[TenTec] Omni VI warbling sound

Peter Bertini radioconnection at gmail.com
Wed Dec 26 09:15:59 EST 2018

That warbling   can also be caused by a HFO crystal that is trying to phase
lock to the master oscillator. The PLL will sweep the oscillator loop
voltage trying to achieve a locked condition.

I've had problems with a few (three) of my Omni VI rigs developing problems
with the oscillators on the 81595 LO Mixer Board. If the problem is not in
your VFO PLL,  look at the lock signal on Pin 11 of U13 on the CPU board.
It should be a very narrow negative pulse (100 MHz scope, fastest scan
rate) and stable.  Oscillators are adjusted for minimal pulse width.  If an
oscillator is out of lock, you will see a lot of jitter on pin 11.

If anyone who has found a cure for this issue I'd appreciate hearing from
you. It appears to be heat related, as the crystals age the board becomes
very heat sensitive, and the board is in encased in what is basically an
oven which adds to the problem.


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