Re: audio modulated SSTC

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Antonio Carlos M. de Queiroz" <acmq-at-compuland-dot-com.br> 

Tesla list wrote:
 >
 > Original poster: herwig.roscher-at-gmx.de

 > Does "linearity" in this context mean, that an increase of e.g. 20 %
 > of audio power should result in the same increase of RF power?

In this case what is wanted is that the generated RF envelope shall
follow the shape of the modulating waveform.

 > So, the reason for the non-linearity of class C amplifiers mainly is
 > the high-Q tank, which starts ringing (as class C operation is
 > switching this resonant circuit)?

It must ring to keep the output almost sinusoidal. It rings at
the carrier frequency.
The linearity problems have two reasons:
- The high Q tank takes many cycles to change the amplitude of
its oscillations significantly. The amplitude may be proportional
to the average voltage of the power supply, but the envelope of the
oscillation may not follow the modulation with enough speed.
- If the input signal is modulated and the class C amplifier
is used as a linear amplifier, there is the same problem, and
also another: the resulting amplitude after stabilization
is not proportional to the amplitude of the excitation, because
what the amplifier sees as input is only the clipped tops of
the input waveform.

Antonio Carlos M. de Queiroz