Posted by
Ron D'Eau Claire-2 on
Jan 03, 2005; 11:48pm
URL: http://elecraft.85.s1.nabble.com/A-minor-C22-question-tp373225p373229.html
HOWARD W. ASHCRAFT, Jr. W1WF wrote:
Last night I redid my C22 reference oscillator adjustment using WWV on 10mhz
as the zero beat reference. This is the third time I have adjusted C22 and
each time I am able to adjust C22 to a precise offset balancing TP1 and TP2.
However, when I put the cover back on the K2/100 I find that WWV zero beats
a few tens of hz off. (After last night's adjustment, the zero beat was
10000.03) One should expect to be +- 10 hz as that is the finest resolution
of the VCO, but it would be nice to get a little closer.
--------------------------------------
You are probably fighting the resolution limits of the digital-to-analog
converters (DAC's) used to convert between the analog tuning voltages for
the BFO and PLL reference oscillator and the digital values stored in
memory. Since they convert the analog voltage into a binary number, and use
that binary number to recreate the voltage later as you tune in a signal and
choose the filter setting you want, they are never exact.
Sometimes one is closer than 10 or 20 Hz, sometimes not. At that level it's
a matter of "luck".
That's the source of often hearing a small step in the frequency of a CW
beat note when switching between filters too.
Ron AC7AC
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