Chris wrote:
I have a VHF radio connected to an antenna on the mast,
which does not make a sound. It has power, the lights on
it come on, but not a sound on any channel.

I suspect that the cable leading to the antenna is bad,
disconnected, or whatever. (Does this sound like the likely
cause?)

To check this, what do I have to measure in antenna/cable:
Impedance? What does an ok antenna cable show?

Thanks!

A spare, portable antennae is quite common since the masthead antennae
is vulnerable to a number of mishaps; I carry a suction cup version.
This could be a good time to invest, or you should be able to find
someone that has one. Another possibility is a signal strength meter.