To: rsgb_lf_group@blacksheep.org
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From: N1BUG <paul@n1bug.com>
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Date: Fri, 29 Dec 2017 08:29:24 -0500
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Subject: Re: R: Re: LF: TXing 2200m WSPR
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Hi Markus,

> Could the scope "blurring " be caused 
> by a high-frequency rather than low-frequency oscillation?

It's possible but what I see is not what I would expect in that 
case. My experience has usually been that with a high frequency 
oscillation I see two sine waves: the fundamental and another with 
shorter period which is the HF oscillation. Here I don't usually see 
that. I see one sine wave keeping the same period but with amplitude 
"blur". No blur at the zero crossings, maximum blur at the positive 
and negative peaks.

That is what I see most often when it is misbehaving somewhat 
mildly. But sometimes I do see two "clean" sine waves with slightly 
different period. To me this suggests oscillation near the 
fundamental frequency. I can usually (but not always) make it switch 
from the single blurred since wave to two clean ones with different 
period by increasing bias or RF drive.

> Have you tried a 
> simple "snubber" network (e.g. 1 nF + 10 ohms) at the drain?

No, but I will try it next. I don't have any high power 10 ohm 
resistors, but I suppose if there is significant HF energy the 10 
ohm resistor burning up might be a clue. :-) I maybe could make a 
higher power 10 ohm resistor by putting a lot of chip capacitors in 
parallel, don't know what that would have for stray capacitance though.

Paul N1BUG