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FREQUENCY DEPENDENCE OFVHF IONOSPHERIC SCATTERING
by James C. Blair
U. S. DEPARTMENT OF COMMERCENATIONAL 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 andmaintenance 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 pub-
lished 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.
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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 <7iote
No. 9
APRIL 1959
FREQUENCY DEPENDENCE OF VHF IONOSPHERIC SCATTERING
James C. Blair
The work described in this Report wascarried out on behalf of the U. S. AirForce, under support extended by Head-quarters, Airways and Air CommunicationsService, 1823rd AACS Group (now known asDetachment 1, Ground Electronics EngineeringInstallation Agency) Andrews Air Force Base,Maryland
.
NBS Technical Notes are designed to supplement the Bu-reau'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. Depart-ment 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
2
.
EXPERIMENTAL 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 amplitude-
distribution 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 de-
pendence 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:
PeriodFrequency
30.00 Mc30.005
1+0.00
1*0.006
1*0.88
I+9.60
1+9.61+
1+9.88
73-8873-81+
107.80
Sept. 1, 1957 - Dec. 5, 1957Dec. 5, 1957 - June 30, 1958
Sept. 1, 1957 - Dec. 5, 1957Dec. 5, 1957 - May 1, 1958May 1, 1958 - June 30, 1958
Sept. 1, 1957 - Nov. 21, 1957Nov. 21, 1957 - Mar. 25, 1958Mar. 25, I958 - June 30, I958
Sept. 1, 1957 - Oct. 18, 1957Oct. 18, 1957 - June 30, 1958
Nov. 9, 1957 - Dec. 9, 1957Mar. 26, 1958 - Apr. 5, 1958May 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 measure-
ments 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 band-
widths 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 Predictedby 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 by1
Wheelon deals with the possibility that the exponent may be smaller
for frequencies between 30 to 50 Mc than it is for frequencies from2 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 through-
out 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 ofm 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 theReceived 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 inten-
sity disproportionately at the high frequencies compared to low
frequencies.
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1 [ 1 1 1 1 1 1 1 1 1 1 1 I 1 1 1 1 1 1 1 1 1
- O BASED ON 4 FREQUENCIES _ ^- , EXPONENT - MARCH, 1958 -X BASED ON 5 FREQUENCIES >3^^Q>SX.
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49 88 Mc BOULDER -LONG BRANCH PATH 49.88 Mc BOULDER- LONG BRANCH PATH
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- / \ STERLING -CEDAR RAPIDS PATH _
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00 01 02 03 04 05 06 07 08 09 10 II 12 13 14 15 16 17 18 19 20 21
LOCAL TIME AT PATH MIDPOINT22 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 frequency-
exponent 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 inJ
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 ofm
meteor whistles and not bursts. However, these curves agree generally
in both diurnal and seasonal variations with data from radar obser-7vations 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 fre-o '
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 theo
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 curveso '
j mreach 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, itJ m
may be possible to compare them with meteor activity curves and estab-
lish 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 ex-
ponential curve with a very steep rise. As can be seen in the figure,
meteor bursts do not always have this ideal shape. But the customary1
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 re-
ceived power during meteor bursts . This value is based on the assumption
of equivalent antenna apertures at different frequencies. It is to beo
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.
3A Frequency Dependence of Signalsfrom Sporadic E
As a means of separating sporadic E signals from scatter signals,
the following criteria were used to identify E signals: (l) signalss
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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DURATION WAS MEASURED AT I /€ TIMESPEAK AMPLITUDE OF OPEN-CIRCUITANTENNA VOLTAGE.
30 40 50
FREQUENCY70 100 200
AVERAGE DURATION OF 35 STRONG METEOR BURSTS OCCURRINGDURING 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 necessarilys
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 withs
frequency. Figure 10 shows the total duration of E during the periods
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 dis-
turbance. 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 that2
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 under-
standing of the ionosphere. For example, one school of thought has been
that scatter signals are due primarily, if not entirely, to reflections10
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 modu-
lation 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 distri-
bution 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 11in 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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FREQUENCY, Mc/s
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FADING RATE vs. FREQUENCY FROM RECORDS MADE JUNE 27-28, 1958
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 justi-
fiable 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 open-
circuit 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 to-
gether 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 fre-
quencies. 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 consider-
able 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 SIGNALINFLUENCED 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 SIGNALINFLUENCED 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 TIMEFOR THE MONTH OF SEPTEMBER, 1957. (ALL VALUES ADJUSTED TO 2 KILOWATTS TRANSMITTER POWER)
RECEIVED SIGNAL INTENSITY
FIGURE 26
DOTTED LINES REPRESENT SIGNALINFLUENCED 8Y Es
DATA WERE OBTAINED FOR 27 OR MORE DAYS AT ALL HOURS
J I I I I
DOTTED LINES REPRESENT SIGNALINFLUENCED BY Es
DATA WERE OBTAINED FOR 12 OR MORE DAYS AT ALL HOURS
J I I I I
DOTTED LINES REPRESENT SIGNALINFLUENCED BY Es
105° W TIME 105" W. TIME
VALUES OF RECEIVED SIGNAL INTENSITY EQUALED OR EXCEEDED 10%, 50%, AND 90% OF THE TIMEFOR 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 HOURSI 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 REPRESENTINFLUENCED BY E s .
DATA WERE OBTAINED FOR 28 DAYSOR MORE AT ALL HOURS.
~l
A
DOTTED LINES REPRESENT SIGNAL "*0 McINFLUENCED 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 MOREDAYS AT ALL HOURS.
105° W. TIME 105° W TIME
DATA WERE OBTAINED FOR 7 OR MOREDAYS AT ALL HOURS
VALUES OF RECEIVEO SIGNAL INTENSITY EQUALED OR EXCEEDED10%, 50%, AND 90% OF THE TIME FOR THE MONTH OFDECEMBER 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 REPRESENTINFLUENCED 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 TIMEFOR 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 xDATA WERE OBTAINED FOR 28 \90 % ,r
DAYS AT ALL HOURS1 1 1 1 1
105° W. TIME
1 1 1 1 1
/ ^1 49.64 Mc
—
^ / / \ \ 1°°*'/-
/ / \ >v50%
"-^ -90%
DATA WERE OBTAINED FOR 27 OR MORE DAYS AT ALL HOURS
1 1 1 1 1
DATA WERE OBTAINED FOR 20 ORMORE 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>oCD<
-OT3
10 -
<^s. / J y v \ \ io%
'f \ \ 50 %
*" ^^ \. 90%
-
DATA WERE OBTAINED FOR 29 OR MORE DAYS AT ALL HOURS1 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%^- **
^ ' Nv90%^'^ -
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 REPRESENTINFLUENCED BY E«.
DATA WERE OBTAINED FOR 18 ORMORE 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 DAYSAT 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 DAYSAT 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 Ls
I05°W. TIME
12
105" W. TIME16
VALUES OF RECEIVED SIGNAL INTENSITY EQUALED OR EXCEEDED 10%, 50%, AND 90% OF THE TIMEFOR THE MONTH OF MAY, 1958 (ALL VALUES ADJUSTED TO 2 KILOWATTS TRANSMITTER POWER)
RECEIVED SIGNAL INTENSITY
FIGURE 34
DOTTED LINES
REPRESENTSIGNAL 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
ii i
ii73 84 Mc
—
^-" >. \ 10 %
^y/ ^~^ \ \^ >—_, ^0%.
'
. \ Wk
DATA WERE OBTAINED FOR 26 OR MORE DAYS AT ALL HOURSIII105" 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 AngleDependence of Ionospheric Scatter Propagation at VHF",J. Geophys. Res., 62, 93 (1957)
(2) D. K. Bailey, R. Bateman, and R. C. Kirby, "Radio Transmissionat VHF by Scattering and other Processes in the Lower Iono-sphere", Proc. I.R.E. k3, 1181 (1955)
(3) D. K. Bailey, R. Bateman, et al., "A New Kind of RadioPropagation at Very High Frequencies Observable over LongDistances", 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 andScattering 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 MeteoricIonization", Technical Report No. k^ } Electronic Research Lab,Stanford Univ., Stanford, Calif., July 1952
(9) G. R. Sugar, "Some Fading Characteristics of Regular VHFIonospheric Propagation", Proc. I.R.E. k3, 1^32 (1955)
(10) D. W. R. McKinley, "Dependence of Integrated Duration of MeteorEchoes on Wavelength and Sensitivity", Can. Jour. Phys., 32,1*50 (195*0
(11) J. W. Koch, "Factors Affecting Modulation Techniques for VHFScatter 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 Daysof March (00 - 12 hours).
Fig. 2 Dependence of Signal Intensity on Frequency for 15 Daysof March (12 - 00 hours).
Fig. 3 Dependence of Signal Intensity on Frequency for 10 Daysof June (00 - l6 hours).
Fig. k Dependence of Signal Intensity on Frequency for 10 Daysof June (16 - 22 hours).
Fig. 5 Relation of Meteoric Activity to Changes in Signal Leveland Exponent Value
.
Fig. 6 Simultaneous High-Speed Recordings of Meteor Bursts.
Fig. 7 Frequency Dependence of Peak Values of Strong Meteor BurstsCompared 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 ElevenSimultaneous Occurrences of Sporadic E on Four Frequencies.
Fig. 10 Number of Hours Sporadic E Occurred from September, 1957Through 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 onYagi Antennas).
Fig. l6 Correlation of Magnetic Activity with Signal Behavior fora Magnetic Disturbance Occurring July 8, 1958.
- 16 -
Fig. 17 Amplitude Distribution of Signal Intensity Values ReceivedDuring Period of 0^30 - 0*1-39 hours on June 27, 1958 (NormalCoordinate System)
.
Fig. 18 Amplitude Distribution of Signal Intensity Values ReceivedDuring Period of 0^-30 - 0^39 hours, June 27, 1958 (RayleighCoordinate System)
.
Fig. 19 Amplitude Distribution of Signal Intensity Values ReceivedDuring Period of 1150 - 1200 hours, July 27, 1958 (NormalCoordinate System)
.
Fig. 20 Amplitude Distribution of Signal. Intensity Values ReceivedDuring Period of 1150 - 1200 hours, July 27, 1958 (RayleighCoordinate System)
.
Fig. 21 Amplitude Distribution of Signal Intensity Values ReceivedDuring Period of 1917 - 1925 hours, July 27, 1958 (NormalCoordinate System)
.
Fig. 22 Amplitude Distribution of Signal Intensity Values ReceivedDuring Period of 1917 - 1925 hours, July 27, I958 (RayleighCoordinate System)
.
Fig. 23 Amplitude Distribution of Signal Intensity Values ReceivedDuring Period of 0000 - 0010 hours, June 28, 1958 (NormalCoordinate System)
.
Fig. 2k Amplitude Distribution of Signal Intensity Values ReceivedDuring Period of 0000 - 0010 hours, June 28, I958 (RayleighCoordinate 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.
U.S. DEPARTMENT OF COMMERCEFrederick H. Mueller, Secretary
NATIONAL BUREAU OF STANDARDSA. V. Astin, Director
THE NATIONAL BUREAU OF STANDARDS
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