[Elecraft] KX3 frequency stability with DC supply voltage variations

[Lance Collister, W7GJ]

I recently took my KX3 with me on a 6m EME DXpedition to operate as V6M and I did 
have some problems with the stability of the AC line when I keyed my amp.   I don't 
know whether that might have also caused variation in the output from 12 VDC supply 
powering the KX3, but some people did report a "drifting problem" during my 
transmissions.   I didn't see any indication of frequency drift during receive (when 
the rig would be cooling down from a transmit cycle), so I am curious to learn if the 
KX3 might be vulnerable to changes in DC supply voltage.   Has anyone experimented 
with this or do you know whether the KX3 has good internal voltage regulation? If it 
is a problem, I may have to get a different switching power supply that is more 
stable under large AC input voltage swings.

The actual stability on JT65A mode I think was fine, at least it seemed to be stable 
enough on receive.   Upon further investigation, I think many of the reports about 
people not being able to decode my JT65A signal were due not to instability of the 
KX3, but simply the fact that my signal was too weak to decode when I was replying to 
someone else.  I have added a pair of external heat sinks and gone through the 
temperature compensation routine, and believe that those steps were adequate:

http://www.bigskyspaces.com/w7gj/KX3HeatSinks.htm

I would really like to be able to continue to take the KX3 with me on 6m EME 
DXpeditions, because it has so many great features and is so compact.   However, I am 
also tempted to buy another K3 just to take on DXpeditions, since I know stability 
has never been in question with my K3 field operations.

I look forward to any suggestions or insights anyone may be able to provide.    MNI 
TNX and VY 73, Lance

-- 
Lance Collister, W7GJ
(ex WA3GPL, WA1JXN, WA1JXN/C6A, ZF2OC/ZF8, E51SIX, 3D2LR, 5W0GJ, E6M, TX5K, KH8/W7GJ, V6M)
P.O. Box 73
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URL: http://www.bigskyspaces.com/w7gj
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2m DXCC #11/6m DXCC #815

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