[Elecraft] crystal filter pitch differences

[Ron D'Eau Claire]

Tom  km4cu wrote:

Hello to all. First time posting herem glad to be a part of the Elecraft
family. I have a K1, K2, xg-1. the K2 is having a problem with pitch
differences, one bfo setting to another, the hard part is that sometimes
it's perfect, other times not. Normally if there is a pitch difference,
opt-1 is different. I have tried several times to get it correct but no
success. I have used Spectrogram also.. Any suggestions??


------------------------------------------

Is it a new K2 Tom? (Or at least with a s/n >3000). 

Some pitch variation is normal. The digital circuits that reset the BFO
frequency to that set up during CAL FIL have a resolution, or accuracy, that
allows perhaps 20 or 30 Hz. However, it is generally stable from day to day.


Older K2's had a BFO that drifted more than the current ones. The BFO, like
any oscillator designed to change frequency, tries to change frequency on
its own, usually in response to temperature changes. You may be experiencing
some BFO drift if the degree if change when stepping through the filters
varies from time to time. The drift issue with the older K2's was cured with
a mod kit from Elecraft. 

The normal method of reducing the filter-to-filter variation to the minimum
possible - assuming no BFO drift - is to force the K2 logic to re-read the
BFO frequencies. You do that by putting the calibrator probe in the BFO test
point like you did when running spectrogram, go into CAL FIL, and then
change each BFO frequency setting to and different value, then put it back
where it was. That movement causes the logic to re-read the BFO frequency
and store a new, hopefully more accurate, value in memory. 

One thing to keep in mind is that you can *not* "tweak" the frequencies in
CAL FIL while listening to a signal on the air. Only have noise in the
bandpass. That's because the BFO and Local Oscillator (PLL Oscillator)
frequencies interact to make changing the BFO frequency appear to make the
I.F. bandpass move. There a good write-up on that on the Elecraft web site
called "The Mechanics Behind CAL FIL". 

Ron AC7AC

-