I believe you are correct John. Rather than using the Omni's internal AMP
relay. a simple modification to the Omni's Control Board takes care of this:
1) Rather than use the Omni's AMP relay, use the preceding transistor driver
as an "open collector" to the Omni's RCA jack.
2) Next, lift the driver transistor's 10K bias resistor on the end away from
the transistor's base, and run a short jumper from the lifted end to the
Omni's "T" voltage line located just a few inches away from the transistor,
adjacent to a Molex header.
This creates the perfect timing sequence for the Alpha 87A and many other
amps. The Omni's "T" voltage is derived from a very complex, discrete
Schmidt-trigger circuit on an adjacent circuit board. An integrator is
formed prior to this circuitry and the final "T" voltage is derived from the
ramped CW ("T/R") waveform voltage. Thus, the voltage appearing at "T"
provides just enough time before and after the waveform edges to key a fast
switching transistor. The stock Omni transistor is Vce rated at
approximately +38 VDC so it works great with most any late-generation Alpha,
including my Alpha 87A. My Alpha PA-70V uses a +70V DC key line, so I did
make a change to a HV switching transistor just for this purpose.
-Paul, W9AC
Jacksonville, Florida
----- Original Message -----
From: John Brosnahan <broz@csn.net>
To: <amps@contesting.com>; <cq-contest@contesting.com>
Sent: Wednesday, April 07, 1999 1:37 AM
Subject: [AMPS] ? Omni VI and Alpha 87A in QSK ?
>
> I have been asked about using an Omni VI with an Alpha 87A.
> Suppossedly, rumor has it there are some issues with this
> combo when using QSK causing shortening the CW
> characters. It is my understanding that the relay line on
> the Omni VI returns to receive before the RF output stops.
>
> But this condition should be handled by the 87A OK
> because the PIN diode TR switch ANDs the drive
> RF signal with the relay signal to avoid just this type of
> mis-timing. In addition, the 87A has an alternative
> method of operation which allows the CW keyer
> to control the amp PIN T/R directly and then the AMP
> tells the exciter when to TX. And this should also
> work with the Omni VI's timing problem.
>
> I would like to hear about experiences from anyone
> who uses an Omni VI with an Alpha 87A on QSK CW.
> Your input may help a DX station! THANKS
>
> 73 John W0UN
>
>
>
>
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>
>
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