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The Inverted L Antenna by Don Adamson      Early radios, especially crystal sets, needed a long antenna for good operation. Here's an overview of the most common type of antenna used with home radios and crystal sets in the 1920s and early 1930s: the inverted L antenna.      An inverted L antenna was simply a length of wire suspended above the ground. A lead-in wire was connected to one end and brought into a house.      In the 1922 book "Radio for Everybody," Lescarboura recommended an antenna using No. 14 or 16 copper wire at least 30 feet above the ground with a length of about 75 feet for broadcast band reception: A - screw eye; B - rope; C - pulley; D - rope; E - insulator; F - antenna; G - insulator; H - rope; I - screw eye; J - lead-in wire; K - lightning switch; L - ground wire; M - ground pipe; N - lead to receiving set; O - insulating tube      Antennas were erected as far away as possible from other objects like chimneys, metals roofs, gutters, drain pipes, other antennas, trees, and especially power and telephone lines.      Long-wire antennas could be slightly directional: they sometimes received best in the direction away from the free end (to the right in the picture above).      The insulators were usually made of clear glass, and were used to electrically isolate the antenna from its supporting structure, usually buildings or masts. Connection to trees was not advised, since they could sway too much with strong winds.      The lead-in wire was sometimes run down the side of a building. This insulated wire was isolated from the side of the building with porcelain stand-offs. The stand-offs had nails through their centers, and the insulated wire was sandwiched between the two porcelain pieces and nailed to a wall. Glass antenna insulator, about 3½ inches (left); porcelain stand-off, 2 inches when closed (right); both of these items came from the Birnbach Aerial Kit shown in the galleries.      The lead-in wire was brought into the house inside a porcelain tube. A window lead-in strip could also used; this was a black, insulated wire strip with fahnestock clips at either end. It was placed across a window opening, and the window could be closed on top of it.      Ground connections were very important. Inside the house, the receiver was connected to ground via a copper strip clamped around a cold water pipe. Outside, the ground was a long metal stake or pipe driven into the ground. Lightning arrester placement in antenna circuit, from Anderson (left); CORWICO lightning arrester, about 4 inches (right)      The receiver was protected from lightning through use of a knife switch or a lightning arrester. An arrester was simply a small air gap; static charges would find it easier to cross the air gap to ground than go through the radio receiver to ground.      As technology developed and the sensitivity of radio sets increased, more and more receivers could get by on a simple short piece of wire or a built-in loop antenna. The proliferation of radio stations also helped eliminate the need for long receiving antennas. References      Radio for Everybody, Lescarboura, Austin C., Scientific American, 1922      Audels Radiomans Guide Covering Theory, Construction, and Servicing, Anderson, Edwin P., Theo. Audel & Co., 1944      The Boys' Second Book of Radio and Electronics, Morgan, Alfred, Scribner's, 1957 Disclaimer: This is not a "how-to" article. Working with antennas and electrical devices (especially old ones) can be dangerous, and mistakes can be fatal. If you decide to work with such things, it is solely your responsibility to work safely and to know what you're doing. -DJA

Copyright © by Don Adamson. All Rights Reserved.