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.
Cosmic Radio Signals
From Sun and Stars
Front view of the 25-foot Wurzburg antenna beamed at
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 equipment.
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
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