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Microphone Month 2


The combining of two radio frequency or light waves to produce two new frequencies that are the sum and differences of the two. Anytime two similar waves are combined, sum and difference sidebands will be produced (also see WFTD Beats for more background on this). Specifically, heterodyne usually refers to combining a received radio wave with another wave generated inside an apparatus. This phenomenon is utilized in Superheterodyne receivers, which were originally developed in 1918. Superhetrodyne receivers overcome several deficiencies with typical tuned receivers, most notably poor frequency stability, and poor selectivity as even the high Q filters available at the time had too much bandwidth in the upper radio frequencies. The heterodyne process is used to convert a high incoming frequency to a lower, more manageable frequency. This is accomplished by tuning a built-in oscillator to frequencies that cause beating between it and the incoming signal. This beating produces sum and difference sideband frequencies, the lower of which (the difference frequency) can be more readily handled by the available electronics in a lower cost receiver. A big advantage of this approach comes from the fact that the radio receiver’s electronics can be tuned to a very narrow and fixed frequency. The incoming signal is “tuned” to fall into this range by adjusting the oscillator and the corresponding heterodyne action. Radio transmitters also utilize this technology. In fact, you’ll find it in a large majority of radio transmission and receiving equipment available today.

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