[Elecraft] K2 XFIL Oddity

[John, KI6WX]

Joe;
The frequency shift between XFIL settings is a complicated interaction
between a number of parts in the K2.  The PLL reference DAC is 12 bits and
limits the VFO tuning steps to ~10 Hz on 10 meters to ~5 Hz on 40 meters.
The BFO DAC is 8 bits and causes the BFO tuning to take ~20-30 Hz steps.
The firmware compensates for these effects, but I believe the firmware only
reads the VFO and BFO frequencies to 10 Hz (Wayne; correct me if I am wrong
on this).  Finally, the BFO and VFO oscillators drift with temperature and
time.  This means that the frequency compensation for the current operating
conditions will differ from the original calibration.

There is a way to reduce this effect.  Perform both a CAL PLL and then a CAL
FIL for all filter settings and modes just before you start operating.  This
will reduce the error between the XFIL settings for your current operating
temperature.

Installing both the BFO and PLL stability mods will reduce the effect of
temperature changes on the various XFIL settings.  These changes are very
worthwhile for any K2 that is operated in an environment in which the
temperature changes by more than a few degrees.

-John
 KI6WX

----- Original Message ----- 
From: "Joe P" <jplan@jeffnet.org>


> I've noticed that as I switch between the different XFIL settings on my
> K2 (#3490), the pitch of the received signal seems to change sometimes.
>   The maximum change seems to be about 10Hz, small but clearly audible
> (and clearly visible on Spectrogram.)  On any given frequency, there
> will always be a pair of adjacent filter settings where the pitch shift
> is greatest, but the particular pair of settings will be different for
> different areas of a band.  For example, at the bottom end of 40m, it
> seems like the greatest change happens when switching from FL1 (1.5kHz)
> to FL2 (0.7kHz).  At the top end, it's when switching from FL4 (0.2kHz)
> to FL1 (1.5kHz).
>
> It's really a minor thing but it seems a little odd. Is it normal?  Is
> there something I can do to improve the situation?
>
> Thanks in advance.
>
> 73
> Joe
> KB8AP