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Here's just a thought.  I recommend you go "upstream" of the radio - don't
make it do the work.  Install either a Microphone-TNC switch (e.g.,
MFJ-1272) giving you access to the keying signal; or use a desk mike, and
add a control lead to key your amp via a relay.  Your mike, not the radio,
would trigger it all.  The radio doesn't need to generate or even relay that
signal, just respond to it.  And the amp doesn't care where it comes from,
especially if it is remotely mounted at the masthead.

The MFJ-1272 has gotten cheaper with so many soundcard modems out there.
E-bay has them all the time.  I got one there, but use it with my old
MFJ-1278 TNC (a wonderful antique that keeps on running packet for me).

I control transmit via a simple homebrew mixer switch-box that accepts the
signals from my desk mike and selectively routes them to my IC-756Pro,
IC-910H, or IC-718.  I got the connectors on E-bay, and the box and switches
at Radio Shack.  I don't need to key or talk through more than one radio on
a band at a time.  This also gives me the option (not yet implemented) to
install a closed loop to the masthead to enable the keying only after the
masthead relays respond, ensuring no transmit power goes up the coax until
the preamp is out of circuit and grounded.  In effect, I plan to key the
masthead relays, and then use them to key the radio and amp.

Good luck with your project.

73' de Dan, KB4L

-----Original Message-----
From: owner-AMSAT-BB@amsat.org [mailto:owner-AMSAT-BB@amsat.org]On Behalf Of
Joe Steinmetz
Sent: Sunday, September 15, 2002 11:19 PM
To: amsat-bb@amsat.org
Subject: [amsat-bb] ICOM 910H


I own an IC-821H and would like to replace it with something than can do
23cm. I have been looking at the 910H. One of the issues I had with the
821H was that it did not have separate ground-on-transmit signals for
each band (like the Yaesu 736R does). It appears from the ICOM 910H
manual (available here
http://www.icomamerica.com/SUPPORT/DOCUMENTS/manuals/ic-910H.pdf ) that
this shortcoming (in my opinion) has not been corrected. To make things
worse I don't even see a single ground-on-transmit signal available (the
ACC and DATA sockets list PTT and SEND as inputs). While I can justify
not using an external linear for 2m and 70cm, 23cm is a different story.
I don't like to use RF sensed switching of linear amplifiers - I like to
use a ground-on-transmit signal from the radio. So, what am I missing?
How does one accomplish this with the 910H and an external 23cm linear
AMP without RF sensing?



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