Has anybody performed the TX EN mod on their Omni 6/6+ that fixes the
qsk keying loop issue with Acom amplifiers? The instructions for the
Paragon are up on the Acom Yahoo Group files section or viewable at
http://n1eu.com/TXENmod.doc
Barry,
Are you dead-set on using the handshake method (TX OUT/TX EN lines) between
the 6+ and ACOM? On the 6/6+, be careful about using the TX OUT/TX EN when
keying a non Ten Tec amp. I participated in a discussion here back in the
late '90s where some folks were advocating use of an RCA "Y" adapter,
together with a 1N914 steering diode to key an external amp. That method
results in hot switching of the trailing RF envelope. I confirmed this back
in 1999 with my Alpha and ACOM amps when observing the keyed envelope on a
scope. In fact, I burned out the RJ-1 vacuum relay in my 77Dx as a result
of this configuration, des[pite the fact that the amp should protect against
hot-switching. No matter what solution you decide to use, absolutely
confirm the non-presence of RF envelope hot-switching.
My solution?
On the ACOM and Alpha amps, it's not necessary to invoke a full handshake
and yet obtain super-fast keying that is not subject to hot-switching. To
accomplish this, seek out Ten Tec's "T" voltage bus. This bus carries the
proper timing for use with fast external amps. Next, find the base resistor
that feeds the Omni's ext. amp relay's switching transistor. Lift the
base-bias resistor and connect it to the "T" bus. Finally, cut the
switching transistor's collector going to the relay coil and bring the open
collector directly out to the Omni's ext. amp key jack. You may need to go
into the Omni's menu and deactivate the relay since the switching transistor
is now controlled from the "T' bus. In this configuration, the jumper is
palced back between TX OUT and TX EN and I've never seen indication of
hot-swithcing at any keying speed..
Paul, W9AC
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