The OCXO is the reference for all bands. As to individual bands,
there's a crystal {10 of them total} being one for each band. The
crystal oscillator is supposed to be locked to the precision reference
by a PLL. It may be that the PLL and varactor diode is not able to
pull the crystal on frequency. All of this is on the Xtal Osc. - L.O
Mixer Board.
Yes the band selecting crystal oscillators are supposed to be locked to
the OCXO. If they go out of lock they do not stop producing a signal, so
the radio will still work, but be off frequency. In that case there will
typically be a warbling character to received signals as the oscillator
is trying to lock up to the reference.
I have noted the absolute frequency will vary from band to band by a
few Hz. And unless the BFO frequencies are not absolutely correct, you
may find a slight frequency discrepancy from mode to mode.
Yes you really should compare the zero beat dial setting of USB versus
LSB on some stable carrier. If the dial readout is not equal for LSB and
USB when adjusted for zero beat then at least one of your BFO
frequencies is incorrect. (note that you need to adjust PBT to allow a
zero beat frequency to pass through the second IF, and even the 9 MHz IF
filter should attenuate a zero beat signal significantly, so hearing a
zero beat signal is tricky.) If you use a known frequency carrier such
as WWV to compare USB and LSB, you still cannot be certain if either of
the BFO frequencies is correct, because an incorrect BFO frequency can
be (incorrectly) compensated for with an improperly adjusted OCXO.
The BFO frequencies are best adjusted using a frequency counter that has
an accurate timebase.
DE N6KB
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