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Re: R: Re: LF: TXing 2200m WSPR

To: [email protected]
Subject: Re: R: Re: LF: TXing 2200m WSPR
From: N1BUG <[email protected]>
Date: Fri, 29 Dec 2017 08:35:59 -0500
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Thanks Andy. Assuming by driver stages you mean what is external to the PA, the exciter. This is one reason I tried driving it with the function generator (HP 3325B) instead of the usual exciter (QRP Labs Ultimate 3S). There was no change at all in the undesired behavior. How likely can it be that two very different drivers would be affected to exactly the same degree?

Of course it can be feedback from output to input within the PA itself. That's what I was suspecting, and that somehow this feedback is triggered by a load that is highly reactive off frequency. But it's just a wild guess, I really don't know what is happening. Perhaps I can manage to screen the input circuit.

Paul N1BUG



On 12/29/2017 07:06 AM, Andy Talbot wrote:
Sounds more like feedback.    RF feeding back into the driver stages.   The LF component you see is, perhaps, a beat between generated RF and oscillatory RF due to feedback. Or feedback itself oscillating at LF.  Or something like that

Vaguely recall something similar happening here in the dim and distant past.   Perhaps a couple of times even    In fact, I think it explains why my 475kHz 400W Class-E PA which is built open-style has an aluminium screen above the input circuitry (Of course, I may have added that due to an earlier poor-screening experience - it's all too long ago to remember).

'jnt

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