[TenTec] RF speech processors

Ken Brown ken.d.brown at hawaiiantel.net
Tue Feb 3 01:08:53 EST 2009

Hi all,

     I think I know what an RF speech processor is. First I'll describe 
what I think it is:

You connect your microphone audio to a little AM or DSB generator, 
working at some frequency such as 455 kHz. Then you compress or even 
clip that signal to increase the average power output. Probably goes 
though some bandwidth limiting filters. After that it gets demodulated 
back to audio, and feeds the microphone input of the SSB rig. Since the 
compression/clipping/whatever is done at some "intermediate frequency" 
and then demodulated back down to audio, the IMD "splatter" and 
harmonics that are generated, don't get transmitted. Only bandwidth 
limited audio goes to the microphone input of the SSB transmitter, and 
the SSB transmitter audio stages and RF stages are never driven into 
non-linearity. The transmitted signal bandwidth is limited by the usual 
crystal or mechanical filters. You get a really dense high average power 

     I'm sure I may be wrong in some of the details, yet I'm pretty sure 
I've got the basic principle right.

     What I don't get is, with DSP used in the transmit section of a 
modern rig, can't you write an algorithm running in the DSP system to do 
that, and do it better, without resorting to this old technology? I'm 
not saying it's bad. When a tried and true method works, it works. Just 
seems like this is one of those functions that DSP ought to be able to do.


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