Re: VS: [WSJTX] Q65 and non-linear RF power amplifiers #Q65


Peter Hall, VK6HP
 

Hello Steve,

I was the poster who raised the issue with the FST4(W) waveforms in this forum and in the RSGB LF group.  You can see the later part of the discussion here:

https://wsjtx.groups.io/g/main/topic/79269122#20188

The problem arises because, at some point in the chain, the analog drive signal has to be converted to digital form, preferably with as little jitter as possible.  Typical squaring circuits have a dead or indeterminate band - however tiny - and, with very slow envelopes, produce erratic pulse drive to the (very widely used) Class D or E PAs, the designs of which typically requires a well-tempered pulse train.  As you see from the previous discussion there are several solutions possible, the most satisfactory being the setting of the environment variable as outlined by Bill.

I haven't tried Q65 yet but can do so in the next week.  Whether there's a problem will depend on the how slow the envelope rise and fall is.  I agree it'd be handy to have some descriptions or, better yet, sketches of the various WSJT mode signals.

73, Peter.

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