[Elecraft] K2: Freq stabilization heatup time?

[Ron D'Eau Claire]

Yes. The K2 BFO is an xtal oscillator which needs some warm-up time to
stabilize. There's only one BFO, but it's frequency is shifted (it's a VXO
circuit) as needed for the various filters. That ability to shift its
frequency also reduces the stability a bit. 

The K2 also uses a hybrid synthesizer approach for main VFO that shifts the
frequency of a xtal oscillator over a limited range, then the synthesizer
jumps to the next range, and so on. Again, the fact that it uses a variable
frequency crystal oscillator means it can drift more than a fixed frequency
crystal oscillator. 

On some bands the drift of the two oscillators can work to make the apparent
frequency drift worse than on other bands but the 20 minutes the manual
recommends should be more than enough for it to stabilize. Even so, you can
detect some drift, typically in the tens of Hz, if the K2 is exposed to
really extreme temperatures such as leaving it sitting in the direct sun,
etc.

If you have an old K2 there may be some stability mods you can add. The
drift issues turned up after the KPA100 100 watt amplifier module was
introduced because it heated the interior of the K2 enough to make them
apparent. 

Considerable work was done to improve the oscillator stability of both the
main tuning synthesizer reference oscillator and the BFO. Those changes were
incorporated in the later K2 production boards. They included replacing some
parts and adding a thermister-based temperature compensation circuit for the
main VXO.  

Also, there was a small issue with the tuning control encoder in which
putting it in exactly the "wrong" position could cause the synthesizer to be
confused and shift the frequency unintentionally. That was corrected in
firmware. 

If you do have an old K2, you'll find kits of parts available from Elecraft
to upgrade your unit. If your K2 has the latest circuits, you can still make
a few custom changes to the temperature compensation circuit to "fine tune"
your particular unit. That involves changing the value of a resistor. 

Those mods are described on the Elecraft under Builder Resources. One list
of mods is:

http://www.qslnet.de/member/la3za/K2/mod3000.html

Ron AC7AC




-----Original Message-----
Hey Gang,
It appears to me that the K2 has a BFO stabilization heat-up time.
The other day, I got the impression that all four BFO (F1 - F4) were
drifting write after power up.
Or is this my imagination?
-- 
 Bw_dw at fastmail.net

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