In article ,
Ed wrote:

We have 2M packet node transceivers at a new government radio site. The
new site owner requires isolators be installed on all transmitters. As you
might surmise, it doesn't seem possible to do so on a simplex one RF port
radio such an Alinco DR-135.

Anyone out there with some realistic suggestions on how we might manage
to do this?

You could probably do this with an isolator, a pair of SPDT coaxial
relays, and some modifications to the PTT circuitry between the rig
and the TNC.

You'd install the SPDT relays between the radio and the antenna.
Between the "normally closed" switchable ports, install a coaxial
number. Between the "normally open" ports, connect the isolator.

Take the PTT signal coming out of the TNC, and feed it to a bit of
circuitry (possibly analog, possibly discrete digital, possibly a
little 8-pin PIC micro). The effect of this circuitry would be detect
PTT from the TNC, drive a signal to the relays to switch them "on",
delay about 10 milliseconds (long enough for the relays to switch, and
stop bouncing), and then feed PTT to the radio. When PTT from the TNC
is deasserted, drop PTT to the radio immediately, wait around 10
milliseconds, and then turn off the relays.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
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