Mike,
I don't have any measurement data to support it, but I do believe that the
oscillators (BFO, PLL, VCO) can be influenced by temperature and the
proximity of objects to the frequency determining components - the
difference should be slight, but could account for 10 to 30 Hz in the end.
Also, remember that CAL FIL must be run to for the results to be correct.
Even if the filters are already correct, each BFO must be moved a notch and
then moved back for the new values to be written. Failure to do that will
look like your calibration efforts 'just didn't work right'.
You are correct in saying that once the values are written into EEPROM, the
reference oscillator is out of the picture - but those values only represent
voltages which SHOULD produce a specific frequency - if the conditions
around the frequency determining components of the oscillator are not the
same as when the values were written, the resulting frequency may be a bit
different.
Now, I must admit that the differences are slight - but for those who would
struggle to get things 'right on', you should realize that these factors
will influence your results.
73,
Don W3FPR
----- Original Message -----
Not really an issue. Get C22 right with the cover off and right away do
the "cal pll" before putting the cover on. After that it doesn't matter
what happens when the cover is replaced 'cos it has no effect whatsoever
on calibration.
Regards,
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