discussion

given in reference 42.)

Beginning on January 20, 1975, a questionnaire was sent out to obtain information

about the users of WWV and WWVH. It attempts

to determine who uses these stations, which

of the several services they use, and for what

appl ications they use them. Twelve thousand

questionnaires were completed and returned.

At the present time both WWV and WWVH transmit eight categories of information:

- Time of Day: Voice

- Time of Day: BCD Code

- One second ticks

The stations WWV and WWVH perform another

service which is not directly related to T&F but which is, nonetheless, quite important. The signals broadcast at each frequency leave the transmitters at' a fixed

power level. Thus, a monitoring of the

broadcasts versus time gives a person a good measure of the propagation conditions

over this path and for these frequencies.

It. is the great reliability of our broadcast operations that allows this function

to be served.

- Standard Frequency*

- DUT 1 values (DUT 1 is the difference

between a mean solar time known as UTl and an atomic time containing "leap"

second adjustments which is known as UTC)

- Weather

- Geoalerts

- Propagation Forecasts

The questionnaire asks about degree of use and degree of importance for each of these

categories. (For the category of standard

frequency, it asks the same for each of the

carrier frequencies.) The user is asked to identify both his organizational affiliation

and his principle application for the T&F service. Among the other questions asked is the degree of adequacy of the accuracy of the

service.

Degree of use, importance, and accuracy

were each to be judged in one of four possible

qualitative categories. For degree of use^ the categories are frequently, sometimes,

rarely, never. For degree of importance

the categories are: very important, somewhat

important, relatively unimportant, very un- important. For accuracy they are: more than

adequate, adequate, marginal, useless. The

results are displayed in tables 5, 6, and 7. Table 5 quantifies the relationship between

the eight broadcast services and the 14 organizational affiliations with respect to the

degree of use of the service. The procedure

for quantification is to assign the value, 0, to each "never" response, the value, 1, to each "rarely", 2 to "sometimes", and 3 to "frequently."^ These values are then summed

for each of the eight services and for each

of the 14 affiliations - 112 possibilities

in all. The sums for each affiliation are

then divided by the total number of respondents having that affiliation. The result,,

necessarily, is a number lying between 0 and

3. These values appear in the individual

elements of the matrix.

It. is also desirable to have an overall

view of the use of each service. This was obtained for each service by adding all the

values for that service and dividing by the

In "Standard Frequency" I include the

carrier frequencies themselves and the audio

frequencies of 440, 500, 600, and 1000 Hz (1200 Hz at WWVH). The carrier frequencies

are 2.5, 5. 10, 15, 20, and 25 MHz. 'The reader should very carefully note the

non-linearity of this scale. A linear scale

would be more desirable but who knows how to quantify qualitative judgment?

41
42
total number of respondents. These results

are listed in parentheses following the ser- vice in the left column. Also appearing in

the matrix, beside the column labels, are the total number of respondents for each

affiliation.

Summarizing the "relative use" data: as

a whole, the three most-used services are voice announcements of time-of-day, one second "ticks", and standard frequencies. Of

those, voice TOD is by far the most used.

Those affiliations whose use deviates significantly from the average are also apparent.

Looking at the distribution of respondents

as a function of affiliation, the result

seems consistent with other things we know

about the National Measurement System for

Time and Frequency. The category of "other"

is very large, probably because it contains

a great many amateur radio operators. Other

information has indicated that there are hundreds of thousands of amateurs.

This same procedure was followed in terms of relative importance . The results were so close to those of relative use (table 5) that

I have not displayed them. Using this same quantifica^oTi scliTe (0 to 3), the question of adequacy of accuracy

was studied. (See table 6.) Probably the

most important single conclusion is that,

for the majority of users, the accuracy is at least adequate. It would be nice to know

about the adequacy of accuracy of each of the

eight services, but, to reduce the complexity

of the questionnaire, it was decided to simplify by generalizing about all the services.

The response to "flie use of the Tix carrier

frequencies shows that 5, 10, and 15 MHz are

by far the most used, with 10 MHz being the

most used of all.

The applications to which T&F are put

are shown in table 7. The respondents

generally checked more than one "principal

use'^so that the total is over 29,000.

The NBS telephone time-of-day service

was also investigated in the questionnaire.

This revealed that a significant number of

phone calls come from out of state, mostly

from the East Coast, but some even come from out of the country.

In the last quarter of 1970, certain T&F information was made available from the Fort Collins stations via telephone. By

dialing 303-499-7111, the user can hear

the WWV broadcasts.

IrTthe last quarter of 1970, certain T&F information was made available from the

Fort Collins stations via telephone. By

dialing 303-499-7111 the user can hear

the WWV broadcasts. Counters were installed

to tally the calls and records were kept of

the number received per week. The results

Table 6: Adequacy of WWV-VH services

to various users Other 2,,54

Communications 2.,49

University 2,.47

Shippi ng/Boating 2,,43

Gov't Mil. 2.,43

Avi ati on 2,,42

Seismology/Geophysics 2, Telephone 2,.40 Navigation 2,.40

Equip. Mfg. 2,.40

c . Pleasure Boating 2,.39

Stds. Labs 2,.31 Electric Power 2,.29

-Avg. 2.

Table 7: Distribution of respondents

by principal use

No. of people responding

Principal that a given use characUse terizes their use

7149

3995

3358

2793

2513

2468

1813

1810

1170

842

641 287

260

are shown in figure 8. Two things should be

noted about the figure: first, the growth

in use has been rapid and, apparently, is still continuing; and second, the absolute

number of calls is quite impressive, presently

running about 17,000 per week. We estimate

that the total number of calls for the whole

of 1975 will be about one million.

All in all, I think it can be said that

the NBS broadcasts and the telephone services

have a large audience and many of these users appear to use the services as part of other

important technologies.

Calibration of Watches/

Clocks

Amateur Radio Instrument Calibration

Propagation Forecasts Navigation/Position

Location

Storm Warnings

Hobby (other than amateur radio)

Communications Systems

Geoalerts

Astronomy

Scientific Data Monitoring

Rocket/Satellite Tracking

Other
„ i ' !

i

=

j

% of

0

'

1 —

:

i

1

1

i

i5?2 I 1073 I I

Figure 8: Calling rate for NBS Time-of Day service (303-499-7111)

(A subsidiary but important function of the

stations WWV - HWVH is their relationship

to measurement and prediction of radio pro- pagation conditions [ 45]).

4.2.3 Alternate Sources

The NBS time and frequency services have

been extensively djscussed in section 4.2.1.

For the" present purposes, it is useful to generalize a bit on what was said there. In considering alternatives I describe the

Division's activities in three major categories: first, broadcast of standard T&F,

essentially the same as "Signal" in section

4.2.1; second, stable and accurate sources

of T&F, roughly equal to "Source" of 4.2.1;

and t'.ird, research and development of

dissemination-reception means for T&F, com- bining "Receiver" and "Dissemination Means"

of that section. The terms "Publish" and

"Consult" are included in varying degrees in

each of the three.

The "listeners" to our broadcast services

clearly predominate numerically. For the

large majority, the quality of the sources

upon which our broadcasts are ultimately

based is not a major consideration. (See

sec. 4.2.2.) I will explain and then con- sider the need for a central agency which

develops and operates very accurate (as well

as stable) standards of T&F. The discussion

of these first two services will show the

need for research and development in dissemination-reception. The point is that there

is a need for a central agency which attempts

to oversee the entire spectrum of T&F technology. This point of view is the one from

which the subject of alternatives to NBS services is best considered.

4.2.3.1 Broadcasts

We should separately consider the standard

frequency and time interval services from

those of date. The broad utility of the frequency services provided by the NBS broadcasts have been adequately covered in sec- tions 4.2.2, 2.4 and 2.5. We should consider

however, whether some other organization

might not provide the same service on a more

economical basis. It would be possible to simplify the operation for the vast majority

of users of the frequency and time interval

parts of our broadcasts, and the simplification would make a small reduction in the cost of operation. For these users the

broadcasts could be based on three commercial

cesium standards such as is being done in the new AT&T system (see sec. 2.5.2.3). There

would be no need for reference to a primary

standard, and the accuracy of such a system

would be about 1 x 10'^^. For almost all users, the received accuracy and stability

would be as good as it is now. However, for

those who need frequency accuracy greater

than 1 X 10 " the control of the broadcasts

44
by a primary frequency standard is indispensible.

Standard time intervals of, for example,

a few seconds to a few years could also b^j

generated to an accuracy of about 1 x 10"

without a primary standard. Thus, over a whole year's time, the probable accumulated

time error would be a few hundred microseconds. On the other hand, a time scale

formed from a very sophisticated ensemble of

commercial cesium standards, and calibrated

by a primary standard, can keep time to a few microseconds over a year.

There are other countries with standard

T&F broadcast stations similar to WWV. Of

these, Canada and Great Britain radiate

signals which are of usable strength in

restricted portions of the U.S. The U.S. Navy operates several standard T&F broadcast

stations, one or more of which is nearly

always accessible anywhere in the U.S. However, the format of the Navy's broadcasts

and the nature of their broadcasting schedule

make them of significantly less general use

than those of WWV, WWVH, and WWVB. Date is based on the angular position of

the earth with respect to other celestial

bodies. It is atomic-time keepers who best

know how large the second is but it is astronomers who best know what the date is. By collaborating with some group that makes

the proper astronomical observations, an adequately stable electronically-based time

scale can be calibrated to yield date. The

BIH coordinates the astronomical measurements

of several laboratories to provide the best

estimate of date.

Because of the existence of commercial

cesium standards it would be possible to operate such a station without access to a primary standard. This means that a non-NBS

operated service would satisfy most users. The control of the broadcasts by a primary

standard is, however, worth its cost, which

I hope to make clear in the next section.

Assume for the moment that this true and

also, that NBS is the organization best

suited for developing and operating a primary

standard. The point to be considered then

is not whether somebody else should run the

broadcast services, but rather, can NBS run them at lower cost for the same or better

service? Division personnel believe that

the answer to this is yes, and I discuss

this further in sections 4.4 - 4.5.

4.2.3.2 Accurate Standards

The importance of accuracy centers on the

need for coordination. Sometimes it is coordination internal to an organization;

sometimes it is coordination between organizations or between functions. An example

of an internal need for coordination is the

frequency division multiplexing system of

AT&T. One major thing that their new atomic

reference (see sec. 2.5.2.3) provides is a signal whose frequency is highly invariant

with time. The reason is that accuracy

establishes a limit upon how far the frequency

is likely to drift in long-term.

An example of coordination between functions

is the recent improvement in the knowledge of

the speed of light [l6]. This measurement

rests on an enduring relationship between the

unit of frequency and the unit of length, so that accuracy is again needed.

Definitions of physical units in terms of

natural invariants such as the "clock transition" in cesium potentially allows closer

coordination between originally independent

systems. As a hypothetical example, consider

the possible cooperation between AT&T and

the position location industry. The AT&T

frequency equalization system is based on cesium standards as is some of the position

location industry. Because both systems

depend upon standards whose absolute frequency is highly invariant, there is a potential for an efficient calibration service.

The telephone system could serve to check

frequency equality between isolated standards

within the position location network.

In practice, the greater the accuracy of

individual oscillators, the less the amount

of communication needed to achieve and maintain a given level of frequency and time . coordination between them. The existence of

a primary standard - a standard whose absolute frequency is known much better than that

of commercial standards - serves as a check

upon the accuracy claims of commercial standards. A primary standard should have an accuracy which is at least an order of magnitude better than the accuracy of the devices

which it is checking. This not only increases

the believability of the results, but, because

its stability is also at least this good, the

difficulty of making the measurements is also

decreased.

This allows me to return to the subject of

controlling the broadcasts of a T&F station

with a primary standard. For those who are attempting to hold frequency equalization to the limits of the accuracy of commercial

cesium standards, reference to such a station

is an important cross check.

The level of accuracy and stability pos- sessed by some users is high enough that access to a primary standard is very important. For some, access via radio broadcast

is sufficient. For others, a calibration at the site of the primary standard itself may

be necessary. Is there any other organization

which could more economically develop, maintain, and - if necessary - improve the pri45
mary standard? I contend that no private

organization attempting to make a profit

would take on the task of the primary standard: the costs are too high and the potential market is too small because the value

of the primary standard tends to be in its

long-term effects upon T&F technology. Thus,

it is difficult to price the service high

enough to make a profit in short term. The

primary standard of frequency is a classic

example of what economists call a "collective

good". I have not excluded, of course, the

possibility that some other governmental or private, non-profit, organization might more economically do the job. In the absence of

evidence to the contrary, however, I contend

that the whole concept of primary standards

is most "at home" at NBS. It is difficult

to believe that some other organization could

do as good a job at a lower cost.

4.2.3.3 Dissemination-Reception Research

and Development

There are a multitude of applications for

T&F. The carrier frequencies and broadcast

format of the NBS stations tend to be optimum

for serving these applications, but some

users are not adequately served. It is an important part of the mission of this

Division to improve the means by which we

can serve the user or, by which he can serve

himself. Sometimes this effort takes the

direction of trying to improve access

(remote access) to the primary standard and

the time scale. At other times it is directed

to reducing the cost - in money and labor - the user must incur to get the same quality

of T&F. This service, therefore, becomes

inseparable from the two previously discussed

services. In fact, my point is that all three services comprise an entity that is best described as a "collective good".

I don't think that there is an alternative

supplier of the NBS services, although there

are some changes in our resource allocations

that could make us more cost effective. I will discuss this subject in sections 4.4

and 4.5.

4.2.4 Funding Sources for NBS Services

We receive most of our funding from

Congressional appropriations. A minor

amount of funding comes by transfer from

other government agencies or by reimbursements for calibrations and similar services.

4.2.5 Mechanism for Supplying Services

This subject is discussed in great detail

in sections 2.4, 2.5, 4.1, 4.2.1, 4.2.2, and

4.2.3.

46

4.3 Impact of NBS Services

4.3.1 Economic Impact of Major User Classes

and

4.3.2 Technological Impact of Services

These two subjects are discussed in section 3.1.

4.3.3 Pay-off From Changes in NBS Services

This subject is most believably considered

by studying past activities rather than spec- ulating about the future. Fortunately, we

are in a good position to look back. The

best two examples I can give of benefit from

changes in service are with respect to our broadcasts. In section 4.2.2 I discuss the

results of a current study of users of our broadcasts. The study shows that voice

announcements of time-of-day and one second

"ticks" are the two most highly used services

of our broadcast stations. The latter service

was added in 1937 and the former was added in 1950. Other additions to our broadcasts have

also been favorably received.

4.4 Evaluation of NBS Programs and

4. 5 The Future

The history of NBS time and frequency

programs is replete with many successes and some attempts in the "other-than-successful

category. The development and documentation

of NBS-4 and NBS-6 places these two devices

among the four best national standards in the

world. The expansion of frequency measurement

technology from the microwave to the visible

and the measurement of the velocity of light

have received continued high praise from

scientific groups and our advisory panel. The

development of widespread radio dissemination

and of the expansion of the types of services

has received high ratings from user groups

and made time and frequency the most accessible

of the fundamental standards. Because time and frequency are used in so many places by so many people, and for so many purposes, it is not possible to con- cisely describe their importance to society.

The study of the National Measurement System

for Time and Frequency has attempted to en- compass the broad spectrum of this technology

by examining the system from three vantage

points

1. ) f:he instrumentation which is the sourae of T&F

2. ) the interrelationship between

suppliers and users of T&F

3. ) several of the calibration hierarchies

which provide compatibility between

the many sources
Time and again, in each of these views,

the economic aspects of the system emerge,

along with the fact that the time and frequency services of the NBS are absolutely

essential to our technological society.

In order to provide these services at all,

there is a logical chain of activities ex- tending from the operation and development

of the base standard to the operation of an effective delivery system for T&F information

to the user community. Not only has the

National Measurement System for Time and

Frequency Study identified the present needs

for T&F, it has identified growing needs for

the future. Thus, the NBS programs must (and

do) include significant elements designed to meet the needs of the future as well.

In section 2.5.1.2.3, I considered the

likelihood of three major changes in the

National Measurement System for Time and

Frequency:

1. ) A widespread network of clocks, syn- chronized to about 1 to 10 y seconds.

2. ) A low-cost, easy-to-use, means of

obtaining frequency equalization in the range 1 x 10"^ to 1 x 10

3. ) A low-cost, very widely available

means of obtaining time-of-day to an accuracy of about 0.1 seconds.

The third area of probable change could

well force some modifications in the delivery

of time-of-day within the telephone system.

It might also require some additional re- sources on the part of NBS. The solution

to this problem is, however, well within the

present technology and will (if it arises)

be primarily an economic problem.

The current dissemination-reception work

in the Division is quite consistent with

the first two trends in the system. It appears that the current program to provide

standard T&F broadcasts via satellite would

go a long way toward accommodating the first

area of probable change. In addition to this,

it would provide a general replacement for

the present broadcast services at a much

lower average yearly cost. The present esti- mate is that the average yearly cost could be

reduced, in the period around 1980, from

about $1.5 X 10^ to about $4 x 10^ This

savings of about $1.1 x 10^ would be of

great importance in supporting other worthy

programs within the Division.

The second area of probable change is being

addressed by one current program and another

which will soon begin. The very important

results already obtained with the TV "color

burst" technique should be of great utility

here. [38] This work - like that on the

satellite broadcasts - is another good exarhple of being aware of and making use of a dissemination system, some of whose properties

are superior to those of our broadcast sta- tions. In addition to this continuing project, the Division is about to commence work

on a feasibility study for a low-cost,

medium-accuracy oscillator.

We have a coherent Division program which

both addresses current needs and is directed

towards the probable future:

1. ) The maintenance and operation of the

primary frequency standard and the

time scale.

2. ) The maintenance and operation of the

three broadcast stations.

3. ) Research and development on a possible

standard T&F broadcast service via

satel 1 ite.

4. ) Primary standard research and development.

5. ) Further development upon and encouragement of the use of the TV "color burst"

technique.

6. ) Feasibility studies for a low-cost,

medium-accuracy oscillator; the

"utility" standard.

7. ) Further testing, and possible encouragement of the use of, a technique for

evaluating two major systematic errors

in beam-type atomic frequency standards.

Automation of the broadcast stations.

A search for new methods for improving

T&F dissemination.

Areas 1 and 2 are our responsibility both

by law and by historical involvement. Pos- sibly the latter is an even more powerful

force for our continued efforts. In the case of a reduction in funds, these two areas should be the last to go. The satellite broadcast service, if implemented, would be doubly important; it would

significantly reduce the cost burden for an essential service, and also provide a time

synchronization service highly compatible

with the first area of probable change mentioned previously. This work should have

highest priority after our legal obligations.

Research into better primary standards is an essential investment in the future. Here,

the word "better" should include ease of use

as well as higher stability and accuracy.

We strongly feel , however, that no construction

plans should be made for a replacement for

the present standards (NBS-4 and NBS-5) for

at least two years. And, only then if actual

needs within the National Measurement System

show that the present standards are becoming

inadequate.

The TV technique and the utility standard

have two strong similarities. The market for

both will probably be important by 1980. Both

47
could probably be done by private industry.

We think, however, because of skills already

available within the Division and because of

economic considerations in private industry,

that these activities can be most effectively

implemented by NBS and should remain a part

of our program.

As a part of the evaluation of the present

primary standards, a new technique for

evaluating certain systematic errors in beamtype frequency standards was developed. It appears that, using this technique, commercial

cesium standards can - in effect - be made

accurate to better than 1 x

10"''^. This

technique should be further evaluated. If,

in fact, the method is proven to be generally

useful, then it should be made available to those who can use it. The position location

industry is a likely candidate. Areas 5, 6,

and 7 in the above list are all excellent

examples of the "collective good" nature of

our work.

Automation of the stations can, potentially,

save a lot of money in the next two to eight

year period. Nevertheless, we give this

(possible) activity lower priority than the

satellite work, because we believe that satellite broadcasts will prove considerably

superior to land-based broadcasts both in

overall cost and in quality. At the present time, there do not appear

to be other dissemination methods showing more promise than those now under study

either by NBS or by other groups. We would,

therefore, assign lowest priority to additional

work of this type.

The essential points being addressed above

are (1) that the process of providing effective time and frequency information must be

approached in a systematic and logically co- herent manner, and (2) the NBS programs are carefully designed with this in mind.

5. SUMMARY AND CONCLUSIONS

The National Measurement System Study

should have two types of effects: first, it

should indicate proper programmatic directions;

and, second, it should provide confidence

that these programmatic directions are proper

ones. This is quite analogous to a statistician's interest not only in the average value

of a quantity but also its spread or uncertainty.

Of course, it is logically possible that

the programmatic directions uncovered by the

study are already the directions being taken.

In point of fact, this is essentially the case for much of what is concluded and this

should be considered a healthy state of

affairs. This is true because the National

Measurement System Study formalizes and ex- pands a continuous and less formalized effort

implicit in much of what has been done for

years. Indeed, it would be quite surprising

(and even devastating!) if it were not so. Even though essential concurrence in pro- grammatic directions was found, some new thrusts were identified and (hopefully)

significantly greater credibility for the

entire program has been achieved.

Noteworthy in the new directions already

taken have been the increased broadcast

schedule for radio station WWVB, and our efforts to reduce the operating expenses at WWV/WWVH/WWVB. In the first instance, it was found that many users (especially electric

power companies and seismologists) need the WWVB signals in a reliable and uninterrupted

fashion, and as a result, equipment at WWVB

was provided to avoid the former routine,

off-the-ai r-mai ntenance period. In the

second instance, plans to reduce costs at the stations are being undertaken which involve a survey of the users, initiated as a part of the National Measurement System

Study. One aspect of this survey is expected

to reveal features of our services which can

be discontinued with a net cost saving. The

survey is scheduled for completion by July 1,

1975, and preliminary results are already

available.

Our efforts in satellite time dissemination

and on a TV frequency transfer system seem quite appropriate in light of the study. In general, the study gives strong evidence

that it would be totally inconceivable for

the U. S. not to have an internationally

coordinated, accurate, and readily available

time and frequency service like that provided

by the NBS.

A great many people in the Time and Fre- quency Division of the NBS have contributed

information to this report. Earlier studies,

similar in nature to this one, have been

particularly helpful

Several people have contributed directly

to this study: Mr. John T. Stanley did an extensive study of the T&F needs of the

aviation industry. Mrs. Sandra L. Howe was

the major contributor to the study of the

NCSL standards laboratories. Mr. Lawrence

E. Gatterer made important contributions to understanding the uses and users of time.

Dr. Yardley Beers made valuable editorial

suggestions.

Drs. Raymond C. Sangster-and James R. Seed,

as coordinators of the entire study of the

National Measurement System have increased

the scope of this particular report.

Dr. Sangster made helpful editorial suggestions . Mrs. Karen Merrell typed the report and

made valuable contributions to editing.

48
APPENDIX A.l GENERAL METHODOLOGY

Based on the experience of personnel in

the Time and Frequency Division, and an earlier

study performed by the Division entitled

"Study of Time and Frequency Dissemination",

eight areas were selected for further investigation. The eight areas examined were:

- Standards Laboratories

- Users of NBS Radio Broadcasts

- Telephone Industry and Specialized

Carriers

- Military

- Position Location

- Aviation Industry

- Electric Power Industry

- Shipping and Boating Industries

In the present work, the literature available depended upon the particular area under

study. For the Common Carrier work, the

four volume report entitled "World Telecommunications" by Arthur D. Little, Inc. was exceptionally useful. The trade magazine

"Telephony", and the Bell System publication,

"Bell Laboratories Record", were also quite

helpful. Each of these sources was also of some help in the study of the Military, primarily because military communications leans

so heavily upon the telephone industry.

In the Shipping and Boating and the Electric Power Industry investigations, there were two books that provided important information: The American Practical Navigator

by Nathaniel Bowditch, and Power System

Operation by Robert H. Miller.

In each of the above four areas, additional

information was obtained by personal contact. Most of these contacts were by telephone. In these areas, of the order of 100 people were

contacted - some of them several times.

In the other areas, other than the Standards Laboratories, telephone and face-toface contact was the primary means of information gathering. Initial contacts were

identified by Division personnel, with these sources leading to additional people. Approximately another 100 people were contacted

here.

The other major source of information was

via questionnaire. Appendices A. 3 and A.

were used in the studies of the users of NBS Broadcasts and the Standards Laboratories,

respectively.

A third major use of the questionnaire

method was for technology forecasting.

Appendix A. 2 reproduces the questionnaire

and other information sent to the participants. The various aspects of this questionnaire and its results are summarized in

section 3.2.

APPENDIX A.

This appendix contains a copy of the

questionnaire and explanatory material

which was sent to each of 107 potential

participants, figure 5 represents the

responses to the first set of questions.

Ideally, these 107 people represented the

entire set of all those people who are knowledgeable about the matters discussed.

If this were true, and if, all those 107 people had responded, then there would be

no question about the statistical validity

of figure 5. Although a strong attempt

was made to poll the entire qualified - and

none of the unqualified - population I have no acceptable measure of the degree to which I succeeded. Moreover, only about

50 people of those polled responded, and even then, only about half of the respondees

responded to any given question. Thus,

even for the most definitive items (such

as the period 1985 in item 7) a serious

question of statistical validity can be

raised.

Despite this drawback I believe it is a mistake to ignore this data. In the text

I explicitly discuss only items 1, 5, and

7 - those items which (for the period 1985)

give the most definitive results. In these

discussions I give other information, all of

which is consistent with the results of

figure 5. With these qualifications then,

nothing more can be usefully said and each

reader will reach his own conclusions about

the interpretation of figure 5.

49
THE ISMSYITUTE OF

V ELECTRICAL A!MO ELECTRONICS

* ENGINEERS, INC. TECHNOLOGY FORECAST & ASSESSMENT PROJECT

2029 K STREET N.W., WASHINGTON, D.C. 20006 SUITE 603 (202) 293-2120/785-5137

September y, 1974

uear Sir:

The Teciinology Forecast and Assessment Committee of the IEEE Communications

Society is engaged in attempting to develop forecasts of future communication needs. In fact, many IEEE Groups and Societies are engaged in technology forecasting and assessment under the overall direction of the

IEEE Technology Forecast and Assessment Project. The National Bureau of

Standards is engaged in a similar venture through its systematic study

of the National (ieasurement System. The IEEE Communications Society has,

therefore, agreed to participate vnth the NDS in the Time and Frequency

(T&F) portion of this study.

We would like to encourage your participation in a Delphi study of the

future needs for time and frequency technology. Delphi is a technology

forecasting technique based on the polling of a panel of experts and is explained in more detail in the Foreword which accompanies the questionnaire.

The IEEE Communications Society's TF&A Subcommittee is participating in

this study because of its general relationship to technology forecasting

and because of its very direct bearing upon communications.

If you decide to participate in this study, please return the completed

questionnaire to Ur. Allan S. Risley in the preaddressed, prepaid

envelope. Further details are given in the Foreword.

Thank you very much for your cooperation.

Very truly yours,

William Ilorsch Manager, TF&A Project

WM/ar

Enclosures

50
September 9, 1974

Dear

This is an invitation to participate in a study that attempts

to forecast the future of Time and Frequency Technology. If you

agree to participate, it will require answering a questionnaire

now and again in about two months. On the second occasion, you

will be supplied with a summary of the results of the first

polling. In light of this summary, you might (or might not)

choose to modify some of your original answers. This general

procedure has become known as the Delphi technique of technology

forecasting.

WHY SHOULD YOU WANT TO PARTICIPATE? Answering the questionnaire will take a fair amount of effort, but these questions bear

on a technology that will importantly influence your career. A

good response from all participants will give you a chance to

observe the opinions of a wide spectrum of your colleagues.

The Time and Frequency (T&F) Division of the National Bureau

of Standards (NBS) is one of many divisions engaged in technology

forecasting and assessment. The major goal of our study is to

develop a socioeconomic basis for determining the research,

development, and services in T&F that the NBS should perform.

A Delphi study is needed because there are so many sectors

of society experiencing such a wide variety of pressures that no one person or small group can do this forecasting. By doing this

study, we hope to sum up the effects of those many sectors and

all those many forces that ultimately result in a changed T&F

technology.

There are three questions. The first asks about the

probability of use of eight different T&F Resources. Any

one of these Resources is a technological possibility; that

is, it may be feasible to build and therefore, it could be a potential resource to society. The eight Resources fall into two

groups: The first four refer to individual oscillators. The

second four refer to disseminated quantities. These "Resources"

are good approximations of what is likely to be the desired T&F

technology of the future

.

The first question uses the phrase "will be in significant

use." This is defined on the page entitled "DEFINITIONS AND

RESOURCES." In the list of Resources, the terms "frequency

repeatability" and "frequency equalization" are used. These,

also, are defined.

Notice that I stress use. It is one thing to prove technical

feasibility for a change in technology and quite another to secure

its implementation such that it becomes a part of the working

economy. The first question is based on the assumption that

each of the Resources will be feasible (in all senses

quality, cost, and field utility) sometime between now and the

year 2000. Your task is to decide the likelihood that a given

51
Resource will be "in significant use" on any of the given dates.

Of course, you may decide that a given Resource will not be

avialable (that it is not feasible) on any of the given dates,

in which case you should mark "Virtually Impossible" for that

Resource on that date. All prices are based on 1974 dollars . We have gone to some pains to try to pick qualified participants. In a real sense, there is no one qualified to predict

the future. On the other hand, you may have some measurable

effect in creating that future with regard to your own sector.

I therefore ask you to be prudent but imaginative; cautious

but not timid. If you truly feel inadequate to answer a given

question, then the "Not Qualified" blank should be checked.

The second question asks about the pressures that each

of the seven sectors (see question 2 for the sectors) will

exert to try to insure that a given Resource is available by

19 80. The pressures could take many forms. For example, the

Navigation Industry might encourage the Oscillator Manufacturers

to engage in a research and development project with regard to one or more of the Resources. You should attem.pt to answer this

question for your sector only. If, of course, you feel competent

to answer for one or more of the other sectors, please do.

The third and final question deals with those technologies

which have had great importance to one or more of the seven

sectors. This question attempts to determine what the future

importance of these technologies will be in each of the sectors.

Answer for other sectors only if you feel qualified.

The responses will be processed both as a whole and by sectors.

The data will be given in such a way that tendencies toward con- sensus or diversity will be apparent. I have about 15 participants

for each of the seven sectors. Although they will be identified

by sector, they will not be identifiable as individuals. I feel

that sector identification is important in order to detect a possible difference of views between sectors.

If you decide to participate, please return the completed

questionnaire in the preaddressed, prepaid envelope. If you

can complete the questionnaire within two weeks, it will be

greatly appreciated. If you decide not to participate, please

check the box for that purpose on the front of the questionnaire

and immediately return the questionnaire via the prepaid envelope.

I thank you in advance for your cooperation.

Sincerely yours.

Allan S. Risley, Physicist

Time & Frequency Division

National Bureau of Standards

Enclosure

52
QUESTIONNAIRE ON TIME AND FREQUENCY TECHNOLOGY:

FORWARD

If, after having read this Forward and having examined the

questions, you decide not to participate, please check this

box and return this material via the prepaid envelope.

[ ] Thank you for the opportunity to

participate in this study, but I have decided not to accept.

If you know someone else qualified to participate, check the

box below and return only this page to us in the prepaid

envelope.

[ ] I cannot participate in this study.

However, I have forwarded the

questionnaire to

who is highly qualified to answer

these questions.
DEFINITIONS AND RFSQilRCFS

DEFINITIONS

1. ".... will be in significant use .":

This means that the Resource has been applied to such an extent that it has

become an important part of normal operations. It would be disruptive to do without it.

2.. "Frequency repeatability....":

In discussing frequency repeatability, I refer to any two devices of the same model from the same manufacturer that may be initially calibrated against a reference or each other. Under these conditions, and for frequency measurement

averaging time of 1 second or more for Resource #1; 10 3 seconds or more for Resource #2; and 1 day or more for Resource #3; the frequency difference between

the two devices shall not exceed the values stated for at least one year of service. This is a "one sigma" statement.

3. "Frequency equalization....":

Refers to the ability to set the frequency of an oscillator located at a field

site equal to the disseminated frequency to within the specified tolerance. This

is also a "one sigma" specification and applies to the specified averaging time.

4. "Time synchronization....":

The ability to make a specific pulse of a local time scale occur simultaneously

with a specific pulse of the disseminated time scale. That is, to cause the local scale to be "on time" with respect to the disseminated scale. It is to be understood in this definition that propagation delays are accurately compensated

5. "Field utility. . . ." : Refers to the sensitivity of the device to such things as temperature change,

vibration and shock.

RESOURCES (All prices are based on 197^ dollars,)

1. Frequency repeatability of 1 x lO"^'' with improved field utility for $1K per unit.

-12

2. Frequency repeatability of 1 x 10 with improved field utility for $5K per unit.

-14

3. Frequency repeatability of 1 x 10 with limited field utility for $15K per unit.

-9

4. Frequency drift per day of 1 x 10 with high field utility for $100 per unit.

5. Frequency equalization to 1 x 10~^^, for 15 minutes of averaging, for $200 per station.

-14

6. Frequency equalization to 3 x 10 , for 10 days of averaging, for $10K per station.

7. Time synchronization to 2 microseconds (one sigma) for one minute of signal recovery

time, for $200 per station, anywhere in the U. S.

8. Time synchronization to 30 nanoseconds (one sigma), for 10 minutes of signal recovery

time, for $10K per station, anywhere in the U. S.

54
1. GIVE THE PROBABILITY FOR THE YEARS 1980, 1985, AND 2000, THAT EACH OF THE FOLLOWING TSF RESOURCES WILL

BE IN SIGNIFICANT USE. ALL PRICES ARE BASED ON 1974 DOLLARS.

RESOURCE Ouali- Virtually Relatively Relatively Virtually

fied Impossible Unlikely Likely Certain

1. Frequency repeatability of 1980

1 X

10"^'' (one Sigma) with 1985 improved field utility for

$1K per unit. 2000 ; ; ; ; ; ; ;

2. Frequency repeatability of 1980

-12

1 X 10 (one sigma) with 1985 improved field utility for for $5K per unit. 2000 :; ;; ;; ;;

3. Frequency repeatability of 1980

-14

1 X 10 (one sigma) with 1985 limited field utility for ?15K per unit. 2000 ; ; ; ; ; ; ;

4. Frequency drift per day of 1980

-9 not more than 1 x 10 with iqri; high field utility for SlOO per unit. 2000 ; ; ; ; ; ; ;

5. Frequency equalization to 1980

1 X 10 ''(one sigma), for 15 1985 minutes of averaging time, for $200 per station. 2000 ; ; ; ; ; ; ;

6. Frequency equalization to 1980

-14

1 X 10 (one sigma) , for 1985 10 days of averaging, for

$10 K per station. 2000

7. Time synchronization to 2 1980 microseconds (one sigma)

,

for one minute of signal 1985 recovery time, for $200 per

station, anywhere in the U.S. 2000

8. Time synchronization to 30 1980

ns (one sigma) , for 10 minutes of signal recovery time, 1985

for $10K per station, anywhere

in the U. S. 2000

55
0) '0 Rl C7t U O B V O S W Z

0) -O (0 CT M O E 0) O £ to Z U £ n Z

0) 'O (0 M O g 0) U £ ui Z u S to z

0) rd O tn M O B V u s n z

u s: m z

(0 (II rH

0) t3 Id Of O E W Z U S ui Z U £ U Z

113 0) <H rH M O B « o £ ta z U £ to Z O £ » Z

U E W Z O E W Z U £ CO Z

0) D a« ^ O S Q) O £ W Z O £ tn z O £ CO Z O £ W Z U £ Ul Z

<U 10 CP

»4 O B 0) O E 0) Z

V Tl (d Di M O E 0) O £ W Z O £ ui Z

Id <U iH ^

n 0 e « U E cn z W E W Z U £ Ul Z

4J h r^ -H

Id (U r-l H

a> Id cn u o B v U E tn Z O £ (n Z

y r-t -H

Id 0) ^

0) 'O Id C7> 1^ O B 0) O E W 2

4J M rH -H

Id <U M <H

0) TJ Id M O B 0) O E W Z

Id 0) rH H

(1) 13 (d tT> U O B 01 O E « Z

01 (d Di M O B 01 U E » Z4) (0 tP M O B 0) U E ui Z U £ M Z

0) 'O rd M O B 0) O £ CO Z

Id 01 ^ rH

0) T3 Id D> U £ 01 Z

01 TJ Id CP U O B 9t O £ to Z

0) TJ Id tn M O B 0) O £ CO Z u S to z U E to Z U £ to Z U £ CO Z

Id fl) H ^

U S CO Z U £ to Z

P V< M -H

Id o ^ iH

o> -o (d tji 1^ O B 0) U E CO Z

01 Id CP U O B 01

t:) £ to z U E to Z

ffi 0) •-> -H U £ CO Z

0) Tl Id U £ to Z U £ to Z

Pi o 'c

56
01 rH (U rH 01 rH 01 rH 01 rH 01 rH 01 rH H CP rH CP rH CP rH CP rH CP rH CP rH M to M 10 Sh to to M (0 u 10 U 10

10 " e — 10 " E r^ to r-, E " as r-. E r^ to r. e 10 r-. E" 10 ^

>J 10 O] ij 03 1^ 03 iJ ^

03 hi 03 h^ 03

1 —

1 — 1 ^ 1 •-• 1 •—

'0 tJl CP T3 tP 01 CP TJ CP 0 0 (U 0 01 0 01 0 01 0 01 0 01 s z s z 2 Z E z s z E 2 a z

0) rH (U rH OJ rH 01 rH 01 rH 01 rH 01 rH

CP 1-1 CP H t7> rH CP rH cn rH 01 rH 01 rH

10 u 10 M to U to U 10 u 10 u 10 6 " 10 r-. e 10 E ^ (0 r^ E r^ to r^ E — lO r. E r- 10 r^ E riJ J ^

tJ 03 I-] 03 03 03 1-1 03

1 " 1 " 1 —

1 " 1 " 1 —

T3 tJl •a CP X) CP T3 CJl "0 01 T) 01 •d 01 Q 0 Q) 0 01 0 01 o 01 0 01 0 01 s z a z s z E z E z a z a 2

0) Q) rH 0) rH 01 rH 01 rH 01 rH 01 rH en iH CP rH cn rH CP rH CP rH CP rH CP rH M to U lO to M to to u to to 10 ^ 10 — e " to r. E r- to .-. E r- to r^ E r^ to r^ E " 10 r-. E r1-1 03 03 1-1 03 03 03 rl 03

1 " 1 — 1 ^ 1 1 '—1 1 1—

1 "

o CP 'O CP a CP T3 CP T) 01 a CP -d CP 0 0 OJ 0 01 0 01 0 01 0 01 0 01 s z z E Z E z s z E 2 a 2

(U i-H (1) rH 01 rH 01 rH 01 rH 01 rH 01 rH

Cn rH CP rH Cn rH CP rH CP rH CP rH CP rH M (0 rl U to u to u 10 IH to u 10

(0 --H e (0 r-, e r^ to r-, E r- to — E r^ to r^ E r^ 10 ^ e r- 10 r^ E "

ij 03 03 1-1 03 03 03 iJ 03

1 " 1 --' 1 " 1 •—

1 •—1 •—1 — 1 " 1 •—

•a Cr 0 CP TD CP T3 CP CP TD CP •a CP 0 01 0 Mo

01 0 01 0 01 0 01 0 01 s z z z E z s z E 2 s z

(V rH (U rH 0) rH 01 rH 01 rH 01 rH 01 rH

Di rH CP rH ffl rH CP rH CP rH CP rH CP rH U (d u rO u to k to to u to VI to

(8 10 — e r- to —

.

E " to E r- 10 r- E r- 10 " E r- ID r^ E —

03 03 I-) 03 iJ 03 ij 03 hi 03 hj ^

03

I " 1 •—

1 >—1 " 1 — 1 >-• 1 — 1 " 1 ^

T) cn a CP •a CP a tji 01 CP T3 CP 0 0 (U 0 01 0 01 0 01 0 01 0 01 s z z s z s 2 E 2 a z a 2

ID 01 rH (1) rH o; rH 01 rH 01 rH 01 rH

t7< rH CP rH CP rH CP rH 01 rH CP rH Di rH U m u to IH to u to u to to VI 10

rO ^ e " (0 — 5 " 10 r^ E — to r- E r^ 10 E — to r-, E r^ 10 r-, E "

J 01 J to 1-1 03 iJ 03 03 rl 03 iJ 03

1 — 1 " 1 ^ 1 ^ 1 " 1 ^ 1 "

o CP TI CP a Di -a CP a CP a CP TD CP 0 <u 0 OJ o 01 0 01 o 01 0 01 O 01 E z s 2 a z E z E 2 a z

0) rH 0) rH 01 rH 01 rH 01 rH 01 rH 01 rH

rH CP rH CP rH CP rH 01 rH CP rH CP rH

(fl u to u to u to M 10 u to Vl 10 10 — e r^ ta r^ E r^ 10 " E r- to r^ E r- to r^ E r- 10 " E — to r-, E —

1-q ^0) CO 03 03 03 ij 03 iJ 03

1 " 1 " 1 " 1 " 1 •— 1 — 1 "

T3 0> a CP -d CP T3 CP T3 CP n Di T3 CP 0 <u 0 01 o 01 0 01 Mo

01 0 01 0 01 s z s z s z E z Z s 2 a z

2 z 33 u u M M Eh z z cu M X

M M < 03 O 03 03 s <

x; X u u X < U Q < Q

u z w z w Z 2 z H 2 u — 03 w ~- U 1 o O O M u o 03 O 2 O M 2 fci W M 04 M Q. M X ij H >i M W M Oi Z bl H O

D (/J M 03 M 03 O u Eh X H Eh O 03 Eh 03 1-] 1 a H t^ ME M Eh H Eh H < 0< 2 < O U

E OS

bl U

w > J > tj > H X u o 63 U U PS W CO a

« M O H 3 M H S M o w 5 O S w 0< H W LA TI Q s Eh Q S EH Q 03 > J W ij 03 tH 0<

03zO Eh H 2

03

U O* U

H H <

2 D fci 3 O 3

a U Z

O S

_U

03

OS u o S

Eh O

hj <

H lu U D

03 2

O <

o

I M

Z EH o <c

1-1 Eh

Eh DS < O

a a, H 03 > S

Eh

032

O 2 "

M 03 < W

Eh W K Z

< U Eh O

U H S

M > « O, Z OS W W

3 W X J

a 03 Eh W

E O Eh O —

u

SNOiivonddv

57
APPENDIX A.

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Bouldar, Colorado 80302

January 8, 1975

Dear Participant:

In response to government-wide efforts to reduce operating costs and con- serve energy, we are considering various alternatives for operating radio

stations V/WV and WWVH. Interested listeners to these stations are being

asked to provide information, via the enclosed questionnaire, which will

help us set priorities and guide our decision-making processes with

respect to these services. Examples of possible changes include the elimination of some broadcast frequencies from WWV and/or WWVH or reductions

in transmitted power on some frequencies.

As a result of greatly increased energy costs at our Hawaiian radio

station, WWVH, we have already solicited comments from users regarding a proposed 50 percent reduction of power at 5, 10, and 15 MHz from WWVH

only. We have received so many objections to this proposal that we have

decided to explore other possible means of cost and energy reductions. It

is hoped that the responses to this questionnaire will allow us to provide

the services needed most within our financial constraints and at an efficient level of energy use. Thus, it is very desirable that you provide us with thoughtful responses to the enclosed questions. Please fold the

questionnaire in thirds with the return address on the outside and staple

or tape it closed and mail. No postage is necessary if mailed within the

U. S. However, a postage stamp is necessary if a reproduced copy of this

questionnaire is mailed.

Your help is greatly appreciated.

Sincerely,

Enclosure

58
CM

a

0) i/l > t o ^

u. ^Q.

Q. • < O EU 00 o z

LiO

CD

CO

ITa

lU o > 0. J z

UJ < > ^- " a H O < a J I a z

UJ (r z o

0. in z < Ui r (-

I- <D

Ul

aa z < > u. o< (r a a D S u o u z < <

q: a.

tu o > 0.

UJ (r z o o a.

Ifl z

IT) •-« ^ UJ

D 3 U 21 I I U. Z UJ Z tu •- (T 3 U. < O Ol I I X LLl cr UJ u. ^

q: I- UJ I I

il

D

g

59
ZQ£08 opejojoj 'japjnog

uo/s/A/g AoudnbdJj pue 3iu/_i

/' spjepueis P neojng iBUOiisf^

DOES "sn B5»*Mcl ">( *>|OU»d

8S3NISna IVOIddO

?oeo8 cnvaonoD uaainoa pjDpuBis |o nBSjng |buo|30(\|

33H3IMM03 iniaiMxuvdaa s n

aiVd S33j QNV aSViSOd

60
APPENDIX A.

4

1. Do you provide frequency calibrations for your ovm organization?

2. Do you provide fvequency calibrations for groups outside your organization

3. Do you provide time interval calibrations for your own organization?

4. Do you provide time interval calibrations for groups outside your

organization?

5. Approximately how many time and/or frequency calibrations do you provide

in-house customers over a years period?

6. Approximately how many time and/or frequency calibrations do you provide

"outside" customers?

7. What are your customers' uses and projected area of needs for frequency

and time calibrations?

(1) communications and related equipment?

(2) navigation?

(3) power line control and regulation?

(4) geophysical time and frequency needs?

(5) precision test equipment for other application?

(6) other — Can you give details?

8. What is a good estimate of your yearly operational cost of the

frequency and/or time portion of your service?

(1) $100 - $1000

(2) $1000 - $10,000

(3) over $10,000

(4) over $50,000

9. What is a good estimate of the capital investment in your frequency

and time calibration equipment?

10. What frequency and time standards do you maintain in your lab?

11. Do you use NBS frequency and time services? (Booklets [SP-236 Time Scale]

relative to these services are enclosed.)

12. Of the frequency calibrations you perform, in which accuracy class

do most fall?

(1) more accurate than a part per million

(2) less accurate than a part per million

(3) other (specify)

13. Do you foresee time and frequency calibration services increasing in

your organization?

14. Can you discuss future applications for time and frequency calibrations

in your organization?

USCOMM-NBS-DC

61
References

[I] Jespersen, J. and Fitz-Randolph, J., NBS Time and Frequency Handbook, Title and

publication details not yet available.

[2] Hellwig, H. W., Atomic frequency standards: a survey, Proc. IEEE, Vol. 63, No. 2,

212-229 (February 1975).

[3] Kamas, 6., editor, NBS Time and Frequency Handbook. Title and publication details

not yet available.

[4J Blair, B. E., editor, Time and frequency: theory and fundamentals, Nat. Bur. Stand.

(U.S.) Monogr. 140 (June 1974).

[5J' ibid. , Chapter 5

L6] ibid, Chapter 8

[7J Barnes, J. A., et. al . , Characterization of frequency stability, IEEE Trans, on

Inst, and Meas., IB-20, No. 2, 105-120 (May 1974).

[8] Blair, B. E.,' editor, Time and frequency: theory and fundamentals, Nat. Bur. Stand.

(U.S.) Monogr. 140, Chapter 10 (June 1974).

L9] ibid. Chapter 6

[10] ibid. Chapter 11

[II] Howe, S. L., and Risley, A. S., ihe NBS study of the time and frequency needs of U.S.

standards laboratories, NCSL Newsletter, Vol. 15, No. 1 (April 1975).

[12] Risley, A. S., The time and frequency needs of the U. S. telephone industry: A

portion of the study of the National Measurement System, An Internal NBS report

dated May, 1974.

[13] Hellwig, H. W. , A review of precision oscillators, NBS Tech. Note 662 (January 1975).

[14] Risley, A. S., A study of the shipping and boating industries as a part of the

study of the National Measurement System, An Internal NBS report dated July 26, 1973.

[15] Blair, B. E. editor. Time and frequency: theory and fundamentals, Nat. Bur. Stand.

(U.S.) Monogr. 140, Chapter 7 (June 1974).

[16] Evenson, K. M., Wells, J. S., Petersen, F. R., Danielson,' B. L., and Hall, J. L.,

Speed of light from direct frequency and wavelength measurments of the methane-stabilized laser, Phys. Rev. Letters, Vol. 29, No. 19 (6 November 1972).

[17] Jennings, D. A., Petersen, F. K., and Evenson, K. M., Extension of absolute frequency

measurements to 148 THz; frequencies of the 2.0 and 3.5 ym Xe laser, to be published.

62
[18] Field, B. F., Finnegan, T. F., and Toots, J., Volt maintenance at NBS via 2 ^/^: A

new definition of the NBS volt, Metrologia 9, 155-166 (1973).

[19] Kamper, K. A, and Zimmerman, J. E., Noise thermometry with the Josephson effect,

J. Appl. Phys. 42, No. 1, 132-136 (January 1971).

L20J Delattes, R. D., et. al.. Determination of the Avogadro Constant, Phys. Rev. Lett.

Vol. 33, 463.(1974).

[21] Thomas, J. B., and Fliegel, H. F., lime and frequency requirements for radio interferometric earth physics, Proc. 5th PTTI Conference, 15-31, Washington, D.C. (1973J

[22] Hafele, J. C, Keating, R. E., Around-the-world atomic clocks: predicted relativistic time gains. Science 177, 166-167 (July 14, 1972).

[23] Pound, R. V., and Rebka, G. A., Jr., Apparent weight of photons, Phys. Rev. Lett.,

337-341 (April 2, 1960).

[24 J Kleppner, D., Vessot, R. F. C, Ramsey, N. F., An orbiting clock experiment to

determine the gravitational red shift, Astrophys. and Space Sci. 6, 13-32 (1970).

[25] U. S. Industrial Outlook 1973, a U. S. Department of Commerce Publication.

[26] World Telecommunications, Vol. 3, 75 (copyright by Arthur D. Little, Inc. 1971).

L27J Stanley, John T., Time and frequency applications in the aviation industry, to be

published as an NBS internal report.

[28] Statistical Abstract of the United States, 1972.

[29] A personal communication with an official of the U. S. Maritime Administration.

L30J Poulson, B. W. , and Kranick, R., Some aspects of the economics of the U. S.

communications industry, an internal NBS report.

[31] Risley, A. S., A historical view of the relationship between technology and other

features of society, to be published as an NBS Technical Note.

[32] Risley, A. S., I he creation of a Delphi study for forecasting time and frequency

technology, Proc. of the 1974 National Telecommunications Conf. San Diego, Calif.

(December 2-4, 1974).

[33] Perkinson, R. E., and Watson, F. D., Airborne collision avoidance and other applications of time/frequency, Proc. IEEE, 572-579 (May 1972).

[34] American Telephone and Telegraph Company Digital Data System. Compatibility and

interface specification at the inter-digital serving area DS-1 level, (July 1973).

63
[35J Snyder, W. F., Achievement in radio: seventy years of radio science and measurement

at the National Bureau of Standards, to be published as an NBS Special Publication

in 1977.

L36J Blair, B. t., editor, Time and frequency: theory and fundamentals, Nat. Bur. Stand.

(U.S.) Monogr. 143, Chapters 4 and 5 (June 1974).

[37] ibid. Chapter 3.

[38] Davis, D. D., Calibrating crystal oscillators with tv color-reference signals.

Electronics, 107-112 (March 20, 1975).

[39J Risley, A. S., Shoaf, J. H., and Ashley, J. R., Frequency stabilization of x-band

sources for use in frequency synthesis into the infrared, IEEE trans, on I & M,

Vol. IM-23, No. 3 (September 1974).

[40] McDonald, D. G., et al . , Four-hundredth-order harmonic mixing of microwave and

infrared laser radiation using a Josephson junction and a maser", Appl : Phys. Lett.

Vol. 20, 296-299 (April 1972).

[41 J Walls, F. L., and DeMarchi , A., RF Spectrum of a signal after frequency multiplication; measurement and comparison with a simple calculation. Submitted to IEEE

Trans, on Instr. and Meas.

[42] Barnes, J. A., and Beehler, R. E., Report on the 1975 survey of the services of

radio station WWV and WWVH, NBS Technical Note 674 (October 1975).

[43] Allan, David W., "The Measurement of Frequency and Frequency Stability of Precision

Oscillators," NBS Technical Note #669 (May 1975).

[44] Howe, David A., "Frequency Domain Stability Measurements, a tutorial introduction,"

NBS Technical Note #679.

[45] Tilton, Edward P., "The DXer's Crystal Ball," QST, June 1975, Vol LIX No. 6,

August 1975, Vol. LIX No. 8, and September 1975, Vol. LIX No. 9.

I

i

64

I
NBS-114A (REV. 7-73)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBS SP-445-12. Gov't Accession

No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

The National Measurement System for Time and Frequency

(Study of the National Measurement System,

NBS Special Publication # 445-I

5. Publication Date June 1976

6. Performing Organization Code

7. AUTHOR(S)

Allan S. Risley

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No. 2770900

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Same as Item 9.

13. Type of Report & Period Covered Final

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

Library of Congress Catalog Card Number: 76-608114

16. ABSTRACT (A 200-word or less factual summary of most sigriificant information. ' If document includes a significant bibliography or literature survey, mention it here.) The results of a study of the National Measurement System for Time and

Frequency are given. The system is viewed from three vantage points:

1) The Instrumentation that provides sources of time and frequency (T&F).

2) The Suppliers and Users of T&F. 3) The Calibration hierarchies for T&F

sources. An attempt is made to determine the technological, scientific,

economic, and social effects of the system. Predictions are made about

possible important changes in the system. The past, present, and possible

future position of NBS in the system is described in detail.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name: separated by semicolons) i^tom\c frequency Standards; Aviation industry; Electric power

industry; National measurement system. Position location; Shipping & boating industries;

Standards laboratories; Telephone industry & specialized carriers; Time & frequency;

Time scales; Users of NBS radio broadcasts.

18. AVAILABILITY [X Unlimited

I

' For Official Di stribution. Do Not Release to NTIS

I Order From Sup. of Doc, U.S. Government PtiatingjQffi-ce Washington, D.C. 20402, SD Cat. No. C13 • l":^^5-i

I ! Order From National Technical Information Service (NTIS)

Springfield, Virginia 22151

19. SECURITY CLASS

(THIS REPORT)

UNCL ASSIFIED

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

21. NO. OF PAGES

72

22. Pr

$1.20

USCOMM-Oq 29042=

*U.S. GOVERNMENT PRINTING OFFICE: 1976 210-801/287 1-3







NBS TECHNICAL PUBLICATIONS

PERIODICALS JOURNAL OF RESEARCH reports National Bureau

of Standards research and development in physics,

mathematics, and chemistry. It is published in two sections, available separately:

• Physics and Chemistry (Section A)

Papers of interest primarily to scientists working in these fields. This section covers a broad range of physical and chemical research, with major emphasis on

standards of physical measurement, fundamental constants, and properties of matter. Issued six times a

year. Annual subscription: Domestic, $17.00; Foreign,

$21.25.

• Mathematical Sciences (Section B)

Studies and compilations designed mainly for the mathematician and theoretical physicist. Topics in mathematical statistics, theory of experiment design, numerical analysis, theoretical physics and chemistry, logical

design and programming of computers and computer

systems. Short numerical tables. Issued quarterly. Annual subscription: Domestic, $9.00; Foreign, $11.25. DIMENSIONS/NBS (formerly Technical News Bulletin) —This monthly magazine is published to inform

scientists, engineers, businessmen, industry, teachers,

students, and consumers of the latest advances in science and technology, with primary emphasis on the work at NBS. The magazine highlights and reviews such

issues as energy research, fire protection, building tech- nology, metric conversion, pollution abatement, health and safety, and consumer product performance. In addition, it reports the results of Bureau programs in measurement standards and techniques, properties of matter and materials, engineering standards and services, instrumentation, and automatic data processing.

Annual subscription: Domestic, $9.46; Foreign, $11.85.

NONPERIODICALS Monographs—Major contributions to the technical liter- ature on various subjects related to the Bureau's scientific and technical activities. Handbooks—Recommended codes of engineering and

industrial practice (including safety codes) developed

in cooperation with interested industries, professional

organizations, and regulatory bodies.

Special Publications—Include proceedings of conferences sponsored by NBS, NBS annual reports, and other

special publications appropriate to this grouping such

as wall charts, pocket cards, and bibliographies.

Applied Mathematics Series—Mathematical tables, manuals, and studies of special interest to physicists,

engineers, chemists, biologists, mathematicians, comput'er programmers, and others engaged in scientific and technical work.

National Standard Reference Data Series—Provides

quantitative data on the physical and chemical properties of materials, compiled from the world's literature and critically evaluated. Developed under a world-wide

program coordinated by NBS. Program under authority

of National Standard Data Act (Public Law 90-396). NOTE: At present the principal publication outlet for these data is the Journal of Physical and Chemical

Reference Data (JPCRD) published quarterly for NBS

by the American Chemical Society (A(3S) and the American Institute of Physics (AIP). Subscriptions, reprints, and supplements available from ACS, 1155 Sixteenth

St. N. W., Wash. D. C. 20056.

Building Science Series—Disseminates technical infor- mation developed at the Bureau on building materials,

components, systems, and whole structures. The series presents research results, test methods, and performance criteria related to the structural and environmental functions and the durability and safety characteristics of building elements and systems.

Technical Notes—Studies or reports which are complete

in themselves but restrictive in their treatment of a

subject. Analogous to monographs but not so comprehensive in scope or definitive in treatment of the subject area. Often serve as a vehicle for final reports of work performed at NBS under the sponsorship of other' government agencies.

Voluntary Product Standards—Developed under pro- cedures published by the Department of Commerce in Part 10, Title 15, of the Code of Federal Regulations.

The purpose of the standards is to establish nationally

recognized requirements for products, and to provide

all concerned interests with a basis for common understanding of the characteristics of the products. NBS

administers this program as a supplement to the activities of the private sector standardizing organizations. Federal Information Processing Standards Publications (FIPS PUBS)—Publications in this series collectively constitute the Federal Information Processing Standards Register. Register serves as the official source of information in the Federal Government regarding stand- ards issued by NBS pursuant to the Federal Property and Administrative Services Act of 1949 as amended,

Public Law 89-306 (79 Stat. 1127), and as implemented

by Executive Order 11717 (38 FR 12315, dated May 11, 1973) and Part 6 of Title 15 CFR (Code of Federal

Regulations).

Consumer Information Series—Practical information, based on NBS research and experience, covering areas

of interest to the consumer. Easily understandable language and illustrations provide useful background

knowledge for shopping in today's technological

marketplace.

NBS Interagency Reports (NBSIR)—A special series of interim or final reports on work performed by NBS for

outside sponsors (both government and non-government). In general, initial distribution is handled by the sponsor; public distribution is by the National Technical Information Service (Springfield, Va. 22161) in paper copy or microfiche form.

Order NBS publications (except NBSIR's and Biblio- graphic Subscription Services) from: Superintendent of Documents, Government Printing Office, Washingrton,

D.C. 20402. BIBLIOGRAPHIC SUBSCRIPTION SERVICES

The following current-awareness and literature-survey

bibliographies are issued periodically by the Bureau:

Cryogenic Data Center Current Awareness Service A literature survey issued biweekly. Annual subscription: Domestic, $20.00; foreign, $25.00.

Liquefied Natural Gas. A literature survey issued quarterly. Annual subscription: $20.00. Superconducting Devices and Materials. A literature

survey issued quarterly. Annual subscription : $20.00.

Send subscription orders and remittances for the preceding bibliographic services to National Bureau of Standards, Cryogenic Data Center (275.02)

Boulder, Colorado 80302. Electromagnetic Metrology Current Awareness Service Issued monthly. Annual subscription: $24.00. Send

subscription order and remittance to Electromagnetics

Division, National Bureau of Standards, Boulder,

Colo. 80302.
U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Washington. D C. 20234

OFFICIAL BUSINESS

Penalty for Private Use. $300

POSTAGE AND FEES PAID

U.S. DEPARTMENT OF COMMERCE COM-21S

SPECIAL FOURTH-CLASS RATE BOOK

YEARS NBS 1901 - 1376