Re: [Amps] OT: RF Speech Processor Kits - Final Final

[Gary Schafer <garyschafer@comcast.net>]

Steve Thompson wrote:
> Ken G3WCS wrote:
>
> > Thank you to everyone who contacted me both on and off list.
> >
> > Quite a lot of folk pointed me to audio clippers rather than RF
> > Processors. Just for the information of the guys who don't know, there
> > is a difference between the two.
> >
> > An audio clipper simply either compresses or clips (or both) the audio
> > signal. This can (and often does) result in 'whiskers' or splatter
> > which make the transmitted signal wider. This was not the design I
> > was looking for.
>
> Just for the record, can I mention that the split band audio clipper I
> referred to isn't a simple compressor/clipper that generates lots of
> harmonic distortion and splatter. By splitting the audio into sub-octave
> bands you can clip each one, and then remove the harmonics, before
> recombining so you end up with the same effect as rf clipping.
>
> Steve

The problem with audio clipping for an ssb transmitter is that the audio 
wave form is not the same as the ssb wave form like it is on AM.

A square wave fed to an AM transmitter produces a square wave out.
A square wave fed to an ssb transmitter produces an infinite spike in 
its output.

When you clip audio you produce square waves. The more clipping the more 
near to ideal square waves you produce.

At high audio frequencies you can filter out the squared components and 
round them off somewhat and get rid of some of the high frequency 
component in the square wave. At the lower audio frequencies more of the 
harmonics fall in the audio band that you can't filter out.

The split band processors help in that they can filter out more of the 
unwanted components. But you still have the square wave problem being 
fed to the ssb transmitter although not as bad as with conventional 
audio clipping.

The reason that most audio clipping systems cut the low frequencies 
before clipping is to eliminate a lot of the trash from clipping as the 
low frequencies give the biggest problem when you are clipping.

Rf clippers solve those problems because all of the harmonics from 
clipping fall outside the bandpass of the rf filter.

73
Gary  K4FMX





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