heterodynen
Heterodynen, or heterodyning, is a signal-processing technique in which two signals of different frequencies are mixed. A nonlinear device outputs components at the sum and the difference of the input frequencies, |f1 − f2| and f1 + f2, as well as higher-order products. The presence of multiple frequency components stems from the nonlinearity of the mixer, diode, transistor, or other nonlinear elements used to combine the signals. The difference frequency often serves as a beat note or baseband information, while the sum and other products may be filtered or suppressed.
In radio and communications engineering, heterodynen are used to translate signals to more convenient frequencies. The
Optical heterodyning extends the concept to optical frequencies, using a local-oscillator laser to beat two optical
Historically, heterodyning became central to radio technology with the development of frequency conversion methods in the