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RE: Icom 910H - external relay control

Hi Bart,

I took a look at the schematic, and believe that the only transmit control
signals at the accessory jacks are inputs to the radio, not outputs that can
control anything.  Internally, the "PTT" and "Send" signals are actually
diode isolated pull-down circuits that ultimately go to the radio's
computer.  I recommend that if you are keying the radio with the mike, that
you try putting an interface between the mike and the radio.  Something like
the MFJ-1272 TNC switchbox would make the connection available easily
without modifying the radio.  The mike plugs into the 1272 and then it in
turn plugs into the radio.  Inside, it has not only the switching that would
control a TNC, but the connections to the PTT line are available.  It would
be easy to bring them out for use in a transistor-to-relay controller.  You
are interested in the push-to-talk line (pin 5) at the microphone jack.  I
believe I saw the 1272 in the most recent AES catalog for about $25 on
closeout.  Apparently, a lot of hams are going to soundcard TNC
implementations, so they aren't selling many of the TNC interface units.

Alternately, if you are keying the radio via the Accessory jack (at pin 3),
or the Data1 jack (also at pin 3), you could take the control signal from
that point.  Note that they are isolated from the microphone jack PTT line
and each other by diodes.  None of these connections at the radio are meant
as outputs, and only accept pull-down (grounding) at their terminals.

Well, that's my two-cents, for what it's worth....  I'm in the middle of
trying to come up with a sequencer that will take a key-down from my
microphone OR from the computer (I like the digital modes) and intervene,
preventing the radio from pushing RF up the coax until the antenna relays
have had a chance to route it around the preamp.  That's how I know that the
microphone and data/accessory connections are isolated (made that
mistake...).  Either one will key the radio immediately, if given the
chance; and, the preamp will be toast.

Best of luck!  Let me know how you work it out.  I may end up with the
craving for more RF to the antenna, too, when I'm ready to try WSJT.

73' de Dan, KB4L

-----Original Message-----
From: owner-AMSAT-BB@AMSAT.Org [mailto:owner-AMSAT-BB@AMSAT.Org]On Behalf Of
Jahnke, Bart, W9JJ
Sent: Monday, August 26, 2002 9:09 AM
To: amsat-bb@AMSAT.Org
Subject: [amsat-bb] Icom 910H - external relay control

Gang, anyone out there have a source for a mod (add on) to control an
external relay (to control external KW amplifier bypass relays) using the IC


--Bart W9JJ

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