[Milsurplus] ] BC-221 question

[C Whitaker]

de WB2CPN             2005.03.06

It wasn't intended that the VFO in the BC-221
be stable.  That's what the Calibrate Knob is
for.  The crystal was expected to be stable, and
had a small variable capacitor for adjustment.
We used to power up the unit while it was outside
the box, put a long screwdriver into the little
capacitor slot, then wrap the whole thing in
bath towels etc in order to bring the temperatures
up to somewhere in the ball park.  Then adjust
the crystal harmonic to WWV or some other accurate
HF signal.  Most of the time when we used the
BC-221 it never got up to temperature anyway. Some
of the ones in airplanes were freezing.  The trick
was not to get the crystal exactly on frequency,
but to measure the error.  That was done by setting
the main dial close to the WWV frequency, do the
Calibrate operation, then set the dial to the listed
WWV frequency and note how far the BC-221 was off.

73  Clete