Although Paul's contributions concerning the 2.8khz crystal have been
helpful, let me issue a concern of mine.
The chirp seems to originate in the BFO of the tx-audio board. I spent
nearly 3 months verifying this both in the shack and on the air. You can
verify this easily by simply listening to your 9mhz signal on another
receiver as you key the Omni VI. Use a hank of wire for the receiver's
antenna and just jam it inside the Omni's cabinet through the vent holes
on the left side of the rig. You will hear the actual signal from the BFO
before filtering. If you doubt this, simply remove the filter then listen
to it.
I've done this test with 2 Omni VI's here in the shack. Now switch to the
FSK mode, retune the reciever and listen to the difference. This is how it
should sound.
Correct me if I"m wrong here but I beleive in the Omni VI, when you key
the rig, you are not only starting the LSB oscillator from dead zero but
also switching a capacitor across it's crystal to shift it's frequency.
This is really asking a lot of an oscillator! I believe the old Corsairs,
Tritons etc just switched in the capacitor across the already running
oscillator resulting in a fairly clean signal. In the Omni VI, I believe
this is what happens in FSK mode, just a capacitor switched across an
xtal.
I'm operating from memory with no schematic so check me out on this.
For you who want to hear what you sound like without that 2.4khz filter,
just yank it out and stick a 100pf capacitor between the input and output
holes. If it sounds the same then don't expect the 2.8khz xtal to help.
Next question.
If the 2.4khz xtal is really the cause of all this, why can't the cw ops
just yank it out, bypass it and leave it that way? SSB ops who do
occasional cw would have more to contend with of course. Perhaps a diode
switching system could bypass the xtal during ssb operation.
My guess is: It will still chirp.
BTW: I even tried ordering a coulple of extra 9mhz xtals from TT in hopes
one didn't chirp.
Steve Ellington N4LQ
N4LQ@IGLOU.COM
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