[TenTec] Omni VI Freq calibration

[Ken Brown]

> 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