PB 151394

jioulder laboratories

^0.35

SERVICE AREA OF AN

AIRBORNE TELEVISION STATION

BY M.T. DECKER

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

motions and Aclivities

The functions of the National Bureau of Standards are set forth in the Act of Congress, March

3, 1901, as amended by Congress in Public Law 619, 1950. These include the development and

maintenance of the national standards of measurement and the provision of means and methods for making measurements consistent with these standards; the determination of physical constants and

properties of materials; the development of methods and instruments for testing materials, devices,

and structures; advisory services to government agencies on scientific and technical problems; in- vention and development of devices to serve special needs of the Government; and the development

of standard practices, codes, and specifications. The work includes basic and applied research,

development, engineering, instrumentation, testing, evaluation, calibration services, and various

consultation and information services. Research projects are also performed for other government

agencies when the work relates to and supplements the basic program of the Bureau or when the Bureau's unique competence is required. The scope of activities is suggested by the listing of

divisions and sections on the inside of the back cover.

Publications

The results of the Bureau's work take the form of either actual equipment and devices or published papers. These papers appear either in the Bureau's own series of publications or in the journals

of professional and scientific societies. The Bureau itself publishes three periodicals available from

the Government Printing Office: The Journal of Research, published in four separate sections,

presents complete scientific and technical papers; the Technical News Bulletin presents summary

and preliminary reports on work in progress; and Basic Radio Propagation Predictions provides

data for determining the best frequencies to use for radio communications throughout the world.

There are also five series of nonperiodical publications: Monographs, Applied Mathematics Series,

Handbooks, Miscellaneous Publications, and Technical Notes. Information on the Bureau's publications can be found in NBS Circular 460, Publications of the

National Bureau of Standards ($1.25) and its Supplement ($1.50), available from the Superintendent

of Documents, Government Printing Office, Washington 25, D.C.
NATIONAL BUREAU OF STANDARDS

technical ^Ttete

35

October, 1959

Service Area of an Airborne Television Station

by

M. T. Decker

NBS Technical Notes are designed to supplement the Bureau's regular publications program. They provide a means for making available scientific data that are of transient or limited interest. Technical Notes may be

listed or referred to in the open literature. They are for sale by the Office of Technical Services, U. S. Department of Commerce, Washington 25, D. C.

DISTRIBUTED BY

UNITED STATES DEPARTMENT OF COMMERCE

OFFICE OF TECHNICAL SERVICES

WASHINGTON 25, D. C.

Price $ .75
The studies contained in this report were

sponsored by the Ford Foundation's Fund

for the Advancement of Education.
ABSTRACT

As a step in the evaluation of a proposed airborne television

network, the service to be expected from an airborne station

has been calculated for a wide variety of operating conditions,,

The use of basic transmission loss to describe the radio

propagation effects enables the results to be used when equipment parameters are changed as system requirements and

economic considerations dictate.

SERVICE AREA OF AN AIRBORNE

TELEVISION STATION

by

M. T. Decker

INTRODUCTION

In order to assist in the evaluation of a proposed airborne

educational television network, the National Bureau of Standards has

undertaken a study to determine the coverage to be expected from such

stations, and an analysis of station and channel requirements for a

nation-wide system. The purpose of this paper is to show the service

to be expected from a single airborne station under a wide variety of

operating conditions.

It is the aim of the report to present various calculations in a

flexible manner such that the system designer may change at will any

of the factors which he controls and then determine the resulting effect

on the system. For this reason the "radio propagation factors" which

are controlled by nature, not man, are separated from the "hardware

factors" which, within limits, may be changed as system requirements

and economic considerations dictate. A natural choice of parameters

on this basis is the commonly used "basic transmission loss" [ 1] . Briefly, the basic transmission loss is the ratio of power supplied to

the terminals of a loss -free isotropic transmitting antenna to the power

available at the terminals of a loss -free isotropic receiving antenna,

expressed in decibels. The basic propagation information is this basic

transmission loss as a function of the geometry of the propagation path,

including effects of antenna heights, distance between antennas, the
-2-

atmosphere. and the earth itself. The characteristics of the actual

equipment, including transmitter and receiver performance, antenna

gains, various losses, etc. , will then limit the basic transmission loss

which may be tolerated by the system, still maintaining satisfactory

operation. This "maximum allowable basic transmission loss", together with the above described basic transmission loss as a function

of geometry, will determine the coverage to be expected.

Of course, most of the radio propagation factors and some of the

equipment characteristics are not invariant with time and/ or location.

Hence certain variabilities will be introduced along with a definition of

grade of service and the probability of receiving such a grade of service.

BASIC TRANSMISSION LOSS

Figures 1 to 19 show the calculated basic transmission loss L as

a function of distance for various combinations of transmitting and receiving antenna heights and for frequencies of 575 Mc and 785 Mc. For

these calculations the earth was assumed to be a smooth sphere having

-14

ground constants of <r (conductivity) = 5x10 (emu) and € (relative

dielectric constant) =15. A horizontally homogeneous atmosphere with

an exponential vertical gradient of refractive index was used to account

for the bending of radio rays [2] . This model is felt to be more closely

representative of the actual atmosphere than the linear gradient often

used and accounted for by the "4/3 earth" concept.

A curve showing the long-term median of basic transmission loss

was first calculated in three parts. This curve is labeled "50%" in the

figures. The surface value of refractive index used in the model atmosphere was 316.2908, as derived from data taken throughout the United
-3-

States *. The portion of the curve lying within line of sight was calculated by simple ray theory [3], and the characteristic lobe structure is

evident. Beyond the line of sight the diffracted energy was calculated

by the method developed by Norton, Rice and Vogler [4], and combined

with the energy due to atmospheric scattering as calculated by Rice,

Longley and Norton [5] . These three portions of the curve were then

smoothly connected to form the median basic transmission loss curve.

In order to include the effect of long-term time variability, i.e. the

variability of hourly medians, the additional curves labeled 1%, 10%,

90%, and 99% were included. The within line -of- sight curves were

calculated by using different values of refractive index at the earth's

surface in the model atmosphere. The values chosen represent the values which are exceeded 1% and 99% of the time respectively in the United

States. This method is similar to the practice of allowing for varying

degrees of radio ray bending by the use of different effective earth radii,

but, of course, allows the use of the improved atmospheric model. The

long-term time variability for the beyond line -of- sight fields has been

taken from the empirically derived curves of reference 5 which indicate

the difference between median fields and fields for other percentages of

the time, as a function of the angular distance, the angle between horizon

rays from transmitter and receiver. These curves have also been

* The choice of a surface refractive index of 316.2908 and the less

accurate but simpler assumption of a linear gradient of refractive index

result, for an assumed 6370 kilometer actual radius, in an effective

earth*s radius of 9000 kilometers. Under these conditions the line of

sight distance d from an antenna h meters above a smooth earth may be

found from d = 3 \T2 h where d is in kilometers and h is in meters.
-4-

modified to be a function of frequency.

The curves are presented for three transmitting and three receiving antenna heights and for two frequencies in the UHF television band.

Figures 1 through 10 are calculated for 575 Mc, the center of the lower

half of the UHF-TV band, while figures 11 through 19 are at 785 Mc,

the center of the upper half of the band. All of the figures with the

exception of figure 4 are calculated for horizontal polarization. Figures

3 and 4 may be compared to indicate the difference to be expected between the two polarizations over a smooth earth. The decrease in

magnitude of the reflection coefficient for vertical polarization as the

grazing angle increases results in nulls which are not as deep as are

those for horizontal polarization. Use of vertical polarization could be

advantageous for this reason. In addition, the alternate use of vertical

and horizontal polarization for geographically adjacent cochannel stations

would result in an improvement in the rejection of the interfering station.

It should be noted that the variation of basic transmission loss with

time at one distance is not necessarily correlated with the transmission

loss at any other distance, hence the entire curve need not shift at one

time as could be inferred from the plot.

SERVICE

The term "service" as used in this study may be defined as follows:

In the absence of interfering signals, service exists at a receiving

location during any hour for which the hourly median signal received

from the transmitting station exceeds the receiver noise power by

a specified ratio. In the presence of interference, this service exists

when the signal from the desired station exceeds the sum of the

noise power and interfering signal power by a specified ratio.

The term "grade of service" requires that service shall exist
-5-

for more than some specified percentage of all hourly medians. This

percentage as used in this study is taken to be 99% and will be referred

to as "99% grade of service".

VARIABILITY OF TRANSMISSION LOSS

Variations of the basic transmission loss from the computed median

have been divided into three categories. The first, the long-term variation of hourly median basic transmission loss has been included in the L

versus distance curves. Second, there are variations with time which

occur within the hour. These short-term time variations may arise from

various sources, including the irregularity of the aircraft antenna pattern

which combines with the aircraft motion to produce varying fields at the

receiver. Reflections of small magnitude from irregular terrain or

other objects, the effect of inhomogeneities in the atmosphere, which

may change with aircraft motion may also introduce short-term fading.

These short-term effects have been allowed for in this study by an increase in the required long-term median signal-to-noise ratio which is

required for satisfactory operation. An examination of many aircraft

antenna patterns (including the 1948 Westinghouse-Martin B-29 antenna

used for Stratovision flight tests) indicates that an allowance of approximately 10 db should be made for a 99% grade of service. The third

source of variability arises from the fact that the earth is not a smooth

sphere, but has many irregularities. This means that some locations

will be better for receiving signals than others, or put another way, not

all locations at a given distance may receive satisfactory service. In

order to allow for this variation it was assumed that service as determined by long- and short-term time variations alone could be expected
-6-

at 50% of the locations at any distance and that the probability of service

with respect to location could be represented by a log-normal distribution

with a standard deviation of 6 db [6] .

MAXIMUM ALLOWABLE BASIC TRANSMISSION LOSS

Equipment parameters are used to determine the amount of

transmitter power which may be lost between transmitter output terminals

and receiver input terminals and still maintain satisfactory operation of

the receiving set. The following factors should be considered:

Transmitter power, db above 1 watt P

Transmitter line losses, db L

t

Transmitting antenna gain, db above an

isotropic radiator G

Receiving antenna gain, db above an

isotropic radiator G

Receiver line losses, db L

r Required signal power at receiver,

db above 1 watt P

r The transmitter power and the signal power at the receiver should

have comparable specifications in the case of modulated signals such as

television. That is, if the transmitter power is referred to the peak of

the synchronizing pulse, receiver power should be specified in the same

manner.

The required signal power at the receiver may be determined from

the receiver bandwidth, noise figure, and required signal-to-noise ratio.

The required signal-to-noise ratio must include a consideration of the

required steady signal to produce a picture satisfactory to viewers, plus

an allowance for short-term time variations as indicated above. Various
-7-

studies of required signal-to-noise ratios have been made [7, 8] . Curves

published by the Television Allocations Study Organization (TASO) indicate

that 50% of the viewers rate a picture passable or better if the signal-tonoise ratio is 27 db. Similar studies by the National Bureau of Standards

indicated that a 26 db ratio would be satisfactory. The TASO study indicated that a ratio of 38 db is required before 95% of the viewers rated a

picture passable or better. The lower figure is used as an example but

the system designer may consider other values. An allowance of 10 db

for short-term fading has been included in the examples of maximum

allowable transmission loss presented here.

The required receiver signal power expressed in dbw may now be

determined from

P = 10 log, ktb + F + R

r 5

10

-23

where k = Boltzman's constant (1.38 x 10 )

t = absolute temperature in degrees K, here taken to be

288.48°, so that 10 log kt = -204 dbw/ cycle

b = effective bandwidth in cycles per second, approximated

here by the 3 db bandwidth

F = receiver noise figure in db

R = required signal-to-noise ratio in db.

Finally then, the maximum allowable basic transmission loss Ll , . may be expressed

L, ,. = P -L + G + G - L - 10 log,„ b - F - R 4- 204

b(max) t t t r r

to 10

As an example of this calculation, consider current commercial UHF

receiver performance characteristics as reported in reference 7 (Table

III, p. 121), and a 1 kw transmitter.
-8-

P 1 kw

L

t G

t G equivalent to a 1.5 meter

parabolic antenna

L 30 meters of RG8/ U coaxial

transmission line with fittings

10 log b based on "average" equipment

bandwidth of 20 Mc.

F based on "average" equipment

R based on signal-to-noise ratio of

27 db and 10 db for short-term

fading 37 db

30 dbw

2 db

4 db

18 db

8 db

73 db

13 db

Then

b(max)

= 30-2 + 4 + 18 - 8 - 73 - 13 - 37 + 204 = 123 db

A brief examination of the L, versus distance curves indicates that this

b

equipment performance would be completely unsatisfactory if reliable

service is to be maintained to any reasonable distance.

Consider next the improvement to be gained by the use of equipment built to more exacting standards. The receiver bandwidth is decreased to 6 Mc, the noise figure to 10 db, antenna gains increased, and

line losses reduced by the use of better transmission line. The terms in

the L , . equation then become: b(max)

P = 30 L = 3 r \ - l 10 log b =- 67.8

G = 5

t F = 10

G = 20

r R = 37

then L . . = 30 - 1 + 5 + 20 - 3 - 67. 8 - 10 - 37 + 204 = 140. 2 db o(max)
-9-

Further improvement inL, . . could be made in a number of wavs b(max) ' depending on the technical and economic limitations. The power transmitted from the aircraft could be increased, better antennas used, or

receivers with lower noise figures might be employed if service is not

limited by interfering signals or man-made noise at the receiving

location.

DIVERSITY RECEIVING ANTENNAS

An examination of figures 1 to 19 indicates that for certain transmitter-to-receiver distances the use of vertically spaced diversity

receiving antennas would be advantageous in reducing the signal fading

which may result from ground reflections as the aircraft moves. Experimental evidence indicates that these nulls as shown in the figures

may be present, especially where lower receiving antennas (10 meters)

facing a smooth unobstructed foreground are used.

The calculated lobe diagrams are based on a perfectly smooth

earth, resulting in high reflection coefficients, a condition not always

met over actual terrain at these frequencies. Hence, it would be expected that only the nulls at the greatest ranges (lowest grazing angles)

would be very deep. Thus, depending upon the maximum allowable basic

transmission loss, and antenna height, the nulls at shorter distances

would not affect the service.

A space diversity system as envisioned for this application would

consist of two antennas separated vertically on a single tower. Maxima

and minima of signal strength exist along this tower and their locations

are, in general, a function of frequency and terrain, and the range over

which aircraft height and distance from the aircraft to the receiver are

expected to vary. The heights of the receiving antennas are chosen such

that one of them will always be near a maximum. Suitable electronic

selection techniques would allow the stronger of the signals from these

antennas to be used for the television picture.
-10-

Approximate calculation of the heights of the maxima and minima,

and hence the proper location of the antennas, is simple for propagation

over a smooth earth. This type of calculation gives a rough idea of the

location of nulls and maxima, but in actual installations the locations may

be so modified by terrain irregularities as to require measurement of

signal strength as a function of height above ground for known aircraft

locations.

If either the transmitting or receiving antenna height is low and the

distance between them is large compared to their heights (as is the case

in the present study) the following approximate relation may be used to

find the height of a maximum or minimum over a smooth earth with

effective radius of 9000 kilometers and in a linear gradient atmosphere:

[9]

4500 n\d

h = —

r 2

18h - d

t where h = height of maximum or minimum at the low antenna,

meters

h = high antenna height, meters

d = distance between antennas, kilometers

\ - wave length, meters

n = 1, 2, 3, 4, • • • and is odd for a maximum and even for

a minimum

A correction may be applied to this calculation to allow for

radio ray refraction by an exponential refractive index gradient instead

of by the linear gradient atmosphere. Since there is less total bending

in the exponential atmosphere, a ray leaving the earth at a given initial

angle above the horizon will reach a given altitude at a lesser distance

than will a ray in a linear atmosphere. The above results may be

approximately corrected for this effect in the following manner. The

distance at which the heights of maxima and minima are desired is first

selected. This is the distance in the exponential gradient atmosphere.

The distance to be used in the above formula is somewhat greater than
-11-

this and may be found by the use of figure 20, adding the appropriate Ad

to the original distance chosen. The resulting height, h , is then applicable to the distance in the exponential atmosphere. Successive values

of n are used to find the maxima and minima heights at this distance.

Three examples of this calculation are given in figures 21, 22, and

23. These approximate locations of maxima and minima agree quite

closely with those shown in figures 1 to 19 which were done with a more

exact method by a digital computer. Figures 21 and 22 show the effect

of a change in frequency with the aircraft at one altitude, while figures 22

and 23 show a change in altitude at a fixed frequency. The heights of the

receiving antennas should be chosen such that one of them will always be

near a maximum, considering expected changes in both distance and

altitude.

COVERAGE

A single circle drawn on the surface of the earth does not adequately describe the coverage of a television station. It is better described by

an indication of the percent of locations receiving a given grade of service

at any given distance. For this reason no radius of coverage has been

mentioned in this report, but an indication of the overall coverage performance of a system may be gained from figures 24 and 25. It was

assumed that by the use of suitable antenna locations with space diversity

arrangements where necessary, and with maximum receiving antenna

heights of 30 meters, the basic transmission loss could be maintained

for 99% of all hours above the value found by combining a line which has

3 db less loss than the free -space transmission loss with the 99% curve

near the horizon. This assumption is considered applicable to 50% of the

locations at any' distance . For a given to L, . . and the previously menb(max)

tioned location variability the percent of locations receiving the 99% grade

of service may be determined. This has been done and the results plotted

for a range of L, , , values from 135 to 150 db, and for various trans

° b(max)

mitting antenna heights. The improvement to be gained from increasing
-12-

either the maximum allowable basic transmission loss or the aircraft

altitude may be readily seen in these figures.

Illustrations of the relative number of locations which could be

served by an airborne station are shown in figures 26, 27, and 28. If service were obtained everywhere throughout an area, the number of

locations which could receive service at any distance would be proportional to the circumference (or radius) of a circle at this distance. In the

present case, however, the probability of receiving service decreases

with increasing distance from the transmitter, so that at some point the

relative number of locations receiving service decreases in spite of the

larger radius. In the figures the relative number of locations receiving

service at a given distance is proportional to the height of the curve, and

the total number of receiving locations is proportional to the area under

the curve. It was assumed that the aircraft was circling at a fixed altitude with a radius of 15 kilometers, and that the location probability

applicable to a given increment of area is that which would apply with the

aircraft at the far side of the circle.

The following tabulation lists the effective areas under the curves

of figures 26, 27, and 28. This effective area is defined as the summation of incremental areas multiplied by the probability of receiving

service in each of these areas.

Frequency Aircraft Altitude

b(max) Effective Area

575 Mc 7500 m 140 db 30 5,000 km2

145 352,000

150 379,000

785 Mc 7500 m 140 db 271,000 km2

145 335,000

150 372,000

78 5 Mc 5000 m 140 db 191,000 km2

145 226,000

150 246,000
-13-

CONCLUSIONS

An examination of the basic transmission loss curves together

with calculations of the maximum allowable transmission loss indicates

that the system will require the use of carefully designed equipment

with maximum possible transmitter power and lowest possible receiver

noise figures. Currently available "average" commercial UHF-TV receiving sets as listed in the TASO report are probably not adequate for

this system.

A useful and versatile description of coverage has been presented

in figures 24 and 25. They are applicable to a wide variety of system

conditions and the subsequent figures have been derived from them.

Other figures similar to figures 26, 27 and 28 may of course be easily

obtained from them.

In order to achieve the system performance indicated in this report it may be necessary to employ diversity receiving antennas at

certain distances. The requirement will depend on the range of variation expected in aircraft height and distance and on the unobstructed

effective heights available at the receiver. It is likely that measurements will be required to establish the need for a diversity system at

the various receiving locations.

It would be highly desirable to instrument the initial system for

careful measurement of transmission loss over an extended period of

time. A careful evaluation of the usefulness of diversity receiving

antennas should be made.

Further theoretical work will be carried out to estimate the number of aircraft and portion of frequency spectrum required for efficient

coverage of the entire United States.
-14-

ACKNOWLEDGEMENTS

The author wishes to acknowledge the assistance of K. A. Norton

and P. L. Rice in the planning of this report and of the following persons

who aided in the various calculations: L.. E. Vogler, L.. G. Hause, G.

D. Gierhart, J. E. Farrow, D. E. Willwerth, R. P. Baptist, H. R.

Dahms, and M. J. Miles.
-15-

REFERENCES

[1] Kenneth A. Norton, "System loss in radio wave propagation, " NBS Journal of Research (D: Radio Propagation) 63D, 53-57,

July-August, 1959.

[2] B. R. Bean and G. D. Thayer, "Models of the atmospheric radio

refractive index, " Proc. IRE, 47, 5, 740-755, May, 1959.

[3] R. S. Kirby, J. W. Herbstreit and K. A. Norton, "Service range

for air-to-ground communications at frequencies above 50 Mc, " Proc. IRE, 40, 5, 525-536, May, 1952.

[4] K. A. Norton, P. L. Rice and L. E. Vogler, "The use of angular

distance in estimating transmission loss and fading range for propagation through a turbulent atmosphere over irregular terrain, " Proc.

IRE, 43, 10, 1488-1526, October, 1955.

[5] P. L. Rice, A. G. Longley and K. A. Norton, "Prediction of the

cumulative distribution with time of ground wave and tropospheric

wave transmission loss. Part I--The prediction formula, " NBS

Technical Note 15 (PB 151374) July, 1959.

[6] R. S. Kirby, "Measurement of service area for television broadcasting, " IRE Trans, on Broadcast Transmission Systems, BST-7,

23-30, February, 1957.

[7] "Engineering aspects of television allocations, " Report of the

Television Allocations Study Organization to the Federal Communications Commission, March 16, 1959.

[8] Kenneth A. Norton, Addendum to Reference "E" to the Federal Communications Commission Ad Hoc Committee for the Evaluation of the

Radio Propagation Factors Concerning the Television and Frequency

Modulation Broadcasting Services in the Frequency Range Between

50 and 250 Mc, November 16, 1950.

[9] Reference Data for Radio Engineers, International Telephone and

Telegraph Corporation, 4th Edition, 1956, p. 810.
CO

crUJH

_J UJ m ^ z: < o o

rr

~~* hIll <>

LJ2

h-X

UJ

N

rr<

(_> h- 1 o

-z. <

hco

crUJHI <

UJ

LL

_l< n h- z

fO ^ o

(O 2 <l

N >

co

O

_lto

Q

rroX

CO 2 O o £

rr _J o o

CO

(O

X

CO2

hrr<

CO

rr CO UJ UJ

-z.

X

H < UJ rr o .> o

r- o ^ "5 CJ o CO o

IO

inIs- CO rr h- lO < hi UJ > 1- >- o T o

(0 ^: 2O UJ

UJ3 <

cr> <n

X

\-u.< O

UJ

rr o rr

rr

u

Q_ tr

,,

II

///

//

o\/ o\° / 7

o/ o/

5*

crj 5—|

_jf_ _^ s^ .__ i i

io

Horizon '

Exceeded %

of

Timea / I

5?

IT) // 1 / / / .5 / / / / / / / /

// /

^J

UJo

COQ

aa 'sson noissinsnvhi oisvg
>

CO

CC

UJH

UJ m *£. ^

LUO2

<

cc<

>

UJ

crUJ

li

inX

S2

UJX

<

o

<

N

CC<

_l

o

0_

COn

UJ

_l

2

<o

<± o

CO z < M

>

CO CO

-z.

CCo

X

CO 2 O

o — (T _J sio

CO 2 X

en O

CO X

(O h-m CO ^ < rr CO UJ UJ 2

<

X

o

UJ en :> o

h- o > ^ CJ o (D u if) U) h- CO rr 1^ m

< in LD > 1- >- o T o

CO Z. ^ Ul o UJ 3 1 Of

h-<

(0 h- Ul

cc < u_ u.

Q. < O cc

CC O

Q_ cc

///

8

\y o\y

/ 7

sol \p ON / ON / o/ o/

N?

Oil

\

— —

j

x~~~>^^<- 1

"T= Nl ^

S £ |C^lr

.<o <3

>

jSm

5

/ —

s?

/ «

1

<o

/ /

/ /

/ /

/ /

1

/ .5

-J

1

/ /

/ /1

/

/

/

/

/

.5

to //

' -J

Ulo

-z. <

haa 'ssoi NoissiiAisNVdi oisva
CO

>- crUJ

_J

GO 2

-z. o < o K

tt ro < <> N

h-T LL UJ (0 <

Ill ^ UJ

_lo o H X QL

-z. "? < _l < rr tz <

h- hi p* h- co \- i-i i *± O I CO

h-2 UN

CO 2o < cro > _l

7?

X

CO CD -) CO ^ O O o

cr _l CO 2 X

en o

CO h- CO rr

CO <

UJ CO

cr P" X UJ <[ l- H

Q£ o LU 1- o ^ o o CO Oo LO CO<

cr

UJ

inIs- Is- m > 1— > o T o z CO

III o UJ ~)

\-

X o < UJ CO h- cr < u_ u. Q_ < o cr

CT

O

Q_ cr / / / /

05 / / / /

0) / / o / / -J / /

v„/ <>V

o\/ o\/

\°/

<3

y §1 o/ o O)

A <0/ C7)/ 0)/

cJy i / / ' Ql i /

05 /

,< 1 /~7s>^ZZ

— "I Zl i 1 sD

>> s J t

.N "fc S t Hi k o g o k Q

'5

q> ^ 5? $S

-° ig c; 0) <0 --

jja o> in

— o o> m 0:

S?o

in /

CJ / / / .5 / / / S / 'X 1 / / s^ / / !\ o

snoc / / / / 1/ 1

fc

.5

vj / / «« \ / // / /

v.

V / /

o> 1 / O // , s

—J / /

UJo

COQ

u.

aa'ssoi noissiiaisnvui oisvg
CO

>- cc

UlH

_l UJ 5 ^ z < o o

rr ro hUJo <>

UJ

1-X

S2

Ul <N

or<

.i H- X on Z<1-co UJ

I— <

-z. Ul

_i< Q 1 1—

i— e> z.

tr CO 2 <l

Lil > O

_lQ2 >

CO o ~» CO z o O

_l 8

cr 2 X

en

O

CO

X

CO lrr 2

CO <

UJ

to

Ul z x t- < >_ Ul or o 2 o K o ^ ^ o n CO (J lO

U) 1^- CO rr ^ m < UJ UJ > h- V o T o

(0 z

?» Ul o Ul r>

h-< X oUJ (0 h- ir < u. u. Q. < O rr

tr o UL or /

///

//s

en

// £ '

~~~A

-y^—y^7^^

—- T ^^ . ~] \\

***

^^^ oIf)

5? / / 1/ / / K ) 13 / / / / / / / '/ / / / / tf

Minima -

-J / / / / / /r /

Ulo

COQ

80 l ssoi noissiwsnvui oisva
co

>- tr

UJH _J UJ m ^ z <

tr3 o o<N

LUO

-z.

CO

UJ2 XO

UJ <

_J

tr

UJ

i—

X<

UJ o

CL

_l<

hQ T h- -z. o ^L o

co 2 < N >

CO o

_l oX

C/) 2 o 3 o

oro z X

CO o

CO

X

CO hir 2

CO <

UJ

to

tr

Ul 2 x I- < 1— UJ tr o :> o

h- o S > o o CO oo

in CO or o in < in OJ > 1- v o T o

CO z. o

UJ

UJ 5 X o

Ul CO 1- tr < u. u_

CL < O rr

tr

O CL tr

//

11

//

,W-o\°/-^ V O/ O / ° / & / ^

^1 \ j \-?^y^^

il f/7 ~~tt

adio

Horizo

ce

Exceede

9%

of

Time > Cu3 / /i o / C> 1 / / / / / / / / 1 1 /\5

~)

^j / / / / / / / / /

v.

// / -J

Ulo

COQ S

aa 'sson noissiwsnvui oisva
LUO

CO

COo

COz

<

CO

>- oc tp

- w z

j= LU O ^ X Q_

F. z <

CO i-

§ 1

CDo

X

CO

o

CO q; < LU CD >

O

<

CDO

cr

LU o

N

CCO

CO <

LUo

o

CO

CO

tr

LU

o

o

o

o

LUx

Li. <

cro

CC

in

ir> SE6

CD

LU

LU

CD

COQ

(X)

aa'ssoi noissiwsnvui oisva
co<o

CO<

00 >

CO

0T

m

«^ z. < O u

OC ro

55N

UJo

UJ

X

COUJX <

_lon <Hn

or

UJ

h- <

-z. Ul

h-

_i<

h-Z

CO < O

CO 2 N >

CO CO

Q

-z. 3 oX

CO 7"O 3 o

CO z CO o

CO

CO

X

h-rr

Ul

CO

ocui

h-ui

O ^ o

co

O

m

Q. hcc O in

uiO ^ o

-, I 5

ui o

Ul CO i- ¥- o < u. u. .5 Q- < V: o or cc o 1

o. oc V, __ O < <o

=3<JO\ o<

hcoQ

aa'sscn NoissiiAisiwai oisva
co >

crUJ

_J LU m ^ 2 < o O

cr< hh-<

UJ

X

S2

cr

LlJ o<

\-

(S) n > LlI . j

cri X<

UJ

h- o

CL

_l2

<n <d.

O

</) 2 <i

N > 3

CO

croX

U) 7*

O 3 O

a:CD

-z.

X o

tn

X

co

cr CO ^ < cr UJ en Ul 7? H <

cr

X

h-o

Ul o o o

CO ooo

CO cc lO

m < III ~~ m > h- >- o T o

CO ^

7*

— Ul o Ul X)

CD

X oUl

1- cr

<T u. u.

0. < O cr

cr o

Q. cr

///1

/)

N«\o/ °V °7 oN°/ 7 7 v // Oil \v ) > T

i*

Q

.q ki

.<0 ;

<5

U$>1 c / u

.6 111 / / // 1 111 1 / //

<5 .5

V1 / / / / // /

/// / /

^J

Ul

CJ

COQ

CO

aa 'ssoi NOissiwsNvai oisva
CO

>- rr

LU _1 LU m 2 2: < m

rr

—

H 3 H <N

in rr

LUO hLUX <

_in

IS

COn 5

a:

LlJ Hl <2

LU

1- <

h-2

CD 2

co 2 < M >

CO

Q2->

rrX

(/) z O o <:

rr _l <n o 2 X o

CO

X

<o h-

<r > < co

tr CO LU

LU z x t- < 1— LU rr o ^

i- o ^ > o o CO o

en rr

m 10 < hi m > I- V o T

(0 2 ^ LU o<

LUX 3O

LU

(0 \- ir < Ll_ u_ CL < O rr

rr o a. rr

LUO

COQ

aa 'ssoi noissiwsnvui oisva
CO

>-

UJ _l UJ m 2 z < o o

rr ro h- 2

UJ

X

CD <N

cr<

_i Ill S UJ o H X on

CO

ccUJ

I— <ZZ

UJ

_i< n 1 1— Z o z O

co z < N >

CO o

_l z oX

CO z o o o

rr _l o Zo

CO

X

CO

H

ir 2 < CO

a:

UJ CO LU 2 X

1—

\- < LU or o i> o

\- o ^ o CO oo

CO rr U)

m < hi OJ > I- >- u T o o z z UJ o UJ z>

HX o < UJ <0 h- ir < u. u_

LL < O rr

(T o

Q_ <r

//// 3 _ 8- / V

o\7 o\°/ o/ o/

<0/ CT)/

N?|

0)/

CD

—\~x~y

_ F\

'<?

Horizon

Exceeded

'o

of

Time-* = ' O Q = S8 ~ o

=—

—

Cu

_ o)5Cu31 — / S

.5 / / / / / / / / // 1§ / / / / / / / / /// / / us

of

Mini 

/ / / / / // / / / / / / oz<

Ico

aa 'sscn noissiiaisnvui oisva
LiJ O

-z. <

coQ

CO>

>-

DO<

cc<>

Ul

ccUJ

l-i oo

co

a:UJ

UJ


 <M X

UlX

LaJ Q

CO

CO3 io

CO

x

CO •"" — cc ^ < 00

cr CO iii Ul z x h- < 1— UJ cc o :> \- o

CJ CO CO cc < UJ CD >oo

cc

CL < N

CC

O

CCooO

m io oo H >-

C3 ^

UJX / / ////

/// / f1

^1

o\°/

W \o/ n?| --o 3\/ oW CiM 5/ O/ C / 0) / <o/ cr/ cr> \<l J _ _-^^^<Cl " 1

1/

—~y*~

^—

~~T t

7<^/o

Horizoi

:e

Exceedec

?%

of

Time

.to

O In 5 / ]S 1 Ii1 1 // AC3

•vi 1 / / / i / / / /

.5

<0 /// / / /

Ulo

-z. <

V-co

aa 'ssoi NoissiiAisNVdi oisva
LJ(J

CO

COCO

CO

en - w 2 E 12 5 § £E

ccUJ < _J

UJ

n 1 H

7" CO < > _l O

7* CO CD -1 CO ^ O

_l CD oN

CCOX

X

CO ~ X<

UJ CO

UJ

QC

O UJ \- ^

C_> 10

COOO

CO rr lO uu < UJ Is- f*- DQ >O X

>-

-z. CD

III UJ X)

1-

X < UJ

CD

H cc <CLO

ce

Q. <o

a:<

UJ

—

01 / 3 < o> \- ii. coQ

aa'ssoi noissiiaisnvui oisva
co

en

GQ<

CC<>

LU UJo

coQ

CO>

COcoQO

CO

CO

CO<

or oo

CO q; <t LU OQ >o<

CD<

CLo

q:

a.

IM

isUJ , — X

crUJI oooX

COX

hcr< 2 < o

cr

CO

LU

iLU

CD

(^

>-O

-z. LUo

LUcru_ / 1 II /1

K> / o\°/ o\C / o\7 \° ,°/ o/ s ! * <o/ CT>/ Oil

<j I §£ 1 /

<a

Ql it \ / _>

— ' I O O t 1

fc£

K

^"fc - 5? IS^i? Z " l > in <fc.g 0> If) .<0 Q b 5?m

5« -*

~i ' T~ 1 ' 1

r> / / / / // / / / <a / .5 / / * / / / 1 / / / / /

=5 / / /A<»

<0 / / ' p o\ / / / / / / /

.c$ \ / /

s^ \ / O 7 / $ / / <J / / o

-J / . ' / / / o<

coQ

9Q 'SS01 NOISSIIAISNVUl 0ISV9
UJo

coQ

CO>

COCO

CO

-z. <

orl-

>- c

_l UJ m 2 z

or<>

UJ <N

or<

_io

0_ ^ < UI I- z < o_J Q

CO o

CO3 § 5 £

or<

UJoo

CO

or

uiH

UI oN

oroX

O CO co cr <t UI CD >o5o

orCL oo id Q. oo o |<-

>-oz

UJo

UJ

or <

oro

or

II /

o\o/ o\y o\7 ae/s8

91 s./ 0/ o/ o/ 0> ^£ / "V *°/ °*,l ^ «

9> £

\l~\k.^y^-—

s"fc t fl

.3 "8 1

§? fc | « * S ^

<gO)*'

<:

y>Q

5*Oin

*so / /" 1 in / / 1 / / 1 .6 / / 1 | / / 1 3*V / / 1 / o / / L I / / \

^1 / / 1 .$ V / / / .c \)'/ / / ^* / / V> / / * / 3o

^J / / y

UIo

COQ

9Q

C SS01 NOISSIIAISNVdl 0ISV8
CO

_1 LU m ^ z

< ^ ° _ m —

cr<

>

lu S=!

e>

uj ^ o i- H a: CO lu

> 3

cocoS*

CO x

CO

CO<

IE

cr<

uj

o

o

o to CO q; < LU OQ >O

<

csotr

<

N

tr<

_i

o

0_

O

M

cro

Z>o

tr

CD

CO

trLU

I-LUO

"= o m

Q. co o I s- H >- T o

(0 *L

III LU -) X OLU K cr

Ll_ u_ <

tro

cr<

/

///

//

7f

J °7 °N / o/ O

7 °N

/ 0)\

Oil {

-\-y—y

I

>*

S5 5?1? c

Q S° 1

•S3 a *

*

in

> -*

' JT

> U•>

5

.5

' T

/

1

/ /

/

/

/

/

3

3

1

/ /

/ /

/ /

/ / 1

to .5

1

/ /

/ /

1 /

/

/

/

/

f 4 / ^1

LUO

COQ

aa 'ssoi noissii/vsnvui oisva
COCO

COz<

or

>-

Ico

acUl

lUI ^ o ^ rr rO H < 1- <

UJu

UJ2 Xo

Ul

or<

...i l- X on

enn

UlHI <zz

Ul

1-

-j<Z

CD z o

CO Z < N > U. r*> <r 3 5O<

UJoo

CO

ccUl

IUl oX o co g

CO q; < UJ CD >O<o

or

o. o r<-

>-oz

UloUl

oru <

oro

UJoz

COQ

8(3" 'SS01 NOISSII/MSNVUl 0ISV8
CO

COO<

h-o

CO<

CD

>- CO

cr

m<

q:

UJ ± O H H ^

CO £ Q I O

CO 2 > q

UJ < H N

11LU _| ^ O

Q_ <

UJ< N ^ a: o oX o

a:

Q

<"

CO

x ^ ^ to CO W Ul H * O ^ o^ ^ O

co o io O CO

cr io" ^

uj

— > l- >- o i o o ^

c?£ o a:

a. cr

aUJ

ce

// //' /o\ /J° / oM s~-

Os y

o\/ kp/ <o/ a>/ a> o

<a a

Oj

4> / It-\

CZ^

-/—-—/ ! \ f

§11

.5 <u 3* V> »^ .oCi ° 1 S^SSS? ^ §0)0- §0>lQ

-J - 5?om

3* ^EB:^^"" r\

IT) • 0?

in / // / /

C3 .5 / // 1 // / / / / / f ^

v. /// \ / / // V / "fc \ / i3 1 /

(J 1 o / /

^i o<

I-coo

aa 'ssoi NoissiiAisNVdi oisva
LU

UJ

<n

o

<

I-Q

00

ga 'sso~i NOissiwsNvyi oisva
CO

>-

1- LU

1- _l LU m S z < O o

rr ro

H % H <M

LUO

LU

X

LU <

_l

K

X

On z

COn 2

LU

h-i <z

LU

h-

_i

(0 2 o

en z <l

N > o

_l

Q

a:n

CO o

Z.—) X

CO 2 O o o

(T _l e> z X o

en

X

CO

rr 2

CO <

LU to

a:

LU z X

i—

H < LU tr o 2 o

I- o ^ ^ O o en oo m

00 CO rr to K < LU CD > 1- >- o X o

CO z: o

LUX

LU3

fc?

O

LU

(0 1- tr < li. u_

LL < O cr

EC o Q. a:

LUO

CO

en

aa 'ssoi noissiwsnvui oisva
(S>

LU 2

cr

—

W uj < lu x * b u_ ^ o

(/) UJ Q

OO

O,

CDCOQ<

rr

Q cr o < <

u_ tr UJ

7" UJ O _i >

1- < h- c > I- o

UJ -z. UJ

rr UJ u_

rr 2 u. o o UJ o Q.X

UJ UJ o"-* ^ < <

lcn

52 1 ^ 1 ^ \ 5"

S2 1 ?

v.a* I NT 5 1

So* 1 Q 1 ^

0) o sio °" <

lO

Q.

.tt, 1

itiol

angle a

mosphere

is

atmosphere ^ o

t= oc

_c

—

CP o Oc

<Do

Q.X

\/en

aircraft

the

distance co

c:

<uoco '

Fora

gi

horizon, the

dis

UJ

rrUJxO2

UJQ<

rro

Q.X

UJ

UJo

COQ

UM » 'PV
<

UJ

o

o

cd

(TUJ>

o

Q x

— cr 3

5

<

o

Q

CO

cc

ujIUJo ^

9 i"

\- >- — LlI oUJ

cc

LL

1> 1

to

^1V — —

00 __

ro ___

II

II "5 s;

'J-

.

in ^__^

fax/ma

where

Unima

where

CO „

en

** <

II ~" c

*v

<

ccu

cc

o

cc

UUJu

-z. <

co

SU313IAI '1H9I3H VNN31NV 9NIAI303U
XH

cr<

UJoo2

CO<

CO

IT

UJ or 1- hi UJ > ^ o o o :> o m

<l If)

m 2

1^- l^ 2 1— >- 2 X

iii

Q

UJX 3

^: UJ < 1- q: Ll u_ < <

rr > u

or

X < <oo

u_<

(EO

CE CM <

C\J

ID 2 3 o CT en u. u.

UJuz<

HCOQ

Scd313IAI '1H9I3H VNN31NV 9NIAI333H
X

I-<

LU

o

o

CO<

LU>

o

X

<

o

Q

co

orUJ

iUJo ^

o ^

Q. oo

= 5

UJ 3

LU I- a- <

oro

or

u.<

oru

or

o

oru.UJo

COQ

SH313IAI '1H9I3H VNN31IW 9NIAI3D3U
UJ

cr

z>

£_) UJ

Ill UJ cc o 1-O CO > Z <

UJ

CO

Q CO >- UJ

h-O < H

CO (O

ll cr cr o UJ UJ (O l- >

UJ rr < Ul

Q

CJ<

DC

UJ

1-2

CO

CO

_l 0.

in"

Ul<

CO CO<

CO(O

cr

X

h- CD cr 5

i- in 2

1^- 10

CO Q.

cr <d < Ul > >-

cr

1- 0* Ul hi rr ? O

UJ

u.

UJ CO

ID

O

rr 3 < |— Ul O CD T 1- hi O X COz <

<ru.

UJ

_l

CD<

UlX

(J? UlX

1- CO 5O

_1 < < 23 1 UJ s -1 CO < 1- > z X

u. 23 <

C5 <2

.> 2 <

1—

X 1- 2 z

Ul

cr

UJ <2

CO<

cr

1-

^1

Ul

h-<>

Ul

cr

x-^sh* ———~*7

a- § 1

IS / 8 / 1 -T) / ^ / ^ / ^

NT // 1 I "6 / ^ A/ 

/ ^ / 5 / s

52 3

'v.n1

^J

Ulo

COo

SN0I1VD0H JO ±N3DU3d
LlI O>

UJCO

u.o

UJQ<o

S5

(T> CDCD

CO<

UJ £T O U- UJ

or ujo

co z z < O h- H 22 < Q Oq co -1 >

UJo

orUJ

Q.

CD

>-o

z.

UJO

UJ

cru_

Q

UJ

Q

UJ

crr>o

ui

crco< Q WH lu cr \- ui o hz. ui CO 5 < oo

CO o

CO to o — -1 cr z? o Q o i- w o >

CO

CO o

o"oo

cr LO

h- K' o - CO o

<T o m Qif) <

cr o

ro

ui

—UIX 2 UI

*= => I- < 2 5 2 X < 2 < o y

CO ? 2 > 3 / C / C ( Cs / i / i / 5 / T / 1

r-T—^°

/^? /

1/ * /

I** 1 s

"to //

_fc

—^- i j —"\\T ^» / £ / ) / i / > / 4§ / Ai / ^ / f) "

CM UIo <u 2 3 <1- u

coQ

SN0I1V001 JO lN30U3d
RELATIVE NUMBER OF LOCATIONS RECEIVING SERVICE

FREQUENCY 575 Mc

AIRCRAFT CIRCLING WITH 15 KILOMETERS RADIUS

AT ALTITUDE OF 7500 METERS

RECEIVING ANTENNA HEIGHT MAXIMUM OF

30 METERS WITH DIVERSITY AS REQUIRED

LUO

>

rrLUo

LUU

LU

tr

<o

o

rr

lu

LU>

I-<

_l

LU

LT

320

280

240

200

160

120

/ '50db^\

/ 145 db -^ \ 1

L

b(rr ax) =l40db '

|

1

50 100 150 200 250 300 1

DISTANCE FROM CENTER OF AIRCRAFT CIRCLE, KM

350 400

Figure 26
RELATIVE NUMBER OF LOCATIONS RECEIVING SERVICE

FREQUENCY 785 Mc

AIRCRAFT CIRCLING WITH 15 KILOMETERS RADIUS

AT ALTITUDE OF 7500 METERS

RECEIVING ANTENNA HEIGHT MAXIMUM OF

30 METERS WITH DIVERSITY AS REQUIRED

O

>

cc

UJ

</> o

UJuUJ

cc

</> z.o

I-<o

o

li. o

cc

UJ

CO

UJ>

UJ

cc

320

280

240

200

160

/ l50db-^\

I45db^\ 1

Lb(moxj = l40db^

\.

100 150 200 250 300 DISTANCE FROM CENTER OF AIRCRAFT CIRCLE, KM

350 400

Figure 27
RELATIVE NUMBER OF LOCATIONS RECEIVING SERVICE

FREQUENCY 785 Mc

AIRCRAFT CIRCLING WITH 15 KILOMETERS RADIUS

AT ALTITUDE OF 5,000 METERS

RECEIVING ANTENNA HEIGHT MAXIMUM OF

30 METERS WITH DIVERSITY AS REQUIRED

LUO

>

rr

LU

LUu

LU

en

<o

o

LU

CD

LU>

LU

rr

320

280

240

200

160

120

/I50 db \

145 db'

bfmox j = l40db^

50 100 150 200 250 300 DISTANCE FROM CENTER OF AIRCRAFT CIRCLE, KM

350 400

Figure 28

U.S. DEI \RTMENT OF COMMERCE

I derick H. Mueller, Secretary

\ noNAL rn hi i \d\rds

A. V. Asti Director THE NATIONAL BUREAU OF STANDARDS

The scope of activities of the National Bureau of Standards at its major lahoratories in Washington. D.C., and

Boulder, Colorado, is suggested in the following listing of the divisions and sections engaged in technical work.

In general, each section carries out specialized research, development, and engineering in the held indicated \>\ its title. A brief description of the activities, and of the resultant publications, appears on the inside of the front

cover. WASHINGTON, D.C.

Electricity and Electronics. Resistance and Reactance. Electron Devices. Electrical Instruments. Magnetic Measurements. Dielectrics. Engineering Electronics. Electronic Instrumentation. Electrochemistry.

Optics and Metrology. Photometry and Colorimetry. Photographic Technology. Length. Engineering

Metrology.

Heat. Temperature Physics. Thermodynam

Radicals Research.

oogenic Physics. Rheolog\ . Molecular Kinetics. Free

Atomic and Radiation Physics. Spectroscopy- Radiometry. Mass Spectrometrv. Solid State Physics. Electron Physics. Atomic Physics. Neutron Physics. Radiation Theory. Radioactivity. X-rays. High

Energy Radiation. Nucleonic Instrumentation. Radiological Equipment.

Chemistry. Organic Coatings. Surface Chemistry. Organic Chemistry. Analytical Chemistry. Inorganic

Chemistry. Klectrodeposition. Molecular Structure and Properties of Gases. Physical Chemistry. Thermochemistry. Spectrochemistry. Pure Substances.

Mechanics. Sound. Mechanical Instruments. Fluid Mechanics

Capacity, Density, and Fluid Meters. Combustion Controls.

I'litrineering Mechanics. Mass

Organic and Fibrous Materials. Rubber. Textiles. Paper. Leather. Testing and Specifications. Poly- mer Structure. Plastics. Dental Research.

Metallurgy. Thermal Aletallurgy. Phvsics.Chemical Metallurev. Mechanical Metallurgy. Corrosion. Metal

Mineral Products. Engineering Ceramics. Glass. Refractories. Enameled Metals. Constitution and Microstructure.

Building Technology. Structural Engineering. Fire Protection. Air Conditioning, Heating, and Refrigeration. Floor, Roof, and Wall Co\erings. Codes and Safety Standards. Heat Transfer. Concreting Materials.

Applied Mathematics. Numerical Analysis. Computation. Statistical Engineering. Mathematical Physics.

Data Processing Systems. SEAC Engineering Group. Components and Techniques. Digital Circuitry.

Digital Systems. Analog Systems. Application Engineering.

• Office of Basic Instrumentation. • Office of Weights and Measures. BOULDER, COLORADO

Cryogenic Engineering. Cryogenic Equipment. Cryogenic Processes. Properties of Materials. Gas Liquefaction. Radio Propagation Physics. Upper Atmosphere Research. Ionospheric Research. Regular Propagation

Services. Sun-Earth Relationships. VII F Research. Radio Warnini; A irglow and Aurora. Radio

Astronomy and Arctic Propagation.

Radio Propagation Engineering. Data Reduction Instrumentation. Modulation Research. Radio Noise. Tropospheric Measurements. Tropospheric Analysis. Propagation Obstacles Engi Radio-Meteorology. Lower Atmosphere Physics.

Radio Standards. High Frequency Electrical Standards. Radio Broad; [uencj Im- pedance Standards. Electronic Calibration Center. Microwave Physics. Microwave Circuit Stand

Radio Communication ami Systems. Low Frequency and Very Low Frequency I ;h Fre- quency and Ver\ High Frequeno Research. Ultra High Frequency and Super High Frequency Rese adulation Research. Antenna Research. Navigation Systems. Syst >ns.
NBS