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THE NBS

METEOR-BURST PROPAGATION PROJECT

- A PROGRESS REPORT

BY

CHARLES E. HORNBACK, LOUIS D. BREYFOGLE, AND

GEORGE R. SUGAR

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

Functions and Activities

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 pro\ ides

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 Scries,

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 ^Vtote

No. 86

March 31,, i960

THE NBS METEOR-BURST PROPAGATION PROJECT - A PROGRESS REPORT

Charles E. Horriback, Louis D. Breyfogle, and George R. Sugar

This work has been supported in part by the Wright

Air Development Center under DO (33-6l6) 58-16, and

the Air Force Cambridge Research Center under

CSO&A 59-52^.

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 $1.25

CONTENTS

PAGE

1. INTRODUCTION 1

2. EXPERIMENTAL ARRANGEMENTS 2

3. DATA CONTROL 7

k. DATA INTERPRETATION 10

5. SUMMARY 37

6. APPENDIX. COMPUTER PROGRAMS FOR DATA ANALYSIS .... 39

7. REFERENCES

^

THE NBS METEOR-BURST PROPAGATION PROJECT - A PROGRESS REPORT

by

Charles E. Hornback, Louis D. Breyfogle, and George R. Sugar

ABSTRACT

This report briefly describes a meteor-burst propagationstudy program at NBS-Boulder Laboratories and presents some of

the preliminary analysis results. Observations have been made

with scaled systems over three different paths (Long Branch - Table Mesa, Norman - Fargo, and Barrow - Kenai) at frequencies

of 30, 50, and 7^ Mc/s. The recorded data is processed by a combination of manual and automatic methods. The preliminary

results show about a 10 db diurnal variation in threshold for

a constant duty-cycle. Thresholds for a constant duty-cycle

were observed to have an approximate frequency dependence

relative to 30 Mc/s of 15 db lower for 50 Mc/s and 30 db lower

for 7^+ Mc/s. There was no statistically-significant difference

observed in the occurrence of meteor-bursts from a Poisson

distribution.

THE NBS METEOR-BURST PROPAGATION PROJECT - A PROGRESS REPORT

bv

Charles E. Horriback, Louis D. Breyfogle, and George R. Sugar

1. INTRODUCTION

The meteor-hurst propagation project described in this report was conceived during the early part of 1956. At that time, it -was planned

to make an extensive study of meteors to determine their communications

utility. The instrumentation required for this study -was elaborate - as a consequence, data taking did not begin until September 1959*

The original plan for the experiment was tc make measurements,

on a routine basis, of meteor-burst signal amplitudes over several

oblique paths, at several frequencies in the VHF range. Automatic data

recording and reduction techniques based on the use of medium size electronic digital computer (IBM 650) were planned in order to handle the

large volume of data required to obtain statistically significant results. The field recordings were to be made in such a manner as to

permit the later reproduction of the amplitude fluctuations of each

burst signal. This method was chosen to allow very great flexibility

in data analysis. The work has been proceeding along these lines, and

this report is designed to bring the reader up to date on the operation

of the project.

The first portion of the report will be devoted to the equipment

aspect, the second part to the data analysis and preliminary results.

It is assumed that the reader is familiar with the basic concepts of

meteor-burst propagation and communication [1, 2., 3].
-2-

2. EXPERIMENTAL ARRANGEMENTS

2.1. Transmission Paths

Three basic transmission-reception paths (Long Branch - Table

Mesa, Norman - Fargo, and Barrow - Kenai) were established as shown in

Figure 1. The details of these paths are tabulated in Table 1.

The two paths in the central United States are arranged so that

they cross near their midpoints. This arrangement was chosen to simplify studies of the effects of path orientation on the meteor-burst

charact eri st i cs

.

The Barrow - Kenai path was established to allow a comparison of

meteor-burst activity in the arctic regions with the activity in the

temperate regions. This path will be used primarily to determine those

characteristics of meteor-burst propagation which are peculiar to the

arctic region.

2.2. Field Station Equipment

One of the primary prerequisites to data comparisons between different paths is the maintaining of "scaled systems"; that is, systems

as nearly identical as possible at all locations and on all frequencies

of operation. Special attention has been given to system scaling in

selecting and setting up the experimental paths.

The antennas used at all field sites are horizontally-polarized

five-element Yagi antennas located 2.k wavelengths above the ground and

tilted along their boom axes at an angle of kO degrees relative to the

ground. The Ho degree tilt angle suppresses the ground-reflected com- ponent and thus provides a more uniform radiation pattern than would be

possible with a horizontal Yagi antenna. Figure 2 shows a comparison

of the patterns of the tilted and horizontal antennas.

The transmitters at the Long Branch, Norman, and Barrow field sites are continuous -wave transmitters operated at 2 kilowatts output on each

frequency (30, 50, and r jk Mc/s) . (Since December 2, 1959, the 7^ Mc/s

transmitter at .Long Branch has been operated at 10 kilowatts output.)

The system scaling is maintained by correcting the data for transmitter

power output differences and transmission line losses.
-3-

The receiving sites at Table Mesa, Fargo, and Kenai all utilize

similar equipment. The receivers used are special WBS-designed units

which have a 300 cycle bandwidth and a logarithmic amplitude response

characteristic. Daily calibrations are made on all receivers. All

calibrations are referred to 1 microvolt open-circuit at the antenna

terminals (50 ohm impedance).

Two general types of recording media are used at the receiving

sites. The meteor-burst data recordings are taken on seven-channel

punched paper tapes produced by a digital recorder [5]. Each recorder

has three similar but independent channels. The data for each of the

three operating frequencies are sampled, digitized in a binary form,

and recorded on a separate punched tape. In addition, strip-chart recordings are made at each frequency in order to provide a graphic rec- ord of the overall system performance. In order to present a clearer

indication of the scatter signal, the strip-chart recorders have a 12-

second time constant in their input circuits.

Two modes of operation of the digital recorder are currently being

used. The first, the so called "start-stop" mode, utilizes a threshold

unit (external to the recorder) to supply the start-stop pulses to con- trol the recorder. In this mode of operation, data is punched out only

when the incoming signal exceeds a manually set threshold. Since meteorburst signals exhibit considerable fading, the threshold unit includes

circuitry to keep the recorder from stopping during brief signal fades.

In order to more accurately reproduce the sharp leading edge of the

burst signal, the first five samples are spaced close together in time.

The remaining samples are more widely spaced, the sampling continuing

as long as the signal is present. The first sample of a meteor-burst

record is taken within 10 milliseconds of the start of a burst. The

first sample and four additional samples make up the "fast" samples that

are taken at the beginning of each signal burst. These samples may be

taken at a rate of 200, 100, or 50 samples per second. The remaining

samples are taken at a rate of 20, 10, or 5 samples per second. At the
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-7-

end of each burst record, the recorder records the time, and stops to

wait for the next burst.

The second mode of operation is the "continuous sampling" mode.

No threshold is used; the recorder runs continuously, recording the

signal variations -which are fed to it from the receivers. Continuous

sampling is performed at rates of 20, 10, or 5 samples per second.

The receiving and recording equipment is calibrated daily with a standard c-w signal generator connected at the receiver input terminals.

A calibration tape is punched out by the recorder as the calibrations

are made. In addition, a separate "internal test" is made daily to determine the overall condition of the digital recorder.

The digital recorder is currently being operated for a period of

l6 minutes of each hour. The strip-chart records are being taken for

a full 2k hours per day.

3. DATA CONTROL

The flow of data from the field stations through the various

stages of processing is represented by the diagram shown in Figure 3«

The effective control of the data processing has required a large

amount of detailed record keeping. Considerable time has been spent

from October 1959^ to present, in developing the processes for data

control.

3.1. Logging of Records

Records received daily from the three receiving stations are:

1. station log-sheets,

2. calibration tapes,

3. recorder test tapes,

h. data tapes, and

5. strip charts.

Transmitting stations send in their station log-sheets. Norman and

Barrow also send strip charts showing a continuous record of the power

transmitted.
-8-

FIELD STATIONS

RECEIVING

1. Table Mesa

(Boulder,, Colorado)

2. Fargo, North Dakota

3. Kenai, Alaska

TRANSMITTING

Long Branch, Illinois

Norman, Oklahoma

Barrow, Alaska

NBS (Boulder)

Preliminary logging in of data records

Manual reading & scaling of: Automatic processing of:

1. Strip charts 1. Recorder test tapes

2. Transmitter logs 2. Calibration tapes

Manual preparation of data for automatic

processing

Automatic processing

Final processing (e.g. plotting)

Figure 3 SEQUENCE OF METEOR-BURST DATA PROCESSING
-9-

3.2. Recorder Test and Calibration Tapes

The test and calibration tapes are processed as soon as they are

received. Errors in each test tape are identified and a tape-condition

report is sent to the field station. The calibration tape processing

produces calibration cards (Hollerith cards) -which relate recorder

scale values to signal levels at 5 clb intervals from -ko to +kO db.

3.3. Strip Charts

There is a strip chart made for each signal frequency recorded at

each station. These charts are records of the same receiver signal

which goes into the digital recorder and are used to provide a visual

indication of the character of the received signal. Each chart is

scaled for noise level and scatter signal level. A record is kept for

all unusual (e. g. sporadic E) and unusable (e. g. transmitter off) signal data. This information is used to help determine -which data tapes

should be processed and how they should be edited. In essence, the

strip charts are the main source of information used in the quality

control of the data.

3.^+. Systems Corrections

All the data are normalized relative to a 1 microvolt (open circuit) signal at the receiving antenna terminals and a power of 2 lew delivered to the transmitting antenna terminals, by correcting for transmission line losses and for the transmitter power output variations.

The line losses for the field stations have been measured to within 0.1

db except at Barrow and Norman where line loss estimates have been made

knowing the lengths and types of line involved. The transmitter power

output variations are determined from the transmitter logs to within

0.1 db and are combined with the line losses to give a total correction

which is rounded to the nearest decibel. This total correction is then

used to normalize the observed signal strength values.

3.5. Preparation of Data for Automatic Processing

The preparation of data tapes for machine processing requires

that all of the information from the station log-sheets, the test tapes,

and the strip charts be assembled, that the tapes be edited, and that
-10-

processing control cards (power corrections, identification, etc.) "be prepared. The data tapes are then processed in the computer. The results, on punched cards, are further processed either by additional

automatic computation, by plotting, or by some form of manual processing of the card listing.

3.6. Data Summary

A summary of the data "which have been taken by the field stations

from September 1959 to March i960 is shown in Table 2. Note that the

symbol F (used in Table 2) for faulty data does not always mean that

useful information cannot be obtained from the tape records, but rather,

that more than the ordinary processing procedures are required to obtain

the information.

k. DATA INTERPRETATION

Several questions arise in attempting to reduce the recorded data

to meaningful numbers which describe meteor-burst characteristics. The

two principle questions are:

1. Which of the measurable characteristics are most useful for

determining the communication capability of meteor-burst signals?

2. How should the values of these characteristics be presented?

Some approaches to answering these questions are discussed below.

^-.1. The Nature of the Received Signals

There are at least five kinds of signals which are observed:

1. galactic noise,

2. D-scatter,

3. meteor-burst signals,

h, enhanced signals such as Es, and

5. interference.

Figure k shows a sample of a strip-chart taken at Table Mesa at 30 Mc/s

using a 12-second recorder time-constant. This is a record of the re- ceived signal strength from 0600 to 06^-5 and from 09*40 to 1100 on
-11-

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October 28, 1959* The two-minute "noise breaks" at each hour and half

hour show the levels of galactic noise (at 0600 and 0630) or an interfering signal (at 1000 and 1030) if present. In this example, the

scatter-signal level is 10 to 20 db ahove the galactic-noise level.

The relatively large meteor-burst signals appear as the spikes which

show above the scatter level. The interference-signal level is about

10 db above the galactic-noise level, (in this case, the interference

is not strong enough to affect the desired data.) Other kinds of signals appear on the strip-charts, such as sporadic-E signals which appear as a very high continuous signal level or aurorally reflected signals which often appear as a thin trace on the chart. Examples of

these signal records are not shown in this report but are similar to

those shown in Figures 2k and 32 of Bailey et al. [6],

Since various modes of propagation are observed, one problem is

to decide where to set the system threshold in order to observe relatively pure meteor-burst signals. The criterion for establishing the

observing threshold level has been obtained by studying the probability

distribution of the received signal strengths. Figure 5 shows an ex- ample of a Rayleigh plot made for Table Mesa data taken on October 31*

1959 at 1200 hours. The plot shows the cumulative distribution of signal strength for each of the three observing frequencies. Scatter signals are known to have a Rayleigh distribution [7]» In Figure 5 these

would be represented by a straight line with a slope of -1. The

straight lines in Figure 5 labelled 30, 50, and 7^ Mc/s represent Rayleigh distributed signals having the same median values as the observed

signals. If there were no meteor-burst signals, the curves of Figure 5

would represent the scatter only and would follow the straight lines in

the upper direction and bend away from the straight line in the lower

direction, as the example curves do because of noise contamination.

The fact that the actual curves bend away from the straight line in the

upper direction is attributed to the presence of meteor-burst signals

since meteor-burst signals are not Rayleigh distributed.
-1kThis difference In distribution provides the method for selecting

meteor-burst signals for analysis. The duty cycle of a Rayleigh distributed signal is 0.1$ at 10 db above its median (0.01$ at 11 db above

the median) . Therefore, if the observing threshold for meteor-burst

signals is set 10 db above the signal median there -will be very little

contamination of the burst data by scatter signals. Hence, in the ex- ample of Figure 5> the threshold levels for observing meteor signals at

30, 50, and 7^ Mc/s should be 5 + 10 = 15 db, -17.5 + 10 = -7. 5 db, and

-26.5 + 10 = -I6.5 db respectively.

The diurnal variation in the median signal Is illustrated in Figure 6 which shows the weekly medians of the hourly-median signal levels

for some Fargo data. (These should not be interpreted as representing

scatter propagation since there is substantial noise and meteor-burst

contamination of some of the values.) There appears to be more diurnal

variation in the median signals for Fargo than for either Table Mesa or Kenai.

Thresholds used for the start-stop mode of operation on 50 and 7^

Mc/s are set to be 10 db above the highest scatter-signal levels. (The

7^- Mc/s signal medians are primarily noise.) Similarly chosen thresholds are used when analysing the continuous mode data. By using these

fixed thresholds, results such as the long-term variation of meteor

rates can most readily be obtained. At 30 Mc/s, the presence of relatively strong signals having a non-meteoric propagation mode has interfered with the normal operation of the recording system in the startstop mode. As a result, only continuous -mode data is taken at 30 Mc/s

and a floating threshold is used by the analysis program.

J+.2. Duty Cycle

Duty cycle is the percentage of time that the observed signal

strength is greater than a given signal level. To a first approximation, the duty cycle is a measure of the time available for communicating by means of meteor-burst propagation, and is therefore, a useful

parameter to obtain. The actual useful time is, of course, dependent
-15-

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0.01 0.1 1.0 10 90 99 DUTY CYCLE IN PERCENT

99.9 99.99

Figure 5 RAYLEIGH PLOT OF SIGNAL LEVEL VERSUS DUTY CYCLE
-16-

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12 90° WEST TIME16 20 24

MEDIANS OF THE HOURLY-MEDIAN SIGNAL LEVELS, FARGO,

NOVEMBER 27 THROUGH DECEMBER k, 1959
-17-

on equipment parameters as well as propagation characteristics.

Figure 7 through 11 illustrate the variations in the weekly medians

of duty cycle observed for various levels and frequencies. Figure 8

shows the diurnal variation quite well with a maximum near 0600 hours

and a minimum near 1800 hours. The times of maxima and minima generally agree with previous observations [3]«

Several features should be pointed out in these duty-cycle curves.

1. Figures 7 through 9 are for one set of data taken at Table

Mesa. Each plot is for a different frequency, and the differences between duty cycles at the various frequencies are apparent. These data

indicate that at a given duty cycle the signal level is 15 db lower" at

7^ Mc/s than at 50 Mc/s and 15 db higher at 30 Mc/s than at 50 Mc/s.

2. Figure 7 shows the effect of high mid-day scatter signals on the 30 Mc/s duty cycles. The duty cycle data for 5j 10, and 15 db signal levels are missing here since the high scatter levels have obscured

the meteor-burst observations.

3. Figure 10 shows the duty cycles observed on 50 Mc/s at Fargo.

If these data are compared with the corresponding data from Table Mesa

(Figure 8), it is apparent that there are distinct differences in their

diurnal variations. The extent to which these differences are associated with path orientation is not known since the two sets of data were

taken at different times.

k. Figure 11 shows the duty cycles observed on 50 Mc/s at Kenai.

The most interesting feature of these data is the absence of the pronounced morning maximum which is apparent in the Fargo and Table Mesa

data. Further data should demonstrate whether this kind of diurnal

variation is a permanent characteristic of the Barrow-Kenai path.

5. It can be seen from Figures 7 through 11 that rather large

hour-to-hour variations in duty cycle are present. Other data indicate

a variation in duty cycle, at a given hour of the day corresponding to

about a 10 db range of threshold levels. Figure 12 is a mass plot

illustrating the spread of hourly values.
-18-

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Figure 7 MEDIANS OF THE HOURLY DUTY-CYCLE VALUES FOR INDICATED

THRESHOLDS RELATIVE TO 1 MICROVOLT (50 OHMS),

TABLE MESA, OCTOBER 31 THROUGH NOVEMBER 8, 1959,

30 MC/S.
-19-

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Figure 8 MEDIANS OF THE HOURLY DUTY-CYCLE VALUES FOR INDICATED

THRESHOLDS RELATIVE TO 1 MICROVOLT (50 OHMS) , TABLE MESA, OCTOBER 31 THROUGH NOVEMBER 8, 1959,

50 MC/S.
-20-

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Figure 9 MEDIANS OF THE HOURLY DUTY-CYCLE VALUES FOR INDICATED

THRESHOLDS RELATIVE TO 1 MICROVOLT ( 50 OHMS) , TABLE MESA, OCTOBER 31 THROUGH NOVEMBER 8, 1959,

7^ MC/S.
-21-

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Figure 10 MEDIANS OF THE HOURLY DUTY-CYCLE VALUES FOR INDICATED

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-22-

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Figure 11 MEDIANS OF THE HOURLY DUTY-CYCLE VALUES FOR INDICATED

THRESHOLDS RELATIVE TO 1 MICROVOLT ( 50 OHMS) , KENAI, NOVEMBER 23 THROUGH DECEMBER 1, 1959; 50 MC/S.
-23-

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Figure 12 MASS PLOT OF 100$-INTERCEPT VALUES, TABLE MESA,

DECEMBER 15 THROUGH 30, 1959, 50 MC/S
-2kThe variation of duty cycle versus threshold for one observing

period at Table Mesa is illustrated in Figure 13. It can be seen that,

for duty cycles less than 50%, this relation between duty cycle and

threshold can be approximated by a straight line. These lines can be

represented by the equation

D = m (ST/20 - S/20) (l)

where D is the logarithm of the fractional duty cycle, m -is the magnitude of the slope of the line, S. is a reference signal level in decibels, and S is the signal level in decibels. The slope m and reference

signal level S define the line. S_ is the lOOfo-intercept, i. e. when

S equals S.. , the duty cycle equals 100$. Equation (l) corresponds to

the more conventional duty cycle relation [8]

,m d/100 = (s^sr (2)

where d is the duty cycle in percent, s is the reference signal voltage, and s is the signal voltage.

Hourly slope and 100$-intercept values have been computed for sev- eral weeks of data by performing a least squares fit of a straight line

to the data for each hour. The data points used were only those in the

range from 10 db above the median signal strength to the signal strength

corresponding to 0.05$ duty cycle. Figures ik through l6 show plots

of weekly medians of hourly-slope values for Table Mesa, Fargo, and

Kenai. Most of the 50 and 7^ Mc/s slope values are in the range of 1.

5

to 2.0 and show little diurnal variation. The 30 Mc/s slope values

show considerable diurnal variation and are usually greater than 2.0.

This result indicates [8] that these 30 Mc/s test circuits are poorly

suited for a meteor-burst communication system.

It appears that the observed values of the 30 Mc/s slopes are strongly influenced by the scatter signal levels. The relatively high
-25-

100

0.5 —

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SIGNAL STRENGTH IN DECIBELS (UNNORMALIZED)

20 30

Figure 13 DUTY CYCLE VERSUS SIGNAL STRENGTH
-26-

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Figure Ik MEDIANS OF THE HOURLY-SLOPE VALUES, TABLE MESA,

OCTOBER 31 THROUGH NOVEMBER 8, 1959
-27-

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Figure 15 MEDIANS OP THE HOURLY-SLOPE VALUES, FARGO, NOVEMBER 27

THROUGH DECEMBER k, 1959

-29-

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Figure 16 MEDIANS OF THE HOURLY-SLOPE VALUES, KENAI, NOVEMBER 23

THROUGH DECEMBER 1, 1959
-30-

scatter levels at 30 Mc/s obscure the -weaker meteor-burst signals and

thus increase the proportion of signals received from overdense trails.

To check this point, slopes were computed using only those data points

which fell above a high and constant threshold (+17 db) . These slopes

are shown in Figure Ik and are consistent with the above hypothesis.

Figure 17 shows medians of hourly 100$>-intercept values for 30,

50, and 7^ Mc/s observations at Table Mesa. The diurnal variation here

is apparent. The day-to-day variability of the intercept is illustrated by the mass plot shown in Figure 12. (it has recently been found

that the lfo-intercept value is a more reliable measure of meteor activity, and therefore in future work it will be computed and used in place

of the 100/o-intercept.)

^.3« Meteor-Burst Rates and Durations

Meteor arrival rates vary from hour to hour and day to day with a short-term variation in rate which is thought to be Poisson distributed;

i. e. if the time intervals between meteor arrivals are measured, the

probability density function of these time intervals will be given by

p(n) = n exp(-nt) (3)

where n is the average rate of the meteor occurrences and t is the time

interval. The distribution function is obtained by integrating equation (3) , and is

oo P(t > T) = n J exp(-nt) dt = exp(-nt) (k)

T

where T is the minimum time-interval being considered. This is the

probability that the time interval between bursts will be greater than

or equal to a given time T. Note that a plot of the logarithm of

P(t > T) versus T results in a straight line.

Before proceeding, it is useful to define some terms used in the

analysis of meteor-burst rate and duration data. These are defined
-31-

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Figure 17 MEDIANS OF THE HOURLY 100$-INTERCEPT VALUES, TABLE MESA,

OCTOBER 31 THROUGH NOVEMBER 8, 1959
-32-

with reference to a threshold -which is at least 10 db above the median

signal level. The definitions are as follows:

1. Rump - An excursion of the signal above the threshold level.

For example, in Figure l8, the signal excursions between times t and

t

p

, t and t, , t and t^, and to and t are called "humps".

2. On-Time - The time interval spanned by a hump. For example,

in Figure l8, the time interval t

p

minus t is the "on-time" for hump A.

3. Off-Time - The time interval between two adjacent humps. For

example, in Figure l8, the time interval t„ minus t is the "off-time"

between humps A and B.

k. Elapsed-Time - The time interval between the beginning of

adjacent humps. For example, in Figure l8, the time interval t_ minus

t. is the "elapsed-time" between humps A and B.

Several hours of data have been processed to obtain an indication

of elapsed-time, on-time, and off-time distributions. Figures 19 and

20 show examples of these results. The data used were from 50 Mc/s observations at Table Mesa and appeared to be similar to data for other

hours, frequencies, and stations.

On-time distributions are similar in shape from hour to hour, however, the number of on-times greater than a given on-time can vary over

a 10 to 1 range. This variation must be due in part to variations in

meteor-rates, meteor-trail orientations, and ionospheric wind-shears.

Elapsed-time distribution curves show two main features: 1. for

elapsed-time intervals less than 3 seconds, the elapsed-time curve bends sharply upward; and 2. for elapsed-time intervals greater than 3 or h seconds, the elapsed-time curve is nearly a straight line. The

upward bend of the curve appears to result from the multiple humps of

fading meteor-burst signals such as shown for burst B of Figure l8. If

all bursts were non-fading, then the upward bend of the curve would

probably not be present. The straight-line portion of the curve appears

to be associated with the time intervals between the meteor -bursts

themselves.
-33-

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NOTE"-

I. THE OBSERVATION TIME FOR THIS DATA IS 13 MINUTES

2 THE OFF AND ELAPSED" TIME DISTRIBUTIONS ARE FOR

ON- TIMES > 0.2 SECONDS

3. THRESHOLD = -5db RELATIVE TO l^tV, 50fl

4. NOISE LEVEL = -26 db (300 CPS BANDWIDTH)

I I I I t I l I I I I I I I I I I I I I I I I

10 12 14 16 18 20

TIME INTERVAL IN SECONDS

22 24 26 28 30

Figure 19 ON-TIME, OFF-TIME, AND ELAPSED-TIME DISTRIBUTIONS,

TABLE MESA, OCTOBER 2k, 1959, 0^00 HOURS, 50 MC/S
100

-35-

50

NOTE:

1. OBSERVATION TIME IS 16 MIN.

2. DATA SAMPLING RATE IS 20/SEC.

3. THRESHOLD = - 8 DB RELATIVE TO IjiV, 50fl

4. NOISE LEVEL = -27 DB (300 CPS BANDWIDTH)

5. n = 0.0302 METEORS/SEC. OR 109 METEORS/HOUR

4

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5 10 TIME INTERVAL IN SECONDS13

Figure 20 ON-TIME AND ELAPSED-TIME DISTRIBUTIONS, TABLE MESA,

FEBRUARY 2k, i960, 2000 HOURS, 50 MC/S
-36-

An estimate of meteor rate, based on the elapsed time distributions,

may be made if it is assumed that the intervals between bursts are Poisson distributed and that the inclusion of data for fading bursts does

not seriously alter the slope of the basic Poisson distribution. (The

validity of these assumptions is being investigated.) The following

procedure is used. The elapsed-time data for intervals greater than 3

seconds are fitted by a straight line. The slope, n, of this line is

then taken to represent the meteor-burst rate, using the relation

5 . . in P(t ft T) __ .^ l°g P(t 2; T)

(fl

which was obtained from equation (k) • By applying this procedure to

the data of Figure 20, it is found that the meteor rate was 109 per

hour for an observing threshold of -8 db.

The off-time curve of Figure 19 shows the distribution of time intervals between humps rather than the intervals between the beginnings

of humps (e lapsed-times) . The off-time and elapsed-time curves are es- sentially the same for interval times greater than about 10 seconds.

The sharp upward bend of the curve at intervals less than 2 seconds em- phasizes the fact that the intervals between the humps of a burst are

quite brief. These data suggest that typical fading rates are between

2 and 10 cps.

One of the problems which concern the users of a meteor-burst com- munication system is how long must one wait in order to be able to make

a single transmission of a specified length. Such waiting-time information is being evaluated in detail. One can obtain a rough estimate

of the probability of successful transmission by using information such

as that given in Figure 20. As an illustration, consider the following

example: Suppose that the system uses a 50 Mc/s frequency and a threshold of -8 db, and one wishes to know what the probability is of obtaining a 0.2 second transmission interval while waiting no longer than 60

seconds. Assume that the on-time and elapsed-time distributions are
-37-

independent . Then the desired probability is just the product of the

probabilities that there -will be a meteor-burst -within 60 seconds and

the probability that the on-time will be at least 0.2 seconds. From

Figure 20, it is found that the former probability is 0.8l and the latter 0.^8. Thus the probability of a successful transmission is 0.39*

5. SUMMARY

Meteor-burst data have been recorded digitally on paper tape and

continuously on strip charts for three frequencies (30, 50, and 7^ Mc/s) over three paths (Long Branch - Table Mesa, Norman - Fargo, and Barrow

- Kenai) . By means of the strip-chart recordings, station log-sheets,

and calibrations, the digital data tapes are 'prepared for automatic

processing. The results of the duty cycle and meteor-burst elapsedtime analyses are punched on Hollerith cards.

Meteor-burst duty-cycle data, when plotted in a coordinate system

of logarithm of duty cycle versus signal strength in decibels, lie along

a straight line which may be described by two parameters, slope and 100$-

intercept. Slope and 100^-intercept values have been obtained by the

method of least squares fitting of a straight line to the data. The

slope values for 50 Mc/s and 7^ Mc/s are usually between 1.5 and 2.0,

while for 30 Mc/s, values are usually greater than 2.0. Therefore, 30

Mc/s systems are considered to be poor choices for meteor-burst commu- nication purposes [8]. The Table Mesa and Fargo 100$-intercept data

show about a 10 db diurnal variation in the observing threshold which

has a maximum in the morning and a minimum in the afternoon. Kenai data

do not show a significant diurnal variation. The threshold for observing a fixed duty cycle shows a frequency dependence such that a 15 db

higher threshold should be used to observe 30 Mc/s signals than for 50

Mc/s and 30 db higher threshold for 30 Mc/s than for 7^ Mc/s.

Meteor-burst elapsed-time data (elapsed-times are the time intervals between meteor bursts) are presented for signal bursts whose

durations above a given threshold are greater than 0.2 seconds. Plots
-38-

of the logarithm of the number of elapsed time-intervals which exceed

a given time interval versus the time interval show that the data lie

along a straight line and, therefore, fit a Poisson distribution. If

one assumes the data are Poisson distributed, the slope of the distribution line is the meteor rate for the observing period.

The authors wish to acknowledge the help and guidance of Kenneth

L. Bowles and Ralph J. Slutz, and also, the work of the many people at

the various field stations and the NBS-Boulder Laboratories who have

obtained and analyzed the data.
-39-

6. APPENDIX. COMPUTER PROGRAMS FOR DATA ANALYSIS

Data, calibration, and test tapes are analyzed by means of computer programs. The computer is equipped with a paper-tape reader -which

reads the tape characters under control of the computer program. The

calibration program produces a calibration card which has signal scale

values (0-99) corresponding to every 5 db level from -kO db to +*40 db.

The test-tape program produces error cards whenever an error is detected in the test -tape.

6.1. Kinds of Programs

There are several kinds of data-analysis programs which may be

grouped into "basic" reduction programs and "secondary" reduction

programs.

The basic-reduction programs are used to process the data tapes

and give intermediate results in the form of punched cards. Three of

these programs which have been developed are:

1. HUMP (Detects the maxima and minima of the signal-strength

data) . This program reads the characters from either start-stop or continuous data tapes and punches a card for each time a maximum or minimum is detected in the sequence of data samples. Each card punched

at a maximum indicates the interval of time during which the signal

strength was lower than a threshold value; there are ten such intervals

on each card corresponding to ten thresholds. These span a 50 db range

in signal strength in five decibel steps. Each card punched at a minimum indicates the interval of time (measured from the previous card)

during which the signal was greater than the threshold valuej there are ten such values on each card corresponding to the same thresholds used

for the maximum card.

2. MTM (Produces a card for each recorded meteor-burst signal)

This program is used primarily to analyze the start -stop data tapes. A

card is punched for each meteor-burst signal as defined by the recording equipment. Information punched on the card includes:
JtO*

(1) the time at the beginning of the meteor-burst to the

nearest second,

(2) the elapsed-time to the beginning of this burst since

the beginning of the previous burst,

(3) the maximum value of the signal during the burst, and

(k) the total amount of time the signal was above a given

level for ten different signal levels -which span a 50

db range in 5 ctb steps.

At the end of each hour of data, a set of three cards is punched which

shows the total time that the signal was greater than the various

thresholds and gives the total number of meteor-bursts counted for the

hour.

3. DIST (Forms cumulative distribution of the signal-strength

values, of the elapsed-times, and of the on-times) . Only continuous

data tapes are processed by this program. Three distributions are

formed:

(1) the number of signal-strength samples which are equal to

or exceed a given scale value versus the scale values,

(2) the number of elapsed-time intervals which exceed a given time interval versus the time intervals, and

(3) the number of on-time intervals which exceed a given

time interval versus the time intervals.

The time intervals are measured by means of a threshold, i. e. referring

to Figure 18, burst (c) does not exceed the threshold, therefore, time

t„ would not be measured, but all the other times indicated in the Figure would be measured. For each hour of data, the values of the three

distribution tables are punched on 16 cards.

The secondary reduction programs are used to process the cards

from the basic reduction programs. Several of these programs have been

developed:

1. ANALYSIS OF DIST (Produces an hourly value card for signal

median, slope, intercept, and six duty cycles). This program reads a
-laset of hourly cards into the computer for the distribution of the signal-strength values and performs the following computations:

(1) determines the median of these signal values and converts

this to a normalized decibel value,

(2) computes six duty cycles for six decibel levels which

are separated by 5 db steps, arid

(3) computes by least-squares fit, the slope and 100$ or Vfo intercept of the line which describes equation (2) ,i. e.

d/100 = ( Sl/s)

m

.

These values are assembled and punched on one card for each hour of

data. There are two modifications of this program:

(a) Sectional Slopes - This program computes slopes and

intercepts by least-squares fit of a straight line

for two sections of the signal strength range. The answers are punched on one card for each hour of

data.

(b) Hourly Cards from MTM Cards - This program processes the three hourly summary cards from the MTM program and produces an hourly output card which has

the same information as the output card from the

ANALYSIS OF DIST program.

2. MEDIAN (Finds the medians of the various values on the hourly

cards from the ANALYSIS OF DIST program) . This program reads in a set

of cards (up to 90 cards) and determines the median values of the various parameters on the cards. One output median card is punched for each

set of cards read in.

6.2. Processing Data

Many problems have arisen since we started to process some of the

data in October 1959* For example, a great deal more handwork is re- quired in order to prepare data for the computer than had originally
been expected. Also, some programs are too slow to use if an appreciable amount of data is to be processed. Processing techniques are being

improved so that less handwork is required and processing rates are increased.

One of the big problems is the slowness of the present computer

system. Running times for the basic-reduction programs are:

1. HUMP - requires real time to run, i_. e. l6 minutes of recorded

data requires l6 minutes of computer time.

2. MTM - requires 3 to k minutes per l6 minutes of recorded data.

3- DIST - requires 1.75 minutes per 16 minutes of recorded data

(recorded at 5 samples per second)

.

Running times for the secondary-reduction programs are considerably

faster and present no immediate problems.

Because of the slow running time, only about two days of data on three frequencies have been run on the HUMP program. However, this

program produces the most detailed description of the received signals.

About one week of data was run on the MM program; however, without the angle information, this program produces very little more than

the DIST program. Most of the data has, therefore, been reduced by the

DIST program. About 12 weeks of data have been processed.

Obviously all of the recorded data has not been run. There is a back-log of data building up and with the present computer installation,

it seems improbable that little more than half of the data can be processed as fast as it is taken. The computer situation should be greatly

improved during the summer or early next fall when a much faster computer is to be installed at the KBS-Boulder Laboratories.
-43-

7. REFERENCES

[1] P. A. Forsyth, E. L. Vogan, D. R. Hansen, and C. 0. Hines, "The

Principles of JANET - A Meteor-Burst Communications System," Proc.

IRE, vol. k-5, no. 12, pp. l6k2 - 1657, December, 1957.

[2] V. R. Eshleman, "On the Wavelength Dependence of the Information

Capacity of Meteor-Burst Propagation," Proc. IRE, vol. k^, no. 12,

pp. 1710 - 171^, December, 1957.

[3] W. R. Vincent, R. T. Wolfram, B. M. Sefford, W. E. Jaye, and A.

M. Peterson, "Analysis of Oblique Path Meteor-Propagation Data

from the Communications Viewpoint," Proc. IRE, vol. k^, no. 12,

pp. 1701 - 1707, December, 1957.

[k] Kenneth A. Norton, "System Loss in Radio Wave Propagation,"

Journal of Research, vol. 63D, no. 1, pp. 53-73* July-August, 1959«

[5] J. N. Gorham, A. M. Gray, and G. R. Sugar, unpublished report,

National Bureau of Standards, December, 1959«

[6] D. K. Bailey, R. Bateman, and R. C. Kirby, "Radio Transmission at

VHF by Scattering and Other Processes in the Lower Ionosphere,"

Proc. IRE, vol. ^3, no. 10, pp. Il8l - 1230, October, 1955.

[7] G. R. Sugar, "Some Fading Characteristics of Regular VHF

Ionospheric Propagation," Proc. IRE, vol. kj>, no. 10, pp. 1^32 -

1^-36, October, I955.

[8 J G. F. Montgomery and G. R. Sugar, "The Utility of Meteor Bursts

for Intermittent Radio Communication," Proc. IRE, vol. ^5, no. 12,

pp. 168^ - 1693, December, 1957.

U.S. DEPARTMENT OF COMMERCE

Frederick H. Mueller, Secretary

NATIONAL BUREAU OF STANDARDS

A. V. Astin, Director

THE NATIONAL BUREAU OF STANDARDS

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

Boulder, Colo., 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 field indicated by 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. Resistance and Reactance. Electrochemistry. Electrical Instruments. Magnetic Measurements.

Dielectrics. METROLOGY. Photometry and Colorimetry- Refractometry. Photographic Research. Length. Engineering

Metrology. Mass and Scale. Volumetry and Densimetry.

HEAT. Temperature Physics. Heat Measurements. Cryogenic Physics. Rheology. Molecular Kinetics. Free

Radicals Research. Equation of State. Statistical Physics. Molecular Spectroscopy.

RADIATION PHYSICS. X-Ray. Radioactivity. Radiation Theory. High Energy Radiation. Radiological

Equipment. Nucleonic Instrumentation. Neutron Physics.

CHEMISTRY. Surface Chemistry. Organic Chemistry. Analytical Chemistry. Inorganic Chemistry. Electrodeposition. Molecular Structure and Properties of Gases. Physical Chemistry. Thermochemistry. Spectrochemistry. Pure Substances. MECHANICS. Sound. Pressure and Vacuum. Fluid Mechanics. Engineering Mechanics. Combustion Controls. ORGANIC AND FIBROUS MATERIALS. Rubber. Textiles. Paper. Leather. Testing and Specifications.

Polymer Structure. Plastics. Dental Research.

METALLURGY. Thermal Metallurgy. Chemical Metallurgy. Mechanical Metallurgy. Corrosion. Metal Physics.

MINERAL PRODUCTS. Engineering Ceramics. Glass. Refractories. Enameled Metals. Constitution and

Microstructure.

BUILDING RESEARCH. Structural Engineering. Fire Research. Mechanical Systems. Organic Building Materials. Codes and Safety Standards. Heat Transfer. Inorganic Building Materials. APPLIED MATHEMATICS. Numerical Analysis. Computation. Statistical Engineering. Mathematical

Physics.

DATA PROCESSING SYSTEMS. Components and Techniques. Digital Circuitry. Digital Systems. Analog

Systems. Applications Engineering.

ATOMIC PHYSICS. Spectroscopy. Radiometry. Mass Spectrometry. Solid State Physics. Electron Physics.

Atomic Physics.

INSTRUMENTATION. Engineering Electronics. Electron Devices. Electronic Instrumentation. Mechanical

Instruments. Basic Instrumentation.

Office of Weights and Measures. BOULDER, COLO.

CRYOGENIC ENGINEERING. Cryogenic Equipment. Cryogenic Processes. Properties of Materials. Gas

Liquefaction.

IONOSPHERE RESEARCH AND PROPAGATION. Low Frequency and Very Low Frequency Research. Ion- osphere Research. Prediction Services. Sun-Earth Relationships. Field Engineering. Radio Warning Services. RADIO PROPAGATION ENGINEERING. Data Reduction Instrumentation. Radio Noise. Tropospheric Measurements. Tropospheric Analysis. Propagation-Terrain Effects. Radio-Meteorology. Lower Atmosphere Physics.

RADIO STANDARDS. High frequency Electrical Standards. Radio Broadcast Service. Radio and Microwave

Materials. Atomic Frequency and Time Standards. Electronic Calibration Center. Millimeter-Wave Research.

Microwave Circuit Standards.

RADIO SYSTEMS. High Frequency and Very High Frequency Research. Modulation Research. Antenna Research. Navigation Systems. Space Telecommunications.

UPPER ATMOSPHERE AND SPACE PHYSICS. Upper Atmosphere and Plasma Physics. Ionosphere and

Exosphere Scatter. Airglow and Aurora. Ionospheric Radio Astronomy.

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