> Doug,
>
> The BFO is obviously the culprit here.
> What serial number is this K2?
> Do you have the new L33? with many turns of #36 wire. If this is an
> older K2, install the BFO upgrade kit.
> If you already have the upgraded parts, then I suggest you equip
> yourself with all of the parts in the BFO circuit and just replace
> them. You can replace them one at a time until you find things more
> stable, but I believe it is easier to replace them wholesale and see
> what happens. You will need
> 2 BFO crystals X3 and X4
> C173 and C174
> D37 and D38
> L33
> Replacing L33 will require a high value 1/8 watt resistor to mount the
> toroid - the K2 lists this as R116 PN E500086.
>
> 73,
> Don W3FPR
>
> Douglas Furton wrote:
>
>> 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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