Bell Telephone Laboratories - Junction Diode Amplifier
November 1958 Radio News

November 1958 Radio & TV News

[Table of Contents] Wax nostalgic about and learn from the history of early electronics. See articles from Radio & Television News, published 1919-1959. All copyrights hereby acknowledged.

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)