Lumpy wrote:

Regarding this antenna for the low power transmitter,
I expect there will be a bit of grief coupling a rubber duck, or anything else, in place of what
was the mic cable.

Are they somehow using the shield of the cable as the antenna? If so it's likely floating and
not directly connected to circuit ground. Plugging a duck in place of the mic, with typical connectors
and adaptors, would likely not connect the antenna element to the "antenna terminal" of the device.

Thanks, Lumpy. Now we're getting somewhere.

Yes, they are using the mic cable shield for the antenna. Cable is 48"
long with a 1/8" phone plug on the end. The shield side of the mic
connector is floating, that is correct.

I would be connecting the antenna to a new socket of some sort. A BNC
if I can make that fit this rather smallish casing.

Can you give me any starting point for the antenna itself? If I was to
connect it to the existing lead off the coil, the one that now goes to
the mic shield... remove if from there and connect it to the center pin
on the antenna. Would the outer ring of the BNC go to battery negative
ground?

The manufacturer mentioned using a 5K resistor on each side as I recall.
Does thie affect the gain in any way?