[Elecraft] K2 Freq. Stability

[Douglas Furton]

Hello, all

I've been bothered with the CW tone/filter setting
on my K2 for some time now.  I seem to need to run
CAL FIL daily, at least to have the BFO freq. read
into memory.  I observe that the CW tone starts low
and drifts upwards as the rig warms up when I tune a
signal to the center of the filters (maxing the
S-meter).

Here is some data characterizing the freq. drift
in my K2 (#6761).  I measured the PLL and BFO freqs
with a nice frequency counter.  I measured these
shifts with the K2 locked at 7050 kHz, and computed
the total shift = dPLL - dBFO (all referred back to
the initial (T=18.5C) measurements.  I measured the
temp. with a thermocouple in contact with the PLL
thermistor board. I also measured the  PLL and BFO 
control voltages at various times and found them 
to be constant.


	Cumulative freq. Shifts
T	PLL	BFO	Total 
(C)	(Hz)	(Hz)	(Hz)
18.5	0	0	0
19.3	9	-17	26
19.6	13	-34	47
20.2	17	-57	74
20.8	19	-70	89
21.3	24	-79	103
21.6	26	-87	113
22.0	28	-92	120
23.3	37	-124	161
24.0	40	-136	176
24.5	46	-164	210
25.0	53	-205	258
25.5	62	-256	318
25.5	70	-310	380

(I hope the table above remains tabulated
properly.  Best viewed with a monospace
font.)

It seems the thermistor board compensates the PLL
fairly well (although maybe I could tweak RA upwards 
a bit), but the BFO drifts considerably, and
since the PLL and BFO drift in opposite directions, 
the total drift is exaggerated.

I may measure the drift on a second band, but these
data are just from 40 m.  

I would really like to improve the temp. stability
of my K2.

Does anyone have any suggestions?

Thanks,

Doug Furton
K8EXB

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