[Amps] IMD

[Gary Schafer]

There is no easy way to do audio clipping for SSB. The best way is to do RF
clipping followed by a band pass filter.
The problem is that the audio waveform is not the same as the RF envelope
waveform. It may look similar but operates entirely different.

Put a square wave audio signal into an SSB transmitter any you only get very
large spikes out.

73
Gary  K4FMX

> 
> A clipper made from couple of diodes back to back across the audio line,
> followed by a lowpass filter will get you most of the way there,
> particularly if preceded by a compressor (THAT Corp do a very nice chip
> that can be trivially configured as a compressor/limiter/gate).
> 
> The filter will of course introduce some overshoot and ringing, so a few
> stages may be indicated, but that is still only what a dozen or so
> components.
> 
> Or a pair of SL670s or similar and a 445Khz ceramic filter plus a few
> diodes makes a dandy RF speech clipper/filter combo.
> 
> I might draw one up and publish it somewhere.
> 
> Personally I consider any ALC voltage to be an indication that something
> is not set up right, you know the amps power rating and power gain, so
> you know the required peak drive power, program that into the exciter
> and leave the ALC line unhooked (My exciter does NOT overshoot, some do,
> be careful).
> 
> A reverse power sensor after the amp is a good idea if you go this way
> as the amp now has no way to fold back the exciter drive power.
> 
> 73, Dan.
> 
> 
> 
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