The Electrotape DM-20 is a transistorized microwave EDM. The first commercial unit, serial number 151, was unveiled in 1961. It yielded centimeter accuracy over distances from 100 meters to 40 kilometers, and in all weather conditions, day and night. Each unit cost about $6,000 and weighs about 25 pounds. For use, two units are needed, one to send the signal and the other to receive it. The DM-20 at the Smithsonian, serial number 402, was probably made in the early 1960s. It remained in production for about 20 years.
Cubic's involvement with EDMs began in June 1958 when the United States Army Engineer Research and Development Laboratory (ERDL) asked them to develop a domestic equivalent of the Tellurometer MRA/1. The first Micro-Dist, as the instrument was then known, was delivered early the next year. Like the Tellurometer, Micro-Dist used data compression by means of modulation side-band folding. With Micro-Dist, however, the two units were interchangeable. Other differences pertained to Cubic's diplexing system, receiver, and manner of digital readout. Micro-Dist operated at 10 Gigahertz. Cubic claimed an accuracy of 1:150,000 ± 2 inches. Micro-Dist was advertised as early as March 1959. In 1960, owing to a conflict with Tellurometer's Micro-Distancer, Micro-Dist was renamed Electrotape.
Another ERDL contract for a "miniaturized" instrument (this one for $55,000 and signed in 1959) led to the solid state DM-20, which was to be a domestic equivalent of the
Tellurometer MRA/2. The DM-20 was protected, in part, by patent #3,078,460 for "Electronic Surveying System" granted on February 19, 1963, to Robert V. Werner and Eddy Hose, and assigned to Cubic Corp. When aspects of the DM-20 appeared to infringe patents owned by the Union of South Africa and licensed to Tellurometer, Cubic and South Africa decided to cross-license their designs.
Ref: Cubic, Instruction Manual for Model DM-20 Electrotape.
Cubic, Cubic Model DM-20 Electrotape.