[Elecraft] Re: BFO drift

[James Hammons]

      I have tried removing one of the BFO crystals and it did not
work.  Neither crystal would come down to the needed 4913.0.  I think
that this can't be done with crystals as supplied because they are
calibrated at the series resonate frequency and won't go down to this
frequency at zero volts without two crystals. Changing C174 only
increases the frequency by the way.  A crystal about 800 hz lower,
might work but it would be at the edge of working or not.=20
      Keep in mind that reported drift among K2's varied a lot with
some users reporting no drift of the BFO.   You can't really know
whether you are improving your K2 unless you actually measure the
drift.  From what I have seen I would guess that If your range, you
wrote it down about the middle column 2 page 57 is near the low end of
the acceptable 11.5khz range removing X1 or X2 will not help your K2
and it already is low in VFO drift.  If your range is near the top
25kHz, mine was 22.91 then removing the crystal helps a lot.
      The BFO drift would be about 50Hz in the worst examples and that
just isn't enough to cause loss of signal out of the passband.   What
we are talking about is drift from a cold start.  In actual use after
30 minutes to an hour the temperature stabilizes and the drift is only
about 1/4 of the warm up drift.=20
       Back in the good old days a VFO was good if it only drifted
about 30ppm per degree C. and hams were happy to use them.  My K2
drifts about 1/60 of that.   That doesn't mean that I won't try to get
it to zero drift, but that's no reason to bad mouth the design.  The
K2 is truly remarkable for what it is.  A small, lightweight, low
power drain, CW/SSB transceiver with a world class receiver in kit
form.  To top it off, a moderate price. =20