Without specialized equipment you can not measure the impedance of your VHF
antenna.

A couple of alternatives a Disconnect the antenna coax from the radio
and substitute a length of bare wire about 18 inches long into the
connector. (Gauge of the wire is unimportant). Then try to communicate
with a nearby radio on the same channel.

The more elaborate alternative is to have a communications company use a
BIRD inline Watt Meter/SWR Bridge to analyze your antenna system. It is a
simple task and cost should be minimal.

Don Dando

Moast any ham radio operator will have an SWR bridge... Look for the
antennas on the boats...

denny