The Infradyne Circuit
The Infradyne Circuit
The following is a summary of snippets previously found on the manufacturer's page, which I post here for better readability (and potential discussion).
Mark
In 1926 E.M. Sargent designed the "Infradyne Circuit" as a way to circumvent the RCA-Westinghouse held Superheterodyne patent and avoid an inevitable lawsuit. During the 1920s, no other company but RCA could legally sell superhets - or then "cross-licensed" companies, i.e. GE or Westinghouse. Kits could sometimes avoid legal problems. The Infradyne was originally sold only as a kit and by carefully avoiding the term "Superheterodyne", Sargent kept everything legal.
A few companies took their chances with legalities and sold completed Infradyne kits, such as the Remloc Radio Co.
The Infradyne circuit uses the sum of the incoming signal and the second harmonic of the local oscillator resulting in an IF frequency of 3500 kc. Since the sum is used, the local oscillator frequency must be reduced as the incoming signal frequency is increased so the IF will remain at 3500 kc.
Bruce McCalley wrote: "The Infradyne Receiver Introduced in the August 1926 issue of Radio, and was featured for several issues after that. The Infradyne was one of the more unusual designs of the early days of radio. In the early days of radio there were a good number of odd-ball designs introduced. Some of these were to enable better performance, some were to save on the number of tubes required, and some seem to defy reason. The Infradyne, to this writer, seems to fit the last of these categories." ... "The IF amplifier, called the "Infradyne Amplifier" used three '99 tubes on a separate chassis. It was manufactured by Remler, a division of Gray and Danielson Mfg. Co, San Francisco, California." By the way: Remler Company, Limited, was founded in 1918 and was in business until 1988.
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The infradyne circuit was not really integrated in commercial production and within months it was no topic anymore. Before some adds in the journal "Radio magazine" from different makers stated that their set is suitable for the Infradyne. The term has a "new life" in very modern technique since about 1990 - Publication: "Katsushi Iwashita, et al., Chromatic Dispersion Compensation in Coherent Optical Communications, Journal of Lightwave Technology, vol. 8, No, 3, Mar. 1990, pp. 367-375. Chris Cho-Pin Li, et al., Comparison of Coded and Uncoded QPSK Intradyne and Heterodyne Receivers, IEEE, 1993 pp. 1891-1895."
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