August 1967 QST
Table of Contents
Wax nostalgic about and learn from the history of early electronics. See articles
QST, published December 1915 - present. All copyrights hereby acknowledged.
NASA (and its predecessor NACA),
and private and public operators have been monitoring solar
events in the optical realm for many decades while attempting
to correlate terrestrial phenomena with it. Auroral light displays
in the extreme polar regions have long been known to be caused
by solar flare and coronal mass ejections (CME). With the advent
of radio, the electrical nature of the upper atmosphere became
evident when static (AM) and long range propagation affected
long range communications. Extreme CME activity eventually was
associated with behavior of the electrical power grid; indeed,
massive blackouts and brownouts are to blame for many. Last
but not least came concern for sun-sourced electrons regarding
satellites. More than one 'bird' has been smoked by the sun's
November, on Thanksgiving Day, actually, comet
ISON, which could produce the most spectacular astronomical
display in our lifetime ("the comet of the century"), might
actually impact the sun. Depending on where it strikes (if it
strikes), some of the most violent solar electrons ever could
be hurdled toward the earth. The effects cannot be predicted;
we'll all find out real-time what our fate is. You might want
to make sure all your electronics devices have a full charge,
just in case. Update: It crashed into the sun.
432-Mc. Solar Patrol
A Study of Solar Noise in Relation to Radio Propagation
By Paul M, Wilson, W4HHK/A4HHK
In the spring of 1966, the "big dish" at W4HHK was comparatively
idle. Oscar IV was silent, moonbounce activity on 432 Mc. was
nil, and there were no troposcatter schedules in prospect. Then
an item in Sky and Telescope caught my eye. It told how NASA
planned to maintain a solar flare patrol as part of the space
program. Why not a solar patrol on 432 Mc.?
This seemed like a worthwhile effort. Though the flux density
of radio noise from the sun is measured daily by observatories,
their records are not immediately available to the amateur.
Our project would be a means of keeping track of solar activity
on a day-to-day basis. In addition it would be a way to evaluate
the antenna and receiving. system, and periodically check it.
Until now only an occasional "look" at the sun had been made.
Observation had been inconvenient because each session meant
trips up and down the tower to release and stow the dish. By
the middle of April, 1966, several events had made daily observations
feasible. A stowing device was built that permitted operation
from the ground. A commercial step attenuator was obtained for
calibrating solar noise recordings accurately. Last but not
least, a 432-Mc. preamplifier built with low-noise kMc. transistors
made a noticeable improvement in 432-Mc. receiver performance.
At this point it is desirable to examine the source of the
noise to be observed and measured. The sun is some 92 million
miles from earth, or 8.3 minutes of travel at the speed of light
and radio emissions. It is not a true point source, but for
most amateur purposes can be considered as one. According to
Bray and Kirchner,1 it can be represented as a ring
of about one degree angular diameter on the outside, and about
one-half degree on the inside. The sun is a source of noise
on radio frequencies, caused by plasma oscillations and gyro-oscillations
in the solar atmosphere, as well as noise originating in random
collision of electrons. Noise from the quiet sun is of the latter
type.2 A solar noise recording made when the sun
was relatively quiet is shown in Fig.1.
Fig. 1 - Noise of the sun on a relatively-quiet
day, Dec. 1, 1966. Noise was running between 3 and 3.5 db. American
sunspot count was 32. A 1-db. calibration dip is seen near the
center of the recording. A burst of ignition noise is seen at
Noise from a quiet sun appears to have random polarization,
but bursts of high intensity at 432 Mc. are elliptically to
linearly polarized.3 Sunspot activity of the current
11-year cycle (Cycle 20) is expected to peak some time in 1968.
The quiet sun looks like an approximate 500,000-degree Kelvin
source, rising to about 1,000,000 degrees K. when disturbed."
The amplitude of solar emission may remain relatively constant
for long periods, and then will be greatly enhanced during a
"noise storm." Such storms are often associated with solar flares
and certain geophysical disturbances, and may last for hours
Solar flares are sometimes, but not always, followed by aurora
some 20 to 40 hours later. The rotation period of the sun is
about 27 days, and there is a tendency for aurora to recur at
this rate. Some sunspots may survive several rotations before
disappearing. In a 1951 QST article,6 Moore pointed
out that correlation between sunspot number and aurora is not
as great as one might expect. But what about solar noise and
aurora, or sporadic E, F2 or transequatorial v.h.f.
propagation? It was hoped that regular solar noise observation
might serve as an indicator of propagation conditions, and possibly
give advance warning of events such as major auroras.
Besides helping you to keep up to date on what the sun is doing,
regular solar noise measurements are a means of evaluating system
performance, from antenna to receiver output. For given antenna
size, feed line loss and receiver temperature (or noise figure)
a certain minimum amount of solar noise should always be obtainable.
WIFZJ described how a 17-foot parabola and a receiver-feed line
combination with a 751-degrees Kelvin temperature would observe
a 3-db. increase in noise when aimed at the quiet sun.7
Another reference gives the quiet-sun noise level at 432 Mc.
as 21 db. below the receiver noise level when using a perfect
receiver and a dipole antenna. An increase of 10 db. could be
expected from an active sun.8
At the outset several questions were raised. Was the writer's
dish performing up to specifications? What short-term variations
would be observed? Could solar noise be used for reasonably
accurate comparisons of equipment? Text books on hand didn't
have all the answers. Thus one goal of the project was to resolve
some of these questions.
The Noise-Observing Setup
The equipment used for solar noise measurement at W4HHK is
shown in block-diagram form in Fig. 2. It doesn't have the simplicity
of visual devices such as the Aurorascope9 for checking
sunspot activity, but it does work, rain or shine. The antenna
is an 18-foot parabola, with a focal length of 90 inches, and
a diameter-to-focal-length ratio of 2.45. The slide-rule specifications
for 432 Mc. are 26 db. gain over isotropic, and a beam-width
of 9 degrees at the half-power points. It was made by the D.
S. Kennedy Company, and obtained through the Army MARS program.
The center is 35 feet above ground, at a 380-foot elevation.
Geographic location is latitude 35 02 48 North and longitude
89 40 04 West. The dish is fully steerable in azimuth and elevation
by an SCR-584 pedestal.
Fig. 2 - Block diagram of the 432-Mc. solar-noise
measuring setup at W4HHK.
A modified FPS-3 radar platform supports the pedestal and
dish. Selsyn indicators at the control point show the azimuth
and elevation in one-degree intervals. Steering is done by applying
d.c. power to the 1/2-h.p. pedestal motors.
The feed for the dish is a horizontal folded dipole, with
a plane reflector 16 inches in diameter. An air-dielectric balun
mounted at the feed matches 50-ohm coax to the balanced 300-ohm
dipole. A 38-foot length of foam RG-8 connects the balun to
a 60-foot run of 7/8-inch Heliax, from the base of the pedestal
to the shack. Overall line loss is about 2.25 db., according
to published figures.
Since the antenna is also used for transmitting, a coaxial
relay, not shown, is employed for transmit-receive switching.
It is worth mentioning that after several months of operating
a kilowatt transmitter alongside, no measurable change in receiver
noise figure has been observed. The feed line is disconnected
manually when the equipment is not in use, as a precaution against
damage from lightning and heavy static.
Each r.f. stage is in a separate aluminum box, with power
supplied by individual 9-volt batteries. The first r.f. amplifier
uses a KMC n.p.n. experimental transistor, with a factory-measured
noise figure of 2.8 db. (for the transistor). The second uses
a TIXMO5 p.n.p. transistor. Gain per stage is about 9 db. Each
has the common-emitter configuration, and is unneutralized.
Both are stable, even in the absence of input load. Both have
double-tuned input circuits, to minimize response to out-of-band
signals. In-band signals are not a problem, as the nearest 432-Mc.
station is 70 miles distant! The second r.f. stage feeds a 1N21F
mixer, which works into a 50-Mc. converter at 49.5 Mc., converting
again to 7 Mc., and followed by a 75A3 receiver and chart recorder.
The converter and 75A3 are always kept on standby when not in
use, to minimize trouble. The r.f. amplifiers and 432-Mc. converter
were built by the writer.
A constant-voltage line transformer was found to be necessary
to maintain reasonably good gain stability. Without it a recording
of a constant-amplitude signal would vary considerably, especially
during lengthy recordings. Apparently the main cause of this
was heater-voltage change, as the converter plate voltages are
all regulated. The converter seemed more sensitive to line-voltage
change than did the 75A3. This and other problems were ironed
out before regular observations began on June 1, 1966.
A 20-db. fixed pad is used at the converter output and a
10-db. fixed pad at the receiver input, with the step attenuator
in the 50-ohm line between them. This was done to insure operation
of the attenuator at its design impedance. The 75A3 mode switch
was modified to permit reception with the b.f.o. and a.v.c.
off. The receiver 500-ohm output is connected to a bridge rectifier,
which drives the Esterline-Angus 1-ma. strip-chart recorder.
Rectifier output is not linear, crowding at the low-signal end
of the scale. Esterline-Angus chart paper, type 132020, that
closely matches the rectifier response, was obtained surplus.
A chart speed of 3 inches per minute has been found a good compromise
between easily-read recordings and paper conservation. For long-duration
recordings a speed of 3 inches per hour has been used.
Radio observatories measure the flux density of solar radio
emissions by using the unit of 10-22 watts per square meter
per cycle per second. The method used by the writer measures
the ratio of solar noise to quiet-sky (background) noise in
decibels. The results of a typical measurement, made as described
below, are shown in Fig. 3. The feed line is connected to the
first r.f. amplifier and power is applied to both r.f. stages.
Converter crystal mixer current is adjusted to read 0.5 ma.
The 75A3 S-meter is observed to verify that two S-units of converter
noise is read with the receiver in the a.m. mode. The 75A3 a.v.c.
and b.f.o. are turned off, and the a.m. and c.w. limiters are
disabled. Audio gain is advanced to 75 percent of full volume,
and the" r.f." gain is reduced until the chart recorder reads
about one-third scale, as seen at the right edge of the recording.
Fig. 3 - Solar noise level of 5 db. recorded
March 3, 1967. Read chart from right to left. A chart speed
of 3 inches per hour was used at the start, as the dish was
centered on the sun for the recording in the upper right corner
of the chart, then changed to 3 inches per minute for the measurement.
Next come three levels of attenuation, inserted for calibration,
and another 15 seconds of solar noise. The dish is then turned
away from the sun, and the quiet-sky noise is recorded. A 50-ohm
termination is then substituted, giving about 0.5 db. more noise
than the quiet sky.
The dish is then steered toward the sun, and the azimuth
and elevation controls are adjusted until maximum noise is indicated
on the recorder. Audio gain is readjusted for a meter reading
of about 0.9 ma. Chart speed is shifted from the 3 inches per
hour, used while steering, to 3 inches per minute, and solar
noise is recorded for about 30 seconds. This is the first 5-db.
peak at the right. At this point several steps of attenuation
are inserted to calibrate the chart, usually beginning with
the 3-db. step. Normally the 3-, 4-, and 5-db. steps are each
recorded for 15 to 30 seconds, depending on the undesired responses
that may be present, such as from ignition or radar. In this
instance steps of 4, 5 and 6 db. were used. The audio is monitored
on a speaker, and the chart trace is observed, to make certain
that interference is not spoiling calibration and reception
Following the last level of calibration the attenuator is
switched out of the circuit, and full solar noise is again recorded
on the chart. If nothing has changed (dish heading by wind gust,
solar noise level, etc.) the reading will be about the same
as at the start. Though the sun is not tracked during the measurement,
the noise amplitude should remain constant, because of the antenna
beamwidth and the shortness of the measurement period.
The dish is then steered away from the sun to a point in
the northwest sky, the quietest heading for this location. Quiet-sky
noise level is recorded for 30 seconds to a minute, again making
certain that unwanted noise does not obscure the quiet-sky noise
level. As each measurement is being made the GMT date-time,
calibration steps, and other information are noted quickly on
the moving chart. Three to six measurements are made each day
in this manner, the entire operation taking 30 minutes or so.
More measurements are made if conditions warrant. Recordings
are examined at the end of the session, or later, and solar
noise readings determined. Periodically the noise of a 50-ohm
termination at the receiver input is recorded, in addition to
quiet-sky noise, to confirm receiver performance. Termination
noise is usually about 0.5 db. higher than quiet-sky noise,
as seen at the left edge of Fig. 3.
All readings are entered in the solar noise log, and the
section of chart with the highest reading is mounted and filed.
The highest reading is of particular interest because it shows
maximum solar activity during the observing period, and because
it is usually the most accurate. Any errors caused by steering,
noise, and equipment failure tend to degrade readings.
A solar noise recording made while the sun moved across the
dish is shown in Fig. 4. This was obtained by pointing the dish
at a point in the sky where the sun would be at a later time.
The Greenwich hour angle and declination of the sun were determined
from the Nautical Almanac.10 This information was
converted to azimuth and elevation by tables found in a Hydrographic
Office publication. 11 Receiver gain was adjusted
so that background noise deflected the recording pen about one-third
scale, and the chart speed set for 3 inches per hour. Recording
was started about an hour in advance of the time for which the
dish was positioned. When the sun came into view the solar noise
rose from the background level, peaked, and then slowly fell.
Insertion of suitable levels of attenuation, in this instance
4 and 5 db., provide a check on the performance and establish
the accuracy of the recording. Only the main lobe is seen at
present levels of solar activity. Minor lobes of the antenna
are too far down to show.
Fig. 4 - Movement of the sun across the dish
is shown in this 3-hour recording made with slow chart speed.
The antenna was aimed at a point where the sun would be later,
and left there to record the rise in noise level as the sun
passes. Calibrations of 4 and 5 db. inserted at the noise peak
show the strength of the solar noise. Numerous spikes are ignition
and other noise.
The sun's position can be used to "boresight" an amateur
antenna. The dish is peaked carefully on the sun at a time and
date listed in the Nautical Almanac, and the azimuth and elevation
indicators are adjusted to read the azimuth and elevation given
in the tables for that moment. This requires knowing the latitude
and longitude of the antenna site precisely, and making the
test at the correct time.
A Quiet Summer Ends Dramatically
Noise varied monotonously between 3 and 4 db. through the
summer of1966. QST reported an aurora on July 7-8, and Sky and
Telescope mentioned a big flare on July 11, but solar noise
recordings on or about these dates gave no hint of anything
out of the ordinary. Obviously measurements made during a brief
period daily do not tell the whole story, and short-term events
can be missed entirely. By late August the daily routine of
shooting the sun had become just that: a routine. Interest was
Then on August 29 a reading of 4.7 db. was obtained. Sunspot
records indicate that it was probably higher the previous day,
when a Class 3 flare and associated sudden ionospheric disturbance
(SID) occurred, but the 28th had been missed by this observer.
Here was the big change sought all summer. Would there be an
aurora? Indeed there was! QST reported auroral v.h.f. communication
on Aug. 29, 30 and Sept. 1 through 4. The evening display of
Sept. 3 was the best aurora in years, according to Sky and Telescope,12
and amateur results on 6 and 2 bear this out. An inconvenient
work schedule and too much reliance on "N7" transmissions by
WWV caused the writer to miss the big event!
This called for careful monitoring of the sun for the remainder
of the month, with results shown in Fig. 5. Solar noise is plotted
by the solid line, and American sunspot numbers13
by the broken line. Aurora dates are identified by the symbol,
A. Note the high level of solar noise and sunspot number on
Aug. 29, followed by a rapid drop to the low point Sept. 3,
the period of auroral activity. Solar noise peaks were observed
again on the 16th and 20th, and corresponding sunspot maxima
occurred on the 17th, 19th and 21st. Both started dropping,
and reached a low point on the 27th and 28th. No radio aurora
was reported around the noise peaks of the 16th and 20th, but
visual sightings were reported by Sky and Telescope. QST reported
50-Mc. DX Sept. 21.
Fig. 5 - Correlation between sunspot number
and 432-Mc. solar noise is shown clearly by this graph. Dates
when aurora was observed are indicated by the circled A.
The graph indicates that 432-Mc. solar noise and sunspot
numbers are related, and vary in the same general way. One can
see readily that there is also a correlation with aurora. It
would also appear that during September the sunspot maxima and
minima tended to trail solar noise highs and lows by a day or
so. This is not always the case. Records for eight other months
show noise peaks and sunspot maxima coinciding, and occasionally
the sunspot count has peaked a day in advance of the noise.
Fall and Winter
During October solar noise was measured every day but three.
Auroral propagation on 50 and 144 Mc. was reported by W1HDQ
Oct. 3, but noise and sunspot figures for the period didn't
indicate it. Presumably this was a 27-day recurrence of the
disturbance of early September. There was a noise peak on the
20th that coincided with maximum sunspot number (82) for the
month. The Ottawa Algonquin Radio Observatory report for October
shows solar flux at 2800 Mc. also peaked this day, but there
were no radio aurora reports. Sky and Telescope confirms that
there was a small aurora on the 20th. Transequatorial propagation
on 50 Mc. was observed by PY5GK on 14 days in October, including
the 21st, but not the 20th.
Shortened daylight hours reduced our opportunities for daily
observations in November and December. Solar noise high for
November was only 4.1 db., but activity picked up in December.
High noise reading for the last month of the year was 4.75 db.
at 1900 GMT, Dec. 13. There were no reports of aurora. (Statistically,
aurora is rare in this hemisphere in December - Editor). Sagamore
Hill Observatory reported an outstanding solar radio emission
on 2695 Mc. at this time, and American sunspot numbers were
at their month high on the 13th. A week later noise readings
reached a low point, and then began an upward climb toward the
end of the month. A good indicator of general solar activity,
for the writer, has been the number of days per month that solar
noise reached 4 db. or higher. December had 13 such days, compared
with only 5 in November, for almost the same number of observing
No observations were made the first few days of 1967, but
when they were resumed Jan. 5 a whopping 5.1 db. was recorded,
and it was up to 5.6 db. the following day. The alert was sounded,
and participants in the V.h.f. Sweepstakes the weekend of Jan.
7-8 don't need to be told what happened. Working schedules the
next few days prevented observations, but on Jan. 10 a high
of 4.75 db. was recorded. Three days later, Jan. 13-14, another
auroral session was reported. Like that of Jan. 7-8, it was
violent and widespread, yet January is normally a relatively
quiet month for aurora. Solar activity continued high, and every
day when observations could be made found noise exceeding 4
The first day of February a high noise reading of 4.6 db.
was obtained, and on the 4th an all-time high of 6 db. was logged!
Three days later, on the 7th, another aurora was enjoyed by
the v.h.f. gang. Activity continued high, with readings of 4.7
db. on the 7th and 4.5 db. on the 8th. Readings then settled
down to about 4 db. There was no indication of aurora on Feb.
16, about the time that a recurring disturbance might have been
expected. It would appear that some of the "repeaters" (auroras
recurring on the 27-day solar rotation cycle) are not associated
with solar noise readings, or the related noise peaks are of
short duration and are easily missed.
Readings continued at 4 db. until Feb. 23, when a moderate
rise to 4.5 db. was observed. Something new to the writer was
recorded on this date: a noise burst some 3 db. above the average
level, lasting about 90 seconds. See Fig. 6. On the 25th solar
noise was peaking at 4.6 db. A minor aurora was reported on
Fig. 6 - 90-second burst of solar noise
recorded at 1613 GMT Feb. 23, 1967. Peaks Were some 3.5 db.
above the normal solar noise level.
The Overall Picture
Highlights for the period June 1, 1966, to March 1,1967,
are shown in Table I. The monthly mean value for American sunspot
numbers is included to show the relationship of sunspot count
to solar noise. No doubt results might have been different if
noise readings had been made every day, or for longer periods
of time. Nevertheless, the figures do show that solar radio
noise and solar activity have been increasing since June, 1966,
and are still climbing. During the entire period there were
no changes made in equipment or measuring procedure. Any known
causes of error have been noted. Various r.f. amplifiers were
tested and compared from time to time, but only the units described
were used for the recorded data. Periodic checks of tubes and
regular measurement of noise figure was done in an effort to
obtain consistent results. The unchanging performance of the
transistor r.f. stages contributed much to the system reliability.
Paul Wilson, W4HHK, at work on the 18-foot
dish used to make solar noise measurements on 432 Mc. The driven
element and its circular plane reflector are just above the
Our 432-Mc. solar patrol has provided some answers to questions
raised at the beginning, but more information is needed. The
receiving system has performed about as expected, except that
the azimuth beamwidth of the antenna is almost double what it
should be, probably because an 18-foot dish is "small" in terms
of wavelength at 432 Mc., and thus the dipole does not simulate
a point source, as it must for optimum performance with a parabolic
reflector. Vertical beamwidth is correct, about 9 degrees.
A minimum of about 3 db. of solar noise was always obtained,
even during periods of little or no solar activity. When used
with care, solar noise readings under quiet conditions can be
used to evaluate systems, and make comparisons between antennas,
r.f. amplifiers and so on. By comparing readings with other
amateurs, a v.h.f. operator can determine if his system is "in
the ball park," which can be very helpful in setting up for
moonbounce work, for example. But beware! Solar noise measurements
are subject to error and variations, just as noise figure measurements
Regular observations do give an indication of solar activity,
but the solar noise level is not an exact indicator of sunspot
number. For example, the AA VSO daily sunspot count has varied
from 1 to 89 for noise readings of 3.5 to 3.6 db. Sunspot number
is usually in the range of 1 to 50 for a 3.5-db. noise level.
Auroras are associated with high solar noise levels, the .(
magic number" for the writer apparently being a minimum level
or about 4.7 db. This level and higher has been observed on
ten separate occasions, and seven individual auroras, apparently
related, have been reported. Aurora appears more likely when
high noise levels are observed on two or more successive days.
Delay between noise peak and aurora has been one to three days,
though some occurred on the same date. More observations should
give a clearer picture, and improve forecasting. Thus far the
relationship of F2 and transequatorial 50-Mc. propagation
to solar noise is not well defined, though this could improve
when the F2 layer rises into the 50-Mc. region more
consistently.14 Sporadic-E seems hardly related,
if at all.
The equipment and techniques described should not be considered
the ultimate or best way. This is simply an account of a 432-Mc.
experiment, in the hope that it will shed some light on the
subject as it relates to amateur v.h.f. enthusiasts, and perhaps
stimulate others to do similar work. Possibly observations by
a number of stations could be coordinated to provide an auroral
warning service for the v.h.f. community, during the peak years
of Cycle 20.
The writer owes special thanks to Third Army MARS for the
dish and related equipment; to WIHDQ for propagation reports;
to Sky and Telescope for auroral reports; to the American Association
of Variable Star Observers for sunspot data; to K2TKN, W3GKP,
W3O11, WA0IQN and others for their assistance in making this
Late Report On the afternoon of May 23, W4HHK recorded solar
noise on 432 Mc. in excess of 15 db. Visual observation showed
exceptionally large spots approaching the center of the solar
disk. On May 25 came the most widespread auroral display in
recent years. V.h.f. communication via the aurora was reported
as far south as Sarasota, Florida, and auroral contacts were
made in Southern California for the first time. The disturbance
continued through May 30, with peaks on the 25th, 28th and 30th.
For more details. see The World Above 50-Mc., July QST.
Table 1 - 432 Mc. Solar Noise June, 1966-February,
1967 (*) From Sky & Telescope Magazine.
1. Bray and Kirchner,
"Antenna Patterns from the Sun," July, 1960, QST, p. 13.
NBS Monograph 80, "Ionospheric Radio Propagation," April 1,
1965, p. 38. Price $2.75, from Supt. of Documents,
Washington, D. C. 20402.
3. M. H. Cohen, Cornell
University "Measurement of Solar Radiation at 430 Mc ." Quarterly
Status Report, Feb. 1-July 31, 1965.
World Above 50 Mc.," October, 1965, QST, p. 112
Reference 2, p. 43.
6. Moore, "Aurora and Magnetic
Storms," June, 1951, QST, p. 16.
7. "The World
Above 50 Mc., October, 1960, QST, p. 112.
"IT & T Reference Data for Radio Engineers, 4th Edition,
9. Tomcik, "The Aurorascope;" July, 1964,
QST, p 43.
10. "Nautical Almanac for 1967," Supt.
of Documents, Washington, D. C. 20402. Price $3.50.
"U. S. Navy Hydrographic Office Tables of Computed Altitude
and Azimuth," Latitudes 30 to 39 degrees, inclusive.
Pub. No. 214, Vol. IV. Order volume applicable to your latitude,
from Supt. of Documents, Price $3.00.
Activity Increases," Observer's Page, Sky and Telescope, December,
1966, p. 380.
13. American sunspot numbers derived
by the American Association of Variable Star Observers (AAVSO),
in Sky and Telescope.
14 The correlation between solar
activity and extreme peaks of F2-layer m.u.f. was
first observed by G6DH in the 1930's. For
his slant on it, relating to 50-Mc. DX, see "Any DX Today?"
January, 1948. QST, p. 27. The correlation with transequatorial
.50-Mc. DX is indicated in a summary of 1950 work by South American
50-Mc. operators, in "The World Above 50 Mc.,"
May, 1950, QST, p. 49.
Posted September 24, 2013