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Rudolf Engelbrecht, an alum of Oregon state University, was inducted into the
institution's Engineering Hall of Fame in 1998. As evidenced in this full-page advertisement
in a 1958 issue of Radio & TV
News magazine, Mr. Engelbrecht's work was instrumental in advancing
the state of the art in communications electronics while an engineer at
Bell Telephone Laboratories
(aka Bell Labs). Here, he is show with the four-stage junction diode amplifier developed
for military applications. It exploited the variable capacitance nature of a
varactor type diode
to effect amplification in the UHF and microwave bands. Engelbrecht went on to work
at Radio Corporation of America (RCA) later in his career. BTW, if you are wondering
what other kind of diode might there be other than a "junction" diode, the answer
is that the earliest semiconductor diodes were "point
contact" types which used a sharpened metal wire to make contact with the semiconductor
substrate. Of course before that were
vacuum tube
diodes, but they're not semiconductor-based.
Bell Telephone Laboratories Ad
 New amplifier battles "noise"
Four-stage junction diode amplifier was developed at Bell Telephone Laboratories
by Rudolf Engelbrecht for military applications. Operates on the "varactor" principle,
utilizing the variable capacitance of diodes. With 400-mc. signal, the gain is 10
db. over the 100-mc. band.
The tremendous possibilities of semiconductor science are again illustrated by
a recent development from Bell Telephone Laboratories. The development began with
research which Bell Laboratories scientists were conducting for the U. S. Army Signal
Corps. The objective was to reduce the "noise" in UHF and microwave receivers and
thus increase their ability to pick up weak signals.
 The scientists attacked the problem by conducting
a thorough study of the capabilities of semiconductor junction diodes. These studies
led to the conclusion that junction diodes could be made to amplify efficiently
at UHF and microwave frequencies. This was something that had never been done before.
The theory indicated that such an amplifier would be exceptionally free of noise.
At Bell Laboratories, development engineers proved the point by developing a
new kind of amplifier in which the active elements are junction diodes. As predicted,
it is extremely low in noise and efficiently amplifies over a wide band of frequencies.
The new amplifier is now being developed for U. S. Army Ordnance radar equipment.
But it has numerous other possibilities. In radio astronomy, for example, it could
be used to detect weaker signals from outer space. In telephony, it offers a way
to increase the distance between relay stations in line-of-sight or over-the-horizon
communications.
 Bell Telephone Laboratories
World Center of Communications Research and Development
Posted April 8, 2024
(updated from original post
on 12/31/2017)
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