March 1948 Radio-Craft
Wax nostalgic about and learn from the history of early electronics.
See articles from Radio-Craft,
published 1929 - 1953. All copyrights are hereby acknowledged.
National defense needs have pushed back
the frontiers of science and technology since time immemorial. Mechanics, chemistry,
medicine, mathematics, psychology, astronomy, electricity, and as of the late nineteenth
century, electronics. Astronomy was useful as a navigational tool and required a very
sophisticated knowledge of geometry and algebra to make it accessible to seafaring men,
cartographers, and land surveyors. Since the early 1900s, radio astronomy has played
a huge role in the advancement of super-sensitive receiver designs. Most people think
of information arriving to them in two or maybe three forms: sound, visible light, and
some (but not many) even consider radio waves. As over-the-air
AM and FM radio broadcasts die out, even fewer people are aware of radio waves; they
certainly don't think of their WiFi or cellphone signals as radio or anything else for
that matter ((i.e., oblivious to what makes them work).
Certainly, only a very small percentage ever consider that night sky objects - which
of course are there during the daylight hours, too - emit electromagnetic radiation at
frequencies other than those of visible light. In fact, it has been discovered over the
last century that much more information exists outside the visible light band than within
it. Pulsars, black holes, and much of the history of the universe would not be known
if not for the study of energy other than that which we can see visually. When this article
appeared in 1948, Dr.s Arno
Robert Wilson had not yet, using the Bell Telephone Labs sugar scoop antenna in New
Jersey, identified the
cosmic background radiation left over from the universe's creation.
Articles here on RF Cafe which mention the Dr. Robert W. Wilson and Dr. Arno
The Maser & Sugar Scoop Antenna: Receiver for Signals from Space,
Bell Telephone Laboratories Project Echo,
The Amazing Maser: The Jewel That Conquers Space,
Signals from Sun and Stars, and
Cosmic Radio Signals
From Sun and Stars
Front view of the 25-foot Wurzburg antenna beamed at the sun.
The giant equipment illustrated on our cover and on this page is nothing more nor
less than a radio receiver. Further, it is a radio which receives static only! Building
a receiver to pick up static may seem pursuit of the nonessential, but the designer of
this set went even further. He built it to reject practically all the crackles and pops
we get on our broadcast radios and to receive static on very high frequencies only -
on the wave lengths at which the sun and stars radiate.
Scientists of the Bureau of Standards believe that knowledge of this cosmic static
- particularly of the radio waves generated by the sun - may be very useful to communications
engineers, astronomers, and meteorologists. It may help to expand greatly our knowledge
of the universe, and answer the old question: what effect have the stars and sun on this
world and on human life?
Ordinary static is too well known to the broadcast listener, particularly those living
within range of that great "radio center" of terrestrial static - the Caribbean thunderstorm
region. Individual flashes of lightning there combine to produce steady crashing, which
is transmitted over great distances.
Intensity of atmospheric noise drops off as the frequency increases, and finally ceases
to be a practical problem.
At that point cosmic radio noise takes over. Heard as a low, steady hiss, it may become
an important problem to the listener on high frequencies as radio equipment is improved.
Already advances in design of both v.h.f, and u.h.f. equipment have greatly reduced internal
noise from tubes and other components. High-frequency radio noise may then become the
factor which will limit the sensitivity of FM, television, microwave telephone, and similar
FM radio signals suppress this type of static within a certain range of the transmitting
station. At considerable distances from lower-power stations the strength ratio between
the FM program and the cosmic noise might be such as to drown out the program completely.
So the ordinary listener may find noise from the sun and stars an immediate and practical
subject of interest.
The project, which use the great Würzburg parabolic antenna shown here, will
observe and analyze radio noise generated by the sun, determining the range of frequencies
in the solar broadcasting spectrum and the strength at which they can be received on
this planet. It will also attempt to correlate solar noise with other solar, interstellar,
and terrestrial phenomena.
Two of these parabolic mirrors are now installed at the propagation laboratory of
the Bureau of Standards at Sterling, Virginia. Twenty-five feet across, they can capture
a large cross section of the solar energy beamed at the earth. The mirrors are controlled
automatically, like an astronomer's telescope, to follow the sun constantly through the
day. By using 2 receivers, different types of studies can be undertaken simultaneously,
or a broader band of frequencies can be followed. The first receiver - now being installed
- will be used initially for studies ranging 480 to 500 mc.
Solar noise appears to be fundamentally the same as cosmic noise, and is heard as
a steady hiss whenever the operator substitutes a pair of headphones for his recorder.
It has also an undulating component superimposed on the stable noise, with variations
sometimes of great rapidity, which sound like puffs or swishes lasting a second or less.
The swishes sometimes overlap, resulting in a grinding noise. This may manifest itself
on the screen of a standard television set as streaking or picture jumpiness. Occasionally
there are intense, prolonged bursts of solar transmission lasting several hours (see
Sunspots and Radio, by Harlan True Stetson, in Radio-Craft, February, 1948). These cause
a radar to "go blind" when pointed in the sun's direction.
Like many other important scientific projects, the cosmic-noise study started as an
amateur effort. The existence of cosmic radio waves had long been suspected - they had
even been given a name, the Jansky effect. Among the students of this effect was an Illinois
radio engineer, Grote Reber, who built a large sheet-metal parabola and for some years
spent most of his nights collecting records from various parts of the sky. Among his
important discoveries was that the center of the Milky Way is a powerful source of cosmic
radio energy. His work attracted the attention of the Bureau of Standards, already interested
in the problem of the sun's effect on radio propagation. Unquestionably the leading student
of cosmic radio in the United States, he was called in to head the solar radio study
project, exchanging his sheet metal parabola for the big Würzburgs. The, home-built
mirror, however, is still doing duty in studies of radiation from the stars. The Bureau,
at present chiefly interested in the sun's broadcasts, has 2 important problems to solve
in the field - of cosmic noise: first, the question of intensities-vs-frequencies - in
other words, on what bands are the stars and star-clouds radiating, and what bands come
in strongest; second, mapping the sky's sources of cosmic signals. The Milky Way center
is already known to be a strong source. Another one is in Cygnus (the Swan). Cause of
the radiations is not definitely known. It has been suggested that, because of the similarity
of the sound produced in the radio receiver, it may be due to thermal agitation of charged
particles. The billions of stars which constitute our galaxy, say the Bureau's scientists,
throw off a large amount of material which expands and tends to fill from the intervening
space as a very thin gas. These atoms of gas may be ionized by starlight, producing positive
and negative particles which radiate both visible light and radio waves.
A notable feature of the radar method of exploring the heavens is that such areas
of activity may be located even though they may be hidden (as in the case of the Milky
Way center) by dense dark clouds which would baffle astronomers. The "electron telescope"
may extend the knowledge of the astronomer as much as the electron microscope has already
broadened the horizons of the searcher into the realm of the infinitesimally small.
Practical applications of the new study are expected to be immediate. For example,
a radio sextant might be built which would shoot the sun by noting the direction of arrival
of solar noise. Such an instrument would be a boon to navigation in foggy areas. Knowledge
of solar radiation conditions would also be valuable in short-range forecasts of radio
propagation. But by far the greatest value of the study is likely to be the gaining knowledge
of things not now understood and possibly not dreamed of theory.
For example, when Grote Reber pointed his radio telescope at the Milky Way center,
he rather expected to find a center of radio noise intensity. Most galaxies have a dense
central nucleus, but the center of ours - if it exists - is hidden in dark clouds presumably
of cosmic dust. The burst of signal strength from that area confirmed the suspicions
of astronomers, and proved that the radio telescope could make discoveries denied even
to Palomar's great light lens. But no one knows the cause of the intense source of signals
in the constellation of Cygnus. Investigation of this and other discoveries which are
almost certain to be made is likely to give us a new grasp of the universe, and will
more than likely help to give us better radio reception right on this earth.
Posted January 27, 2015