Signal channels can have different-wavelength signals {multiplexing, electronics}.
Two radio signals at different frequencies can mix to make a beat frequency {heterodyne}|, for amplitude modulation.
Edwin Armstrong [1918] invented a Supersonic Heterodyne Receiver to convert a selected radio frequency, for amplification and filtering {superheterodyne}| {superhet}.
Optical channels can have different-wavelength signals {wave division multiplexing}| (WDM).
7-Machine-Kinds-Electronic-Effects
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Date Modified: 2022.0225