Jon, thanks very much for your thoughtful review.
On disabling transmit mode: Some transceivers have a hardware
switch on the outside of the box that will disable transmit. Others have a software
switch that you need to run a configuration program for. I am not positive, but I think all of them have a way to stop transmitting while still receiving--and more likely this capability will be in a newer unit than an older one.
I THINK there is actually a capability in the specs for Port Control in a harbor to be able to turn off transmit by broadcasting a code--maybe only for Class B? (not sure where I read this, so don't quote me on this part).
MilltechMarine.com has user's guides and stuff for the units they sell, checking the guide (or email
Milltech) would be the best way to confirm for a particular unit.