[Elecraft] K2 CAL_FIL and the BFO

[Ron D'Eau Claire]

-----Original Message-----
Hi Steve,
A wierd quirk on my part, is I fuss over my K2's Filter settings.
It took me about an hour, and a little home-brewed rock-solid signal
source, but I am able to get all 4 filters so that I can not hear any
shift at all in tone from one filter to the next.

I know I'm a strange bird
But hey, thats what turns me on :~]

Duane
N1BBR

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Don't be surprised if you do anything that requires you to re-read those
frequencies into memory again and you once again notice a small shift, even
though the BFO frequencies are identical to what you had before. That
doesn't mean there's anything wrong with your K2. 

That's because of the resolution of the A/D converters that "read" the BFO
frequency and convert it into digital data for storage in the K2's memory.
They don't have a 1 Hz resolution. In fact, IIRC, their resolution is 20 Hz.
So getting a "perfect" match between several filters is a matter luck,
having the A/D converter digital output accidentally hit exactly the right
values. 

You don't need an especially solid frequency source, just one that doesn't
drift in the time you step through the filters checking the frequencies.
Indeed, the easiest way to put the filters exactly where you want them is to
use a wide band noise source so you can see the entire filter bandpass with
a program like "Spectrogram" that provides a spectrum display of the audio
output. 

Ron AC7AC