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Heterodyne Signal Detection Invention

July 7th Fact-of-the-Day

Communication receivers use a Beat Frequency Oscillator (BFO) to make unmodulated continuous wave (CW) signals audible. If a BFO is tuned to a slightly different frequency than a CW radio frequency signal and the CW signal and the signal from the oscillator are mixed correctly, sum and difference frequencies are produced. The sum frequency is above the range of human hearing, but the difference frequency can be adjusted so it can be heard when it is amplified and applied to earphones or a loud speaker. (This process occurs at an intermediate-frequency, rather than at a received signal frequency, in modern receivers.) This method of CW signal detection was invented, named 'Heterodyne Detection,' and patented by Canadian-born Reginald Aubrey Fessenden (working in the U.S.) in 1902 before methods of generating continuous wave RF signals or of making Beat Frequency Oscillators had been invented. ©2005 Martek International All rights reserved.

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