Hi Steve,
Well, I suppose I would consider using another buffered crystal oscillator
ONLY for the CW offset. Then add a buffered stage to the existing circuit.
Finally, use a damn-fast transistor to switch between the two buffered
outputs. Here, the two oscillators are freely running and never get shocked
with the extra capacitance that's now required to produce the offset.
In large production quantities, I can't imagine the change adding more than
$5 to $10 to implement, provided there's adequate real estate on the circuit
board to make the change. What do you think?
-Paul, W9AC
-----Original Message-----
From: Steve Ellington <n4lq@iglou.com>
To: tentec@contesting.com <tentec@contesting.com>
To: <tentec@contesting.com>
Date: Tuesday, January 05, 1999 4:49 PM
Subject: [TenTec] Omni VI chirp comment
>
>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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>
>
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