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Harmonic distortion results from non-linear amplifier gain and appears as output
signals at integral multiples of the input signal frequency. Since harmonic
distortion is a function of input power, it is usually specified in terms of the
relative level of the harmonics with respect to the power of the fundamental
signal.
The actual broadband characteristics of the amplifier (which may be wider than
the required passband specified) may present significant gain at harmonic
frequencies and thereby increase the harmonic output.
Harmonic content is related to the device distortion and the frequency response
of the circuit modules used to build the amplifier. The input and output
networks are the major components in determining passband response.
Second harmonics occurring within the passband of the amplifier will typically
be -12 to -15 dBc at the amplifier's specified 1 dB gain compression point.
Third harmonics are typically an additional 5 to 7 dB below this level. As the
circuits passband narrows, the resulting second and third harmonics attenuate
rapidly.
(of a Mixer)
The ratio (in dB) of distortion to the IF output waveform caused by
mixer-generated harmonics of the RF and LO input signals. This characteristic
is extremely dependent on input frequency, RF and LO signal levels and the
precise impedance characteristics of all terminations at the operating
frequency.
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