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December 1960 Radio-Electronics
 [Table of Contents]
Wax nostalgic about and learn from the history of early electronics.
See articles from Radio-Electronics,
published 1930-1988. All copyrights hereby acknowledged.
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Radio-Electronics
magazine founder, editor, and publisher Hugo Gernsback wrote this "How Far Amplification?"
article in 1960. In it, he briefly discusses the history of radio signal detection
and amplification in the preceding 60 years, and then projects what the state of
the art might be 60 years henceforth. Relative to 1960, that would be the year 2020,
which is already four years old. In 1960, the electronics world was transitioning
from vacuum tubes to solid state devices, so vast improvements in low noise and
amplification factors were being made. Mr. Gernsback, the remarkable futurist
that he was, foresaw generally the extremely low noise figure amplifiers of today,
which enable higher levels of amplification before the signal-to-noise ratio renders
further amplification useless. Interestingly, he did not mention the theoretical
noise floor of -174 dBm/Hz, which except maybe for spread signal communications
imposes a fairly hard limit on how much amplification is useful. At that level,
an amplification factor of 10(174/10) = 1017.4 = 251 quadrillion,
only gets the signal to 1 mW (in a 1 Hz bandwidth). That's a lot of amplification!
Of course most signals of interest occupy a bandwidth of much greater of 1 Hz.
Even so, a 10 kHz bandwidth signal still represents a multiplication factor
of 1013.4, or 25.1 trillion, to get to 1 mW.
How Far Amplification?
By Hugo Gernsback
... It Is Doubtful That Ultimate Amplification Is Possible Soon ...
When Marconi in 1901 sent his historic letter S across the ocean, a distance
over 2,000 miles, from Poldhu (England) to St. John's (Newfoundland), he used what
was then considered a terrific amount of power (20 kilowatts) to do so. The reason:
modern electric amplification was unknown. Hence his primitive auto-coherer (detector),
even with a high antenna, was just sufficient to intercept the faint signals over
the single 'phone he used at that time.
True electronic amplification was not possible till the advent of de Forest's
vacuum tube and the principles of regeneration, superregeneration and amplification
using a number of tubes in cascade, each step amplifying the original signal enormously.
Today's radio amateur can easily communicate with his friend at the antipodes
with a transmitter that uses but a few dry cells and has a power output of only
a few watts. To achieve this, the signal is amplified hundreds of millions of times
at the receiver; yet only a minimum number of vacuum tubes or transistors are used.
Spectacular as these results are, amplification at present has its limitations.
Vacuum tubes cannot be added indefinitely in cascade because the tube noises are
amplified too, and very soon a point is reached where the inherent noises of the
receiver overpower the signal.
A similar condition exists in transistor receivers to a lesser degree. Nevertheless,
with each additional transistor the noise ratio increases, soon preventing further
magnification of the original signal.
As time goes on, the obvious remedy seems to lie in the greater and ever greater
sensitivity of the detectors used, as well as radically new amplifiers. It all started
with Hertz' detector, a wire with a brass ball on each end and formed into a loop.
You saw the result in the form of a tiny spark. Then came the Branley metal-filings
coherer, followed by the Marconi hysteresis-iron-wire-band detector, later the crystal
detector, then the vacuum tube, a while later the transistor. More recently new
low-noise amplifiers, the parametric amplifier and the maser, have appeared. These
produce very much less noise than do tube amplifiers, and hence can be used to amplify
signals that would formerly have been lost in receiver noise. This covers the comparatively
short time of some 60 years.
There would seem to be little doubt that as time goes on more and more sensitive
detectors will be invented. Amplifiers too will be vastly improved. It appears certain
that the amplifiers of 60 years hence will give many thousands of times greater
amplification than those we have today. This despite the fact that scientists will
tell you that you cannot drive amplification beyond a certain mathematical limit.
Their ideas stem from the fact that even if you succeed in eliminating all the extraneous
and inherent noises, you will then amplify the colliding electrons themselves. Very
true. Nevertheless, remedies for such an eventuality will be found, probably in
new applications of cryo-electronics, i.e., in hypercooled circuits, near absolute
zero, coupled with atomic power that generates the necessary supply current. Incidentally,
masers in use today already use cryo-electronics to reduce thermal noise to the
minimum.
Why the race for superamplification? In military missile detection, in submarine
detection, our present instrumentation is still, to put it bluntly, extremely crude.
We have made only a start in this direction.
Further, we still struggle with atmospheric and ionospheric interference of radio
waves; the quality of the signal is all too often not very good. This is particularly
true in radio astronomy, where all signals must pierce our atmosphere. As we have
mentioned before on this page, one remedy would consist of a lunar detecting center.
Then the highly amplified, powerful signal could be sent to earth without difficulty.
Despite atmospheric and ionospheric difficulties, we have been able to receive
radio signals over immense distances. In 1950, Professor Lovell and his associates
at England's Jodrell Bank radio observatory succeeded in registering radio signals
from the Great Nebula in Andromeda (M31) 2,000,000 light-years distant! The frequency,
incidentally, was 1.9 meters (158 mc). A light-year is the distance covered by light
traveling at 186,285 miles per second during one year, or almost 6,000,000,000,000
(6 trillion) miles. Radio astronomers really should call the unit a radio-year,
since they use radio waves, not light waves.
If Marconi's original letter-S signal had not been absorbed completely by the
ionosphere, it would be speeding out into space now almost 60 light-years-or 60
radio-years. Later, also more powerful, short-wave signals are 35 radio-years out
in space, winging through space to be intercepted by other civilizations, should
they exist in a neighboring world. But as our galaxy measures more than 100,000
radio-years across, it may be many thousands of years before our radio emissions
reach a radio-civilized planet of some galactic sun. Hence we cannot hope for an
early answer or other communications from some other intelligent world which has
known electronics for eons.
Furthermore, there is always the possibility that weak, attenuated signals from
other worlds have reached the earth for ages. But we have not intercepted them because
of our crude detectors and insufficient amplification.
It is one thing to intercept signals from a star naturally powered with billions
of horsepower. It is quite another proposition to detect signals with a moderate
power of 1,000 or 10,000 kilowatts that would originate from a planet inhabited
by intelligent beings. Such signals would arrive on earth 50 attenuated that we
would certainly not be able to intercept them for a long time, due to the present
crude state of our electronic art.
- H.G.
Posted June 20, 2024
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