[MRCA] GRC-109/T-784 "Voice" Design Challenge

MilComm Guy m38inmaine at gmail.com
Thu Oct 16 13:00:06 EDT 2025


I picked up a GRC-109 set at the Nearfest show this month, as I was walking
back to my truck with it Charlie mentioned how he had thought about a voice
mode modification and that it may not be too involved.  So I thought I
would toss out a design challenge here hoping the mil radio community here
will participate and come up with your design to add a voice mode circuit
for the T-784.

A few features necessary would be:
1 Fit in the available space inside
2 Non-invasive ie easily removable back to original configuration
3 Compatible with period correct microphone, T-17 or M-80 wired to a PJ-068
plug.

My contribution would be to make a bushing for the existing desiccant tube
hole to accept the jack for the PJ-068 plug, this way there are no extra
holes.

I know very little about radio circuits, I'm a nuts and bolts MV
restoration guy and have to rely on the seasoned experts here, of which
there are many.   If you would like to submit a design please do so here on
the reflector and start a discussion on it.  What's in it for you ?, I will
gladly pay for the parts and on your end satisfaction of a job well done.
I will also have a nice data plate made up with all the call signs of the
design entries, no call no problem initials will work.

A copy of the manual can be found here:
https://www.cryptomuseum.com/spy/rs1/files/TM_11-5820-474-14_19620518.pdf

I would also like to thank all the MRCA gang for all your help, without you
my mil radio hobby would not be possible, the knowledge and willingness to
help is greatly appreciated.
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Thanks
Mark
K1HF
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