[NautiG]

That is normal behavior for a non functioning antenna. It takes very little energy and antenna to receive, but much more antenna and power to transmit.

I'd recommend getting a fiberglass deck level antenna as a backup antenna for your vhf, and fix your mast antenna. I'd bet you'd get a good response to radio checks when you connect the fiberglass deck antenna to the vhf. The problem with the mast antenna sounds like a corroded cable, connections, or antenna.

I don't know anything about splitting an antenna between an FM and vhf radio, but that may be an issue too.

Scott
Gemini Catamaran Split Decision

 

[NautiG]

My suggestion to get a second antenna was not just about safety, but also to problem solve your radio problem. Connect the new antenna to the radio with a short piece of cable. If the radio transmits properly, then you have determined that the problem is not the radio. Connect the antenna to the cable at the base of the mast. If the radio transmits properly, then you have determined that the problem is not the splitter. Connect the antenna at the top of the mast. If the radio transmits, then you have determined that the problem is not the in mast wiring.

I'm not sure what you are trying to accomplish by determining the impedance or resistance, but then again I'm not an electrician, and about the only thing I use my multimeter for is to check voltage. I'm just describing the problem solving process I would use on my boat, if I had your problem.

Scott
Gemini Catamaran Split Decision