Bell Telephone Laboratories - Pipe Circuits
November 1948 Radio & Television News

November 1948 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.

I have always been a stickler for creating neat, orderly arrangements when building any type of circuit assembly. Many moons ago when starting out as an electrician, I made a point of installing straight runs of Romex type cable with no twists, evenly spaced staples, and keeping the identification marking to the outside. Conduit was precisely bent and installed, again with organized parallel runs and even spacing where possible (all while conforming to the NEC). Circuit breaker panel wiring looked like something seen in an Apollo space capsule (ok, I exaggerated a bit here). Electrical inspectors often complimented my work. Moving on to an electronics career, the habits carried over when prototyping and even when directing layout for production PCBs or chassis assemblies, including cabling. The greatest enjoyment I had was when laying out runs of waveguide. Standardized manufactured straight and corner bends, along with integral components like switches, couplers, circulators, etc., to some extent guaranteed a nice-looking configuration, but a thoughtful planning guaranteed an impressive result. Rectangular waveguide always looks more high-tech IMHO since circular waveguide can look like coaxial cable (if you overlook the bolted flanges). This advertisement by Bell Telephone Labs highlights waveguide circuits used in their relatively new (in 1948) microwave long distance relay distribution system. For a company that really had no domestic competition at the time, Bell Labs put a lot of effort into promoting their work.

Bell Telephone Laboratories Ad: Pipe Circuits

Unlike radio broadcast waves, microwaves are too short to be handled effectively in wire circuits. So, for carrying microwaves to and from antennas, Bell Laboratories scientists have developed circuits in "pipes," or waveguides.

Although the waves travel in the space within the waveguides, still they are influenced by those characteristics which are common to wire circuits, such as capacitance and inductance. A screw through the guide wall acts like a capacitor; a rod across the inside, like an inductance coil. Thus transformers, wave filters, resonant circuits - all have their counterpart in waveguide fittings. Such fittings, together with the connection sections of waveguide, constitute a wave-guide circuit.

From Bell Laboratories research came the waveguide circuits which carry radio waves between apparatus and antennas of the New York-Boston radio relay system. As in long distance wire communication, the aim is to transmit wide frequency bands with high efficiency - band widths which some day can be expanded to carry thousands of telephone conversations and many television pictures.

Practical aspects of waveguides were demonstrated by Bell Telephone Laboratories back in 1932. Steady exploration in new fields, years ahead of commercial use, continues to keep your telephone system the most advanced in the world.

3 - The waveguide connects with antennas, which are

     oriented in azimuth with antennas at next station.

Bell Telephone Laboratories

Exploring and Inventing, Devising and Perfecting for Continued Improvements and Economies in Telephone Service

Posted November 27, 2019
(updated from original post on 12/10/2015)