Zwischenharmonische
(interharmonic)
Sinusförmige Schwingungen, deren Frequenzenkein ganzzahliges Vielfaches (µ) der Netzfrequenz sind.

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Note added at 2 hrs 59 mins (2005-10-26 19:33:54 GMT)
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Interharmonic is any signal who's frequency is not an integral multiple of the fundamental signal's frequency. For example, if the fundamental's frequency is 1 MHz, then the first harmonic's frequency would be 2 MHz, the second, 3 MHz, etc. A signal with a frequency of, say, 1.5 MHz would be, ipso facto, an interharmonic.

So an interharmonic isn't really a harmonic at all. At least not of the fundamental signal in question.