[Elecraft] Rig drift

[George Anestis]

Hi Earl,

Your K2 sure does have a strange problem re: the filter passband drift.
I've taken a close look at mine with Spectrogram since reading your posts,
just to see if mine did anything like this.  I didn't think so, because I
never noticed anything by ear.  I can even use the most narrow filter
setting (100hz) when the rig is stone cold without any problem....the signal
still is centered where it should be.  Looking at Spectrogram confirms my
ears...the filters do not drift as yours does.

My K2 frequency appears to drift about 90 hz from cold start to normal
operating temp in a matter of 10 minutes or so.  Ambient temperature changes
also make it move around a bit, but I've never seen it go more than about +
or - 90 hz...for a total of 180hz.  During Field Day with the rig running
really HOT out in the sunshine, it was still not so far off to be annoyed by
it, and the filter passband position didn't appear to change at all in
relation to my sidetone frequency (out of curiosity I checked WWV
occasionally when the temps were very high).  Overall, the K2 (mine, anyway)
is closer to frequency AND more stable than an old but highly regarded
Collins 51j-2 tube receiver I had back in the '50's!!  My FT-1000mp with
TCXO is more accurate and more stable, but that's to be expected,
considering the greater $$$ involved.

This won't help you resolve your problem, I know, but I just wanted to give
a sanity check and let you know my results...all K2's definitely don't
behave as yours is doing and I believe you DO have a problem.  I wish I
could give you a clue where or what to look at, but I have no clue.  For
what it's worth, my K2 is 3 years old and has the solenoid inductor for L33
(I believe it is), rather than the toroid that is used in current K2's.  I
believe reports indicate the toroid version drifts more than the solenoid,
(so I can't see making that "update"!) but I don't think I've seen reports
that this relates to drifty filter passband symptoms.

Hope you find that bug and squash it!

73 - George - W3ANX   K2 #518

> Using the RIT or split has nothing to do with and doesn't "cure" the
> problem.  My transmit and receive frequencies are the same, no matter
> what the temperature is (I think!).
>
> The problem is drift (BFO or PLL, or a combination of both) where, if you
> use Spectrogram to look at a received signal at the pitch your SPOT is
> set at, the signal is outside of the filter passband when cold and drifts
> into the passband as the temperature increases (and drifts out the other
> side of the passband if the temperature continues to increase).  Using
> RIT has nothing to do with this.
>
> This problem has been also mentioned by others on this reflector.
>
> 73, de Earl, K6SE