Fred McKenzie wrote:
I also posted the question over on rec.radio.amateur.equipment, and
received an answer there. It seems that the UT-121 to IC-9100 interface
is very poor. It uses a micro-miniature connector, and uses sticky-foam
to hold the little PCB in place. The cure for the problem is to
repeatedly re-install the module until the transmitter will un-key when
you let up on the microphone button.

After getting it to work, several people have told me, "Everybody knows
that. It is a common problem!"

At the price that 9100 is sold, should we expect any quality?