Bert Hyman wrote:

You appear to be posting from the US, so I thought I'd mention that if
this transmitter is an unlicensed "Part 15 Intentional Radiator"

This is a legal device. You can find them at Comtek (www.comtek.com).

I'm just trying to replace the antenna system they are using, which is
a lapel mic with about 48" of shielded cable between the 1/2" connector
and the mic head, with a fixed, shorter high-gain (rubber ducky type)
antenna.

Can anyone help me to accomplish this? What do I need in terms of
the antenna... the exact type?

Thanks.