HARMONIC(S) A periodic signal of frequency f can be described as the sum of sinusoidal signals of frequencies f, 2 x f, 3 x f etc. The sinusoidal signal of frequency f is called fundamental wave. The sinusoidal signals of frequencies 2 x f, 3 x f etc. are called harmonics.
HARMONIC DISTORTION A real active circuit will always generate harmonics of the input signal. The level of these harmonic products is a growing function of the input signal level. The 2nd and 3rd order harmonic distortion ratios of the input stage of a spectrum analyzer are determining factors for the dynamic range of the analyzer.
HARMONIC MIXER A mixer which utilizes the 2nd order harmonic distortion of the local oscillator frequency to convert the RF input signal to the IF level:
fIF = |fRF - n x fLO| where n = 2, 3, 4 etc. The harmonics are either present in the LO signal or are generated in the mixer from the fundamental of the LO signal.
