"Doug" wrote in
nk.net:

By the way, the MFJ unit has been a real jewel to sweep those top of
the line VHF marine antennas with built in filters for RFI from land
mobile public safety frequencies. We have customers who have areas on
the Columbia River where police and fire departments just blast
through on a lot of the cheaper radios. The SEA 156 was the old
solution for them as it had a great receiver that was immune to the IF
image/front end over load problems. The customer does not like the SEA
157 front panel operation and we are currently testing other brands
now on a few of their tug boats. The antennas


I use a single hi-split DB Products cavity with two slugs in it as a
bandpass cavity between the VHF marine radio and the antenna. Passing the
signal through the cavity has two benefits....
1 - No paging/fire/cop/taxicab/etc. interference breaking the squelch...
2 - The radio isn't connected to the antenna, physically, and if you ground
the cavity to the ship's grounding system it keeps the lightning and static
discharges out of the marine VHF....