Nigel;
I designed the PLL stability mod for Elecraft. The mod was designed to
compensate for the drift in the average PLL reference crystal. These
crystals do vary some by lot, and the drift can be further reduced by
adjusting the value of Ra as explained in the manual.
The drift will also vary by band, and you might want to measure your drift
on several bands. Don't assume that the drift will be worst on 10 meters.
My K2 actually shows its worst drift on 30 meters, and its lowest drift on
10 meters. The main reason for this is that the PLL reference stability
changes with its frequency.
>From the data you present, your drift is several Hertz per C. Tuning Ra can
reduce the drift to less than 1 Hz/C on the worst band. My K2 shows a
worst-case drift of 0.5 Hz/C measured from 10C to 50C. I tuned resistor Ra
to minimize the drift on all bands.
In your case, you do need to reduce the value of Ra. An initial
measurement using Ra at 27K would be a good start. You may find it
necessary to use 1% resistor values to get the lowest possible drift.
-John
KI6WX
----- Original Message -----
From: "Nigel" <
[hidden email]>
I want to fine tune the temp compensation by adjusting the resistor RA,
currently at 33k and would like to confirm my thinking before starting.
My K2/100 drifts down about 50Hz after 30 minutes from turn on and
stabilizes. After a good period of transmitting which gets the fan on high
it will drift down another 40 to 50Hz. The PLL range is 13.26kHz
The uncompensated oscillator drifts down with a temperature increase
therefore I need to further increase the compensation. To achieve this I
need to decrease the value of RA. Perhaps 27k or 22k? Have I got this
right?
73, Nigel ZL2DF
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