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Message-ID: <5.1.0.14.0.20020129144512.02f80bf0@gemini.herts.ac.uk>
Date: Tue, 29 Jan 2002 15:12:08 +0000
To: rsgb_lf_group@blacksheep.org
From: "James Moritz" <j.r.moritz@herts.ac.uk>
Subject: Re: LF: PSK31 generation
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At 14:12 29/01/2002 +0100, Johan wrote:
>...Perhaps I am missing something, but as far as I can see,
>the waveform *will* be symmetrical if the drive to each totem pole has a 
>50/50 duty
>cycle and the modulation is done only by varying the phase between the 
>totem pole
>drivers 0 - 180 degrees.

Dear Johan, LF Group,

Yes, It will - I hadn't thought of it quite like that before...If you have 
4 output devices in a bridge configuration, there are many different ways 
of driving them! Of course, any waveform that is symmetrical will have no 
even order harmonics.

It would take a little care to implement though; if the drive to only one 
of the totem poles was varied in phase, changing the output amplitude would 
also change the output phase, introducing up to 90 degrees unwanted 
additional phase modulation into the signal. This could be avoided by 
shifting the phase of both drive signals by equal and opposite amounts.

Cheers, Jim Moritz
73 de M0BMU