Knowing the headphone grounding keys the transmitter is good, but please note:
"Plugging anything (even a bare 3/32" 3 conductor plug) into the jack fires up transmit."
I'm talking a ***bare 3 conductor plug***. Nothing is connected, nothing is grounded. Even ohmed out the plug to make sure there were no internal shorts (and that would be a first for me!) That's what was so surprising. I had inserted the plug so as to later establish whether tip or first ring was audio, and upon insertion, the thing keyed up. Not even a meter connected to the thing.
FWIW, this unit is a Moto MR350R 'Talkabout'. Tried another unit, and it behaves in exactly the same fashion.
I have a couple of earbud-lapel units ordered that should be here on Wednesday. I'll see how those behave, and if necessary, cut them open to see what in the devil they've done. My primary concern is whether I'll find internal switching on the 3/32" jack that is going to switch from the internal mic to the (non-existent) external one in any case. If they're doing that, then I'll have to go in search of (perhaps) some older Midland units that had separate 1/8" jacks for mic and audio out. I'm not crazy about those because they forget prior settings (like channel and privacy tone!) when batteries are removed.
WinRadio 1550, Alinco DJ X2/TE, Pro-2096, Pro-197
Last edited by ecanderson; 02-03-2013 at 9:38 PM..