Using X-lock to stabilize PLL osc??

[N2PD]

I've had my K2 #58xx for quite a few years now, but have recently added the KPA 100 amp.  I would like to improve the frequency stability.  I have read EVERYTHING on the internet about this subject, and have now been experimenting with the PLL frequency compensation board, changing the RA value, with mixed results.  Here's my question...I see that the compensation unit varies the voltage applied to the varistors with changing temperature.  I am wondering if it would be feasible to replace that unit with one of the huff puff type stabilizers like the x-lock or K4DPK stabilizer that samples the output of the oscillator and applies a correction voltage based on frequency shift. Anyone tried this?

[vk2rq]

How much of the drift you are observing is due to the PLL synthesizer, and how much is due to BFO drift?73, Matt VK2RQ

    _____________________________
From: N2PD <[hidden email]>
Sent: mardi, novembre 24, 2015 2:21 AM
Subject: [Elecraft] Using X-lock to stabilize PLL osc??
To:  <[hidden email]>


I've had my K2 #58xx for quite a few years now, but have recently added the
KPA 100 amp.  I would like to improve the frequency stability.  I have read
EVERYTHING on the internet about this subject, and have now been
experimenting with the PLL frequency compensation board, changing the RA
value, with mixed results.  Here's my question...I see that the compensation
unit varies the voltage applied to the varistors with changing temperature.
I am wondering if it would be feasible to replace that unit with one of the
huff puff type stabilizers like the x-lock or K4DPK stabilizer that samples
the output of the oscillator and applies a correction voltage based on
frequency shift. Anyone tried this?



-----
Paul, N2PD
--
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[N2PD]

It does appear that there is significant drift in the BFO.  I'm going to make more exact measurements.  It seems to me that I read an old post from Wayne or Eric (when they announced the BFO mod) that said they would be experimenting with N750 caps in the BFO, but never saw anything about the results.  Perhaps I will go that route and try to stabilize the BFO first.  Maybe between that and careful selection of RA on the thermistor board (to stabilize the PLL) I can achieve some improvement.  Just a note...the rig doesn't drift excessively and is probably within spec, but there is room for improvement

[N2PD]

Well, I made some measurements tonite.  Using the k2 counter to track the BFO and an external counter to track the PLL, I measured from cold start to 45 minutes, with no transmitting.  The results:
PLL drifted 50hz UP, and the BFO drifted 60 hz DOWN.  Perfect for the higher bands where they almost cancel, but not so for the lower bands where they add (do I have that right?).
Does anyone have any info on frequency compensating the oscillators using negative coefficient caps?