From: WarmSpgs@aol.com
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Date: Tue, 27 Mar 2001 11:32:24 EST
Subject: Re: LF: RE: WOLF (BPSK) modulation continuous phase modulation.
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In a message dated 3/26/01 12:06:05 PM Eastern Standard Time, 
j.r.moritz@herts.ac.uk writes:

<< But  unfortunately, any clipping or AGC will distort the amplitude 
 envelope, which in turn will re-introduce unwanted sidebands.  >>

This may be a matter of semantics, but clipping won't actually "re-introduce" 
sidebands.  While AGC would indeed distort the amplitude envelope and worsen 
sidebands, hard RF clipping eliminates envelope variations entirely.  The 
consequence of clipping is that we no longer have the envelope to help us 
further suppress the phase-modulation sidebands.  The sidebands themselves 
remain just as they would for any continuous-shift PSK signal--less energetic 
than for brute-force instantaneous PSK, but broader than if we retained the 
amplitude variations that accompany appropriate filtering.

The ideal case would be to generate a waveform based on root-raised-cosine 
filtering in the exciter, use envelope-elimination-and-recovery to amplify 
the signal at maximum efficiency, and use a corresponding filter at the 
receive end.

However, I believe the object of Rik's proposal was to decrease bandwidth 
while retaining as much simplicity in the system as possible.  If one can 
abide the slower phase transitions of the filtered signal, and the modest 
increase in bandwidth from not having dragged out the transitions even 
further, the technique should work at moderate power levels.  It's a 
collection of trade-offs, as is anything in engineering.

73,
John