ids

OCT l 9 195S

technical ^iot&

PB 151368

9fc.9

FREQUENCY DEPENDENCE OF

VHF IONOSPHERIC SCATTERING

by James C. Blair

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

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NATIONAL BUREAU OF STANDARDS

technical <7iote

No. 9

APRIL 1959

FREQUENCY DEPENDENCE OF VHF IONOSPHERIC SCATTERING

James C. Blair

The work described in this Report was carried out on behalf of the U. S. Air

Force, under support extended by Headquarters, Airways and Air Communications

Service, 1823rd AACS Group (now known as Detachment 1, Ground Electronics Engineering

Installation Agency) Andrews Air Force Base,

Maryland

.

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

CONTENTS

PAGE

1

.

INTRODUCTION 1

2EXPERIMENTAL FACILITIES 2

2 .1 Antennas 2

2.2 Transmitters 3

2 .

3

Receiving and Recording Equipment 3

3. FREQUENCY DEPENDENCE OF AVERAGE POWER k

3.1 Frequency Dependence Predicted by Theories k

3.2 Measured Values of Exponent k

3.3 The Influence of Meteor Bursts on the Received Signal... 5

3.^ Frequency Dependence of Signals from Sporadic E 8

3.5 SID Behavior 9

k. AMPLITUDE DISTRIBUTIONS AND FADING RATES 10

4.1 Amplitude Distributions 11

k.2 Fading Rates 11

5 . SUMMARY OF MEDIAN VALUES OF RECEIVED SIGNALS 12

6

.

DISCUSSION AND CONCLUSIONS 13

7. ACKNOWLEDGMENT lk

8

.

REFERENCES lk

9. LIST OF FIGURES 15

FREQUENCY DEPENDENCE OF VHF IONOSPHERIC SCATTERING

by

James C Blair

1 . INTRODUCTION

An accurate knowledge of frequency-dependence of scattered power

is not only of importance in the establishing of communication circuits,

but theoretical studies of previous data have pointed out that it is a vital parameter in basic understanding of the scattering mechanism.

2

Earlier experiments of frequency-dependence were limited to

observations of mean signal intensity at three frequencies, but only a pair simultaneously.

This report contains data obtained by recording received signal

intensities simultaneously at five frequencies over the 1295 km path

between the Long Branch transmitting station at Long Branch, Illinois,

and the receiving site at Boulder, Colorado (Table Mesa field station).

The data presented here cover the period of September 1, 1957 "to June 30 j 1958 (except for some later data on meteor bursts and sudden

Ionospheric disturbances). Good simultaneous signal intensity records

were obtained for most of this period on 30, kO, 50 and jk Mc. The

available transmitter at 108 Mc was not suitable for continuous reliable

records prior to June 5> 1958.

In addition to the routine, 2k hour-a-day recording of average

received power, a set of high-speed records was made for 10-minute

intervals at different times during one day and analyzed for amplitudedistribution and fading-rate. Also, a low-sensitivity recording was made for the study of meteor bursts.

Data presented here show the measured results of frequency dependence of average received power and illustrate how the level of

average received power is influenced by meteoric ionization, sporadic-E
- 2 - ionization, and ionospheric and magnetic disturbances. A summary of

hourly median and upper and lower decile values on all frequencies is

included, as well as data on amplitude distributions and fading rates.

2. EXPERIMENTAL FACILITIES

All signals recorded in obtaining the data presented here were

transmitted from the Long Branch Radio Propagation Transmitting Station

near Kilbourne, Illinois, and received at Boulder, Colorado. The re- corded signal intensities were adjusted to equivalent line losses and

transmitter powers. The geographical coordinates of the terminals are:

Long Branch field station k0° 13 Nj 90° 01 W

Boulder (Table Mesa field station) 1+0° 08 Nj 105° 15 W.

The path length is 1295 kilometers.

The frequencies used and the periods of operation are listed

below:

Frequency Period

30.00 Mc

30.005

1+0.00

1*0.006

1*0.88

I+9.60

1+9.61+

1+9.88

73-88

73-81+

107.80

Sept. 1, 1957 - Dec. 5, 1957

Dec. 5, 1957 - June 30, 1958

Sept. 1, 1957 - Dec. 5, 1957

Dec. 5, 1957 - May 1, 1958

May 1, 1958 - June 30, 1958

Sept. 1, 1957 - Nov. 21, 1957

Nov. 21, 1957 - Mar. 25, 1958

Mar. 25, I958 - June 30, I958

Sept. 1, 1957 - Oct. 18, 1957

Oct. 18, 1957 - June 30, 1958

Nov. 9, 1957 - Dec. 9, 1957

Mar. 26, 1958 - Apr. 5, 1958

May 29, 1958 - June 30, 1958

2.1 Antennas

In order to illuminate the scattering volume uniformly at all

frequencies, scaled rhombic antennas were used at both the transmitters

and receivers. This means that the dimensions and heights of the
- 3

- antennas were made proportional to the wave lengths of the signals

they transmitted and received. These rhombic antennas have a calculated

plane wave gain of approximately 20 db, relative to a dipole, with the

axis of the main lobes inclined at angles of k.6 degrees above the

horizon. The beam widths are approximately 6 to the half -power points

in the horizontal and vertical planes . The results given herein are presented prior to completion of actual calibrating measurements on

all antenna systems and are subject to some review after such measurements are available

2.2 Transmitters

Unmodulated continuous -wave signals were transmitted in all cases.

The transmitter powers for most of the transmission were as follows:

2 kilowatts at 30 Mc and kO Mc, 10 kilowatts at 50 Mc, 9 kilowatts at

Jk Mc, and k kilowatts on IO7.8 Mc . The limitations of available

transmitters of proper capacity made the logical arrangement of greater

power on higher frequencies impossible.

2.3 Receiving and Recording Equipment

In order to realize usable signal-to-noise ratios, receivers of

the double -conversion type were used to make narrow-bandwidth operation

possible. The 30, ^®> 50 and 7^ Mc signals were recorded with bandwidths of 300 cycles per second and the 108 Mc signals were recorded

with a bandwidth of 25 cycles per second. Receiver local oscillators

with a high degree of precision were employed to assure the receivers

were always properly tuned.

The continuous signal recordings were made on a one-milliampere

pen recorder at a recording speed of three inches per hour. The

amplitude -distribution and fading-rate data were recorded at a speed

of 50 millimeters per second on a high-speed pen recorder. Meteor

bursts were recorded at 10 millimeters per second.
- k - The receivers were calibrated once each day by substituting a standard signal generator for the antennas. The calibration of the

signal generator was checked by comparing its output with precise

standards, and the data were adjusted to compensate for the errors

found. A 6 db pad was inserted in the generator circuit to make the

generator read open-circuit antenna voltage.

3. FREQUENCY DEPENDENCE OF AVERAGE POWER

3.1 Frequency Dependence Predicted

by Theories

Earlier scattering theories have predicted that simultaneous

transmissions on different frequencies over the same path, with the

same antenna apertures and transmitter powers, will show that receiver

available power varies inversely as frequency raised by some exponent,

n. The Booker -Gorden scattering theory gives a value of k for n. k

Eckersley's scattering model indicates a value of 8. Later work by

1

Wheelon deals with the possibility that the exponent may be smaller

for frequencies between 30 to 50 Mc than it is for frequencies from

2 5 50 to 100 Mc, as earlier measurements indicated. Wheelon also deals

with the diurnal variations of the exponent.

3.2 Measured Values of Exponent

One important objective of this experiment has been to test these

theories and determine whether a single value of n is observed throughout the frequency range, or the nature of the curvature or cutoff of

such a power law. The data presented in figures 1 and 2 are plots of

the median values of signals that were received simultaneously on four

frequencies during March, 1958 • The relative median values of received

signal intensity are plotted for every hour of the day. Figures 3 and

k are similar plots of data obtained on five frequencies during June,

1958. The deviations of the points from straight lines of average

slope are small, which indicates that for any given time n is a constant

and can be determined quite precisely.
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- 5 - The average -slope lines drawn and the points plotted are those

from values obtained directly using scaled rhombic antennas. The

effective area of the receiving antennas -varies as the wave-length

squared; it is. necessary to make a corresponding adjustment of the

data if the frequency dependence is to be expressed on a per-unit or constant-with-frequency aperture basis. In figures 1 through k, n is

used to designate the value of the exponent using scaled antennas and

n to designate the value expressed on a per -unit -aperture basis. The

antenna-aperture adjustment lowers the value of the exponent by 2.

All values of signal intensity have been adjusted to the same transmitter power and equivalent line losses. Adjustments have been

made to eliminate errors in the calibration generators . The antennas

are assumed to have the same gains. Every possible attempt has been

made to eliminate signals influenced by sporadic E from the data.

The diurnal variation of the exponent n is shown in figure 5.

Curve E is for March and curve E. is for June. The lowest value of

m j n in March is 5.3 at 0600 hours,, while the highest is 7.9 at 1700

hours. The values for June are slightly lower than those for March

in the morning hours and are lower by an amount greater than 2 between

1700 and 1800 hours. There is a strong suggestion that the low midday

exponents in June are an example of the same effect found during SID

occurrences. At these times the high-frequency signal strength is

increased in relation to the low-frequency strength, which may even

decrease. This effect is described in Section 3-5 •

3-3 The Influence of Meteor Bursts on the

Received Signal

One effect of noticeable meteoric influence in the records is to

lower the frequency exponent n . In other words, an apparent result

contributed from meteor bursts is to raise the composite signal intensity disproportionately at the high frequencies compared to low

frequencies.
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22 23 00

RELATION OF METEORIC ACTIVITY TO CHANGES IN SIGNAL LEVEL AND EXPONENT VALUE
- 6 -

These tendencies can be discerned in figure 5, in which diurnal

curves of meteoric activity , composite signal level, and frequencyexponent are plotted on the same time scale . It is seen that the total

signal intensity (curve S.) is higher at all hours in June than in

J March (curve S ) . Both the March and June curves of signal intensity

have their minima between 1800 and 2100, an effect that seems to be

associated with the diurnal minimum of meteoric activity between these

hours

It should be pointed out that curves M . and M are curves of

m

meteor whistles and not bursts. However, these curves agree generally

in both diurnal and seasonal variations with data from radar obser7 vations taken with a nondirectional antenna . For this reason these

curves should represent a fair approximation to the variations of

meteor-burst activity.

Comparisons of the signal intensity and frequency exponent curves

for the two months of March and June suggest certain possible meteoric

effects . The increased meteoric activity in June compared with March

may be related to the uniformly higher values of signal intensity in

June, although this is only a conjecture. The diurnal curves of n in

March and June may be interpreted as reflecting both meteoric and solar

influences, with the solar influence predominating in the hours around

midday and the meteoric influence having control at other hours.

Both the 2_ and E curves maintain fairly low values from about

2100 in the evening until about 0600 the following morning. (Slightly

increased values of n are found between 0100 and 0^00, but the freo

' quency exponent is very low at 0600, about the time when meteoric

activity is at its diurnal maximum.) With increasing solar radiation

during the early morning the value of n increases gradually, at least

in March, even though meteoric activity is still high. This continues

until about noon. During the afternoon the value of n maintains a broad maximum in June, while in March it increases to relatively high
- 7

- values . In these hours there appears to take place a transition between

solar and meteoric control. The high values of n occur after the

o diurnal peak of solar activity has heen passed. It thus appears that

the low levels . of meteoric activity are responsible for the high values

of n in the late afternoon. Finally, by the time the S. and S curves

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reach their diurnal minimum the values of n have also declined to low

o values

.

It is of interest to note the correlation of the distance between

ordinates of curves S. and S with this distance between curves M. and

M . This shows clearly the effect of meteor -burst activity on average

signal intensity and suggests one means of separating the two components.

If curves such as S . and S are drawn for different frequencies, it

J m

may be possible to compare them with meteor activity curves and establish values of n for the composite scatter signal minus specularly

reflected meteor signal.

In order to obtain data on the frequency dependence of meteor

bursts that would not be significantly influenced by scatter signals,

a high-speed recording was made in the morning hours. Figure 6 shows

this recording that was made with low receiver sensitivity. Five

carrier frequencies were recorded simultaneously. The bursts are easy

to identify because they appear in time coincidence on all frequencies.

The stronger bursts usually have a saw-tooth shape on a decibel scale.

On a linear scale of antenna voltage vs. time, this would be an exponential curve with a very steep rise. As can be seen in the figure,

meteor bursts do not always have this ideal shape. But the customary

1 practice of measuring the duration at — times the peak value of

antenna voltage and calling this value of duration the time constant

of the meteor burst is followed here. Even though the bursts are easy

to identify, it is not possible to determine how much of the signal

rise is due to the meteor and how much is due to the scatter-signal

fading pattern on weak meteor bursts. Indeed, in some cases the

signal actually decreases on some frequencies during a burst. For
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- 8 - this reason, meteor bursts were included in the analysis only if they

exceeded the median value of the signal level by 20 db.

Figure 7 is a plot of the median peak values of 35 meteor bursts

at different carrier frequencies together with the median values of the

composite signal. The value of n for the meteor peaks is l.k compared

with k.2. for the composite signal. Figure 8 shows the time constant to

be about proportional to the 1.7 power of wave-length for this period.

It can be shown that the integrated power supplied by meteor bursts with

exponential decay is represented by a frequency exponent which is the sum of the frequency exponents applying to the time constant and the

peak power. If the exponent for peak power is added to the time-constant

exponent a value of 3*1 is obtained for the frequency dependence of received power during meteor bursts . This value is based on the assumption

of equivalent antenna apertures at different frequencies. It is to be

o compared with Eshleman's theoretical value, involving an exponent of

1.0 for meteor peak power adjusted for constant antenna aperture and an

exponent of 2.0 for meteor duration.

In conclusion, then, it appears that both meteoric activity and

solar activity exert a strong influence on the frequency exponent. Its

diurnal variation appears to arise from the changing resultant of these

two forces throughout the day.

3 A Frequency Dependence of Signals

from Sporadic E

As a means of separating sporadic E signals from scatter signals,

the following criteria were used to identify E signals: (l) signals

s must maintain a level of -60 db relative to inverse -distance values for

at least 1 minute on the carrier frequency of 30 Mc, (2) the signal

enhancement of 30 Mc must last 12 minutes, (3) any signal enhancements

(signals clearly above the background scatter signals) on the higher

frequencies that are in time coincidence with conditions of (l) and (2)

on 30 Mc are considered sporadic E signals . It should be realized that

this is a different criterion than has been used for other measurements

when these data are compared with other results

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30 40 50 FREQUENCY

70 100 200

AVERAGE DURATION OF 35 STRONG METEOR BURSTS OCCURRING

DURING PERIOD OF 0430 TO 0545 MST, SEPT. 12, 1958

FIGURE 8
- 9

- Figure 9 is a plot of the median values of eleven simultaneous

occurrences of E on four frequencies . The eleven values were the only

ones observed simultaneously between September 1, 1957 and June 30* 1958*

Due to criterion used, the lower value of E on 7^- Mc is necessarily

s too high because of contributions of scatter to its median value ; that

is, the average value of E was only about 5 db above the scatter signal.

The curve does, however, show that the effects of E dimish rapidly with

s frequency. Figure 10 shows the total duration of E during the period

s of September 1, 1957 to June 30, 1958.

3.5 SID Behavior

Figure 11 shows a set of records made during an SID on March 29,

1958* At about 1125 hours high absorption is seen on 30 Mc, but as the

frequency is increased, this absorption condition gradually changes to one of enhancement. A plot of values of signal intensities from these

records is shown in figure 12. These records were made, as usual, by

transmitting and receiving on rhombic antennas. For comparison with

these, a plot of signal intensities from records obtained by transmitting

and receiving on Yagi antennas (from another installation) is shown in

figure 13. It will be noticed here that absorption is present on all

frequencies, although it is much greater at the lower frequencies. A

possible explanation for this difference in behavior on antennas of

different beam widths is that the Yagi signals came from off path and

thus traveled a greater distance through the absorbing layer. Figures

1^ and 15 are plots of an SID that occurred July 19, 1958* Similar

behavior is observed here

Figure l6 is a plot of signals received during a magnetic disturbance. Notice the absorption on 30 Mc is extremely great. The ?,0 Mc

signal drops some 7 db below the value of the hO Mc signal and reaches

a value that is about equal to that of the 50 Mc signal. Rapid decrease

in absorption is noticed with increase in frequency with enhancement

starting at about 73 Mc and becoming significantly great at 108 Mc. It

is of considerable interest to note that these effects correlate with

the magnetic record made at Boulder, Colorado.
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- 10 - A comparison of signal "behavior during SID's (figures 12 and 1*0

with that during magnetic disturbance reveals a difference that may have

physical significance. In figures 12 and 1^ the signal goes into its

abnormal level in a relatively small time interval and recovers more

slowly. This is the usual pattern of signal behavior during SID's.

However, the magnetic disturbance shown in figure l6 displays just the

opposite signal variations . The signal goes into its abnormal level

relatively slowly and recovers in a much smaller period of time.

These effects are evidently extreme cases of general effects that

2 are present all the time . Bailey, Bateman and Kirby found correlations

showing that in the Arctic, general increases in HF absorption were

accompanied by stronger VHF scatter signals and that higher magnetic

K-indexes were related to stronger VHF signals

.

A study of these effects is of interest from a practical standpoint,

because it adds an element of attractiveness to scatter communications

in regions where HF blackouts are frequent. Such a study is also of

considerable interest from the standpoint of obtaining a basic understanding of the ionosphere. For example, one school of thought has been

that scatter signals are due primarily, if not entirely, to reflections

10

or scattering from many meteor trails . The foregoing relations between

magnetic activity and signal intensity would tend to discredit such a

theory.

This tendency of lower-frequency signals to show absorption at the same time enhancements occur with higher frequency signals may help to

explain the lower value of the frequency-dependence exponent during the

middle of the day in June.

k. AMPLITUDE DISTRIBUTIONS AND FADING RATES

Amplitude -distribution and fading-rate data are important in modulation studies and useful in separating the components of received signal

that are due to meteor bursts, scatter mechanisms and sporadic E. In

this report, data are presented that were taken from high-speed signal

intensity records during periods of OV3O - 0^39, 1150 - 1200, 1917 - 1925

MST on June 27, 1958 and 0000 - 0010 MST, June 28, 1958. All frequencies
- 11 - presented in each figure were recorded simultaneously.

U.l Amplitude Distributions

Amplitude distributions for the above periods are shown in figures

17 to 2k, plotted on two different coordinate systems. It will be noticed

that the distributions of the noon signals are very close to Rayleigh

distributions for all but very weak signals while plots of the signals

taken during the other periods are more nearly log-normal, as shown by

the tendency of the points to form a straight line on normal probability

coordinate systems. The reason for this change of shape of the distribution is very probably the effect of meteor bursts on the signal during

these weaker-signal periods. The set of Rayleigh distributions that

was obtained from signals not evidently perturbed by meteors is one of

three sets that have been obtained during strong-signal periods and is

9 11

in agreement with earlier work done by Sugar and later Koch

k.2 Fading Rates

Fading rates have been observed to vary over a wide range of values.

In cases where sporadic E does not effect the signal, the extreme value

may be as much as from O.3 to 1.0 cps on 30 Mc and from 1.0 to 2.0 cps

on 108 Mc. In cases of strong sporadic E signals the fading rates are much lower. Sporadic E fading rates of less than 0.10 cps were observed

on 30 Mc . Simultaneous recordings on both rhombic and Yagi antennas

reveal that fading rates of signals received on the Yagi antennas are much greater, in some cases 5 times as great.

Figure 25 shows the dependence of fading rate on frequency for

three ten-minute periods . The log of average fading rate is plotted

against the log of frequency in megacycles. The average-slope lines

indicate the values of the exponent n in the relation, fading rate Of , on the assumption that n is constant over the frequency range. The same value of n, 1.07, is found for the early morning and noontime periods.

A lower value of n, 0.7*+, applies to the midnight period (curve 3)- A

comparison of the fading rates with the curve of meteoric activity

(figure 5) fails to reveal a simple dependence between the two. It is

of interest to note that the deviations of the points on curve 1, for
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FIGURE 25
- 12 -

the noon period, are small compared to the other two curves . For this

reason, it may he that the assumption of a constant exponent is justifiable only in cases where the signal is not appreciably affected by

meteor bursts

5 . SUMMARY OF MEDIAN VALUES OF RECEIVED SIGNALS

Figures 26 to 35 are plots of the hourly median and upper and lower

decile values of signals received during the period of September, 1957

through June, 1958. The signal intensity values are based on opencircuit antenna voltages for antenna impedances of 50 ohms . It is well

known that scatter signals have their lowest values at the equinoxes and

highest values in the summer. However, the data in these figures together with the low exponents for June (figure 5) show that this seasonal

effect is frequency-dependent. The 30 Mc signal has much less of this

seasonal variation than does the 108 Mc signal. The effect of absorption

is one factor tending to hold the signal levels down on the lower frequencies. The data presented under "SID Behavior" suggests a correlation

between low-frequency absorption and high-frequency enhancement, and the

frequency dependence in the seasonal variation is just another evidence

of such a correlation.

The dotted lines on figures 26 to 35 represent the values of signal

intensity including the effects of any sporadic E propagation that

occurred. Sporadic E effects were greatest in July; they were considerable in October, December, April, May and June. Minor sporadic E effects

appear in the figures for September, November, January and February.

None at all are seen in March.

In nearly all cases, the curves of figures 26 to 35 reach a minimum

in the vicinity of 1900 hours MST. As was shown in figure 5* this is

the period of lowest meteor-burst activity.

Within a given month the general signal level may rise or fall by

several decibels. For this reason some of the curves in figures 26-35

that are based on only a few days ' data concentrated in a particular

part of the month do not represent the true median values for the month.

However, the straight-line frequency dependence relationship found to
DOTTED LINES REPRESENT SIGNAL INFLUENCED BY Es

DATA WERE OBTAINED FOR 15 OR MORE DAYS AT ALL HOURS J I I I I

DOTTED LINES REPRESENT SIGNAL INFLUENCED BY Es

DATA WERE OBTAINED FOR 20 OR MORE DAYS AT ALL HOURS J | | | |

105° W. TIME

DOTTED LINES REPRESENT SIGNAL INFLUENCED BY Es

DATA WERE OBTAINED FOR 26 OR MORE DAYS AT ALL HOURS J I I I I

DOTTED LINES REPRESENT SIGNAL INFLUENCED BY Es

73.88 Mc -

DATA WERE OBTAINED FOR 19 OR MORE DAYS AT ALL HOURS J I I I I

105° W TIME 105° W. TIME VALUES OF RECEIVED SIGNAL INTENSITY EQUALED OR EXCEEDED 10%, 50%, AND 90% OF THE TIME FOR THE MONTH OF SEPTEMBER, 1957. (ALL VALUES ADJUSTED TO 2 KILOWATTS TRANSMITTER POWER)

RECEIVED SIGNAL INTENSITY

FIGURE 26
DOTTED LINES REPRESENT SIGNAL INFLUENCED 8Y Es

DATA WERE OBTAINED FOR 27 OR MORE DAYS AT ALL HOURS J I I I I

DOTTED LINES REPRESENT SIGNAL INFLUENCED BY Es

DATA WERE OBTAINED FOR 12 OR MORE DAYS AT ALL HOURS J I I I I

DOTTED LINES REPRESENT SIGNAL INFLUENCED BY Es

105° W TIME 105" W. TIME VALUES OF RECEIVED SIGNAL INTENSITY EQUALED OR EXCEEDED 10%, 50%, AND 90% OF THE TIME

FOR THE MONTH OF OCTOBER, 1957. (ALL VALUES ADJUSTED TO 2 KILOWATTS TRANSMITTER POWER)

RECEIVED SIGNAL INTENSITY
DOTTED LINES REPRESENT SIGNAL INFLUENCED BY Es

DATA WERE OBTAINED FOR 29 OR MORE DAYS AT ALL HOURS

I I I I I

DATA WERE OBTAINED FOR 17 OR MORE DAYS AT ALL HOURS

I I I I I

49.6 Mc. _ l60

DATA WERE OBTAINED FOR 29 OR MORE DAYS AT ALL HOURS

I I I I L

DATA WERE OBTAINED FOR 25 OR MORE DAYS AT ALL HOURS

I

| I I

I

DATA WERE OBTAINED FOR 12 OR MORE DAYS AT ALL HOURS -40 I 1 1 1

VALUES OF RECEIVED SIGNAL INTENSITY EQUALED OR EXCEEDED

10%, 50%, AND 90% OF THE TIME FOR THE MONTH OF NOVEMBER, 1957. (VALUES ADJUSTED TO 2 Kw. TRANSMITTER POWER)

RECEIVED SIGNAL INTENSITY
OOTTED LINES REPRESENT INFLUENCED BY E s

. DATA WERE OBTAINED FOR 28 DAYS OR MORE AT ALL HOURS.

~l

A

DOTTED LINES REPRESENT SIGNAL "*0 Mc

INFLUENCED BY E s. DATA WERE OBTAINED FOR 23 OR MORE DAYS AT ALL HOURS.

105" W TIME 105° W TIME

DATA WERE OBTAINED FOR 22 OR MORE

DAYS AT ALL HOURS.

105° W. TIME 105° W TIME

DATA WERE OBTAINED FOR 7 OR MORE

DAYS AT ALL HOURS

VALUES OF RECEIVEO SIGNAL INTENSITY EQUALED OR EXCEEDED

10%, 50%, AND 90% OF THE TIME FOR THE MONTH OF DECEMBER 1957. (VALUES AOJUSTED TO 2 Kw TRANSMITTER POWER)

RECEIVED SIGNAL INTENSITY
DATA WERE OBTAINED FOR 30 OR MORE DAYS AT ALL HOURS J I

I I I

105° W TIME I05»W. TIME

DOTTEO LINES REPRESENT

INFLUENCED BY Es

DATA WERE OBTAINED FOR 30 OR MORE DAYS AT ALL HOURS J I I

DATA WERE OBTAINED FOR 22 OR MORE DAYS AT ALL HOURS J I I I I

I05°W TIME I05°W TIME

VALUES OF RECEIVED SIGNAL INTENSITY EQUALED OR EXCEEDED 10%, 50%, AND 90 % OF THE TIME FOR THE MONTH OF JANUARY, 1958. (ALL VALUES ADJUSTED TO 2 KILOWATTS TRANSMITTER POWER)

RECEIVED SIGNAL INTENSITY

FIGURE 30
DOTTED LINES REPRESENT SIGNAL INFLUENCED BY Es

DATA WERE OBTAINED FOR 27 OR MORE DAYS AT ALL HOURS J I I I 1

-

1 1 1 1 1 40.006 Mc

-

-

\ VlO % /

. V^ 50 %

< z^r x

DATA WERE OBTAINED FOR 28 \90 % ,r

DAYS AT ALL HOURS

1 1 1 1 1

105° W. TIME

1 1 1 1 1 /^ 1 49.64 Mc —

^ / / \ \

1°°*'/- / / \ >v 50%

"-^ -90%

DATA WERE OBTAINED FOR 27 OR MORE DAYS AT ALL HOURS

1 1 1 1 1

DATA WERE OBTAINED FOR 20 OR MORE DAYS AT ALL HOURS J I I

105 °W. TIME 105° W. TIME

VALUES OF RECEIVEO SIGNAL INTENSITY EQUALED OR EXCEEDED 10%, 50%, AND 90% OF THE TIME

FOR THE MONTH OF FEBRUARY, 1958. (ALL VALUES ADJUSTED TO 2 KILOWATT TRANSMITTER POWER)

RECEIVED SIGNAL INTENSITY
1 1 1 1 1

30.005 Mc. "

30 _

<n -

Xooin 20 * _

UJ>o

CD<

-O

T3

10 -

<^s. / J y v \ \ io%

' f \ \ 50 %

*" ^^ \. 90% -

DATA WERE OBTAINED FOR 29 OR MORE DAYS AT ALL HOURS

1 1 1 1 1

150 -

40.006 Mc. DATA WERE OBTAINED FOR 27 OR MORE DAYS AT ALL HOURS

105° W TIME

73.84 Mc. DATA WERE OBTAINED FOR 29 OR MORE DAYS AT ALL HOURS

DATA WERE OBTAINED FOR 25 OR MORE DAYS AT ALL HOURS

I I I

I

105" W. TIME 105° W TIME

-

I 1 1 1 1

107.8 Mc. —

/ /— , "\^V \ s 10% \^— y^ / \_~—S.50%^- ** ^ ' Nv

90%^'^ -

DATA WERE OBTAINED FOR 4 OR MORE DAYS AT ALL TIMES

1 1 1 1 1

VALUES OF RECEIVED SIGNAL INTENSITY EQUALED OR EXCEEDED

10%, 50%, AND 90% OF THE TIME FOR THE MONTH OF MARCH, 1958. (VALUES ADJUSTED TO 2 Kw TRANSMITTER POWER)

RECEIVED SIGNAL INTENSITY
.1 A/ t

\

DOTTED LINES REPRESENT

INFLUENCED BY E«. DATA WERE OBTAINED FOR 18 OR MORE DAYS AT ALL HOURS.

40.006 Mc

DATA WERE OBTAINED FOR 21 OR MORE DAYS AT ALL HOURS.

105° W TIME 105° W. TIME

OATA WERE OBTAINED FOR 19 OR MORE DAYS AT ALL HOURS

DATA WERE OBTAINED FOR 16 OR MORE DAYS

AT ALL HOURS

105° W. TIME 105° W. TIME

DATA WERE OBTAINED FOR 4 OR MORE DAYS

AT ALL HOURS.

VALUES OF RECEIVED SIGNAL INTENSITY EQUALED OR EXCEEDED

10%, 50%, AND 90% OF THE TIME FOR THE MONTH OF

APRIL 1958. (VALUES ADJUSTED TO 2 Kw TRANSMITTER POWER)

RECEIVED SIGNAL INTENSITY
DOTTED LINES REPRESENT] SIGNAL INFLUENCED

BY E»

105° W TIME

DOTTED LINES REPRESENT SIGNAL INFLUENCED BY Es

DATA WERE OBTAINED F( MORE DAYS AT ALL HOURS J I I

DOTTED LINES REPRESENT SIGNAL INFLUENCED BY Es

DATA WERE OBTAINED FOR 27 OR MORE DAYS AT ALL HOURS J I I L

s I05°W. TIME

12 105" W. TIME16

VALUES OF RECEIVED SIGNAL INTENSITY EQUALED OR EXCEEDED 10%, 50%, AND 90% OF THE TIME

FOR THE MONTH OF MAY, 1958 (ALL VALUES ADJUSTED TO 2 KILOWATTS TRANSMITTER POWER)

RECEIVED SIGNAL INTENSITY

FIGURE 34
DOTTED LINES REPRESENT

SIGNAL INFLUENCED BY Es

DATA WERE OBTAINED FOR 27 OR MORE DAYS AT ALL HOURS J I I I I

DATA WERE OBTAINED FOR 29 OR MORE OAYS AT ALL HOURS J I

I I I

105° W TIME 105° W. TIME

DATA WERE OBTAINED FOR 26 OR MORE DAYS AT ALL HOURS J I I I 1

i

i i ii73 84 Mc —

^-" >. \ 10 % ^y

/ ^~^ \ \^ >—_, ^0%.

' . \ Wk

III DATA WERE OBTAINED FOR 26 OR MORE DAYS AT ALL HOURS

105" W TIME

DATA WERE OBTAINED FOR 23 OR MORE DAYS AT ALL HOURS J I I I I

105" W TIME

VALUES OF RECEIVED SIGNAL INTENSITY EQUALED OR EXCEEDED

10%, 50%, 9ND 90% OF THE TIME FOR THE MONTH OF JUNE, 1958. (ALL VALUES ADJUSTED TO 2 Kw TRANSMITTER POWER)

RECEIVED SIGNAL INTENSITY

FIGURE 35
- 13 - hold in figures 1-k may be used to determine median values that more

nearly represent the month at any given hour. The median values of

signal on frequencies where large samples were obtained may he plotted

on semi -log coordinates (db vs. frequency) and a straight line drawn

through the points and the probable median values for other frequencies

may be read off the graph.

6. DISCUSSION AND CONCLUSIONS

The value of n may vary from about 6 to 8 during periods of strong

scatter signals and may reach values somewhat less than 5 during periods

of weak scatter signal and strong meteoric activity. Meteoric activity

is one powerful factor that influences these changes, but evidently is

not the only one . The value of n varies diurnally and from month to

month

Other important results of this study are summarized below:

1. Signal intensity changes during SID's differ in direction

according to the frequency of the signal.

2. Amplitude distributions are of a different type for periods

of relatively low and relatively high meteoric influence.

3. The value of n varies throughout the day in accordance with

the relative importance of meteoric and non-meteoric com- ponents of the signal.

k. The frequency-dependence analysis of signals from strong

meteor bursts gives low values of n . o

5. Magnetic disturbance was observed in one instance to produce

signal -intensity behavior similar to that characteristic of

SID's.

There is evidence from the SID data and from seasonal variations

in exponent that cases of high absorption at HF will tend to be

accompanied by abnormally high signals at VHF. 5 Mc recordings are now being made simultaneously with the other frequencies to test for

such a correlation.
- Ik -

7 . ACKNOWLEDGMENT

The observations and measurements reported herein were carried

out with the assistance of Messrs. R. P. Fitzpatrick, C. H. Johnson,

D. L. Ross and J. L. Green, Discussions with A. D. Wheelon and

K. L. Bowles have been helpful.

8 . REFERENCES

(1) Albert D. Wheelon, "Radio Frequency and Scattering Angle

Dependence of Ionospheric Scatter Propagation at VHF",

J. Geophys. Res., 62, 93 (1957)

(2) D. K. Bailey, R. Bateman, and R. C. Kirby, "Radio Transmission

at VHF by Scattering and other Processes in the Lower Ionosphere", Proc. I.R.E. k3, 1181 (1955)

(3) D. K. Bailey, R. Bateman, et al., "A New Kind of Radio

Propagation at Very High Frequencies Observable over Long

Distances", Phys . Res., 86, lUl (1952)

(k) T. L. Eckersley, "Studies in Radio Transmission", Jour. IEE

71, ^05 (1932)

(5) A. D. Wheelon, "Diurnal Variations of Signal Level and

Scattering Heights for VHF Propagation", J. Geophys. Res.,

62, 255 (1957)

(6) These data were taken from NBS Report 601^.

(7) L. A. Manning and V. R. Eshleman, "Meteors in the Ionopshere",

Proc. I.R.E. i£7, 186 (1959)

(8) V. R. Eshleman, "The mechanism of Radio Reflections from Meteoric

Ionization", Technical Report No. k^ } Electronic Research Lab,

Stanford Univ., Stanford, Calif., July 1952

(9) G. R. Sugar, "Some Fading Characteristics of Regular VHF

Ionospheric Propagation", Proc. I.R.E. k3, 1^32 (1955)

(10) D. W. R. McKinley, "Dependence of Integrated Duration of Meteor

Echoes on Wavelength and Sensitivity", Can. Jour. Phys., 32,

1*50 (195*0

(11) J. W. Koch, "Factors Affecting Modulation Techniques for VHF

Scatter Systems", to be published in Vol. CS-7, No. 2, I.R.E.

Transactions on Communications Systems
- 15 -

9- LIST OF FIGURES

Fig- 1 Dependence of Signal Intensity on Frequency for 15 Days

of March (00 - 12 hours).

Fig. 2 Dependence of Signal Intensity on Frequency for 15 Days

of March (12 - 00 hours).

Fig. 3 Dependence of Signal Intensity on Frequency for 10 Days

of June (00 - l6 hours).

Fig. k Dependence of Signal Intensity on Frequency for 10 Days

of June (16 - 22 hours).

Fig. 5 Relation of Meteoric Activity to Changes in Signal Level

and Exponent Value

.

Fig. 6 Simultaneous High-Speed Recordings of Meteor Bursts.

Fig. 7 Frequency Dependence of Peak Values of Strong Meteor Bursts

Compared with Frequency Dependence of the Composite Signal.

Fig. 8 Average Duration of 35 Strong Meteor Bursts.

Fig. 9 Median Values of Received Signal Intensities During Eleven

Simultaneous Occurrences of Sporadic E on Four Frequencies.

Fig. 10 Number of Hours Sporadic E Occurred from September, 1957

Through June, 1958.

Fig. 11 Records Made During an SID on March 29 > 1958

Fig. 12 Signal Behavior During SID of March 29, 1958 (Observed on Rhombic Antennas).

Fig. 13 Signal Behavior During SID of March 29, 1958 (Observed on Yagi antennas).

Fig. ik Signal Behavior During SID of July 19, 1958 (Observed on Rhombic Antennas).

Fig. 15 Signal Behavior During SID of July 19, 1958 (Observed on Yagi Antennas).

Fig. l6 Correlation of Magnetic Activity with Signal Behavior for

a Magnetic Disturbance Occurring July 8, 1958.
- 16 -

Fig. 17 Amplitude Distribution of Signal Intensity Values Received

During Period of 0^30 - 0*1-39 hours on June 27, 1958 (Normal

Coordinate System)

Fig. 18 Amplitude Distribution of Signal Intensity Values Received

During Period of 0^-30 - 0^39 hours, June 27, 1958 (Rayleigh

Coordinate System)

Fig. 19 Amplitude Distribution of Signal Intensity Values Received

During Period of 1150 - 1200 hours, July 27, 1958 (Normal

Coordinate System)

Fig. 20 Amplitude Distribution of Signal. Intensity Values Received

During Period of 1150 - 1200 hours, July 27, 1958 (Rayleigh

Coordinate System)

Fig. 21 Amplitude Distribution of Signal Intensity Values Received

During Period of 1917 - 1925 hours, July 27, 1958 (Normal

Coordinate System)

Fig. 22 Amplitude Distribution of Signal Intensity Values Received

During Period of 1917 - 1925 hours, July 27, I958 (Rayleigh

Coordinate System)

Fig. 23 Amplitude Distribution of Signal Intensity Values Received

During Period of 0000 - 0010 hours, June 28, 1958 (Normal

Coordinate System)

Fig. 2k Amplitude Distribution of Signal Intensity Values Received

During Period of 0000 - 0010 hours, June 28, I958 (Rayleigh

Coordinate System)

Fig. 25 Fading Rate vs Frequency From Records Made June 27 - 28,

1958.

Fig. 26 Values of Received Signal Intensity Equaled or Exceeded 10$,/

50$ and 90$ of the Time for September, 1957-

Fig. 27 Values of Received Signal Intensity Equaled or Exceeded 10$,

50$ and 90$ of the Time for October, 1957-

Fig. 28 Values of Received Signal Intensity Equaled or Exceeded 10$,

50$ and 90$ of the Time for November, 1957-

Fig. 29 Values of Received Signal Intensity Equaled or Exceeded 10$,

50$ and 90$ of the Time for December, 1957-
- 17 -

Fig. 30 Values of Received Signal Intensity Equaled or Exceeded 10$,

50$ and 90$ of the Time for January, 1958.

Fig. 31 Values of Received Signal Intensity Equaled or Exceeded 10$,

50$ and 90$ of the Time for February, I958.

Fig. 32 Values of Received Signal Intensity Equaled or Exceeded 10$,

50$ and 90$ of the Time for March, 1958.

Fig- 33 Values of Received Signal Intensity Equaled or Exceeded 10$,

50$ and 90$ of the Time for April, 1958.

Fig. 3^ Values of Received Signal Intensity Equaled or Exceeded 10$,

$ and 90$ of the Time for May, 1958.

Fig. 35 Values of Received Signal Intensity Equaled or Exceeded 10$

$ and 90$ of the Time for June, 1958.
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