The shield of the coax is connected to battery negative back at the VHF. If stray current is an issue, there may be a bad ground at the base of the mast. The plastic shim idea can work for this. There are such things as DC blocks for coax, but I cannot seem to find them with PL259 connectors. GMDSS certified 24 volt radios for ships I think have DC blocks built in to avoid this kind of thing, but the cost is quite high.
Do you have an issue yourself or are you just worried about it? I have to say I only ever worried about this with aluminum boats, but that doesn’t mean it can’t happen to you. I would think grounding the base of the mast back to the DC ground bus would put all the metal at the same potential. The mast already should have a heavy wire to a keel bolt. Joe Della Barba Coquina C&C 35 MK I Kent Island MD USA From: CHARLES SCHEAFFER via CnC-List <cnc-list@cnc-list.com> Sent: Friday, May 27, 2022 3:42 PM To: CNC boat owners, cnc-list <cnc-list@cnc-list.com> Cc: CHARLES SCHEAFFER <cscheaf...@comcast.net> Subject: Stus-List insulating VHF antenna mount Hey guys, Someone here at my boatyard said he had stray current from the VHF antenna until he isolated the bracker from the mast. I googled it but didn't find easy answers. Anybody ever hear of this problem? I can fab a plastic shim for the bracket but how do you isolate metal screws from the metal mast? Chuck Scheaffer, Resolute, 1989 C&C 34R, Annapolis
