VHF ground connecte to 12V negative?

[Lake-Effect]

Originally Posted by maddmike

This seems to be what's happening in my VHF and AIS. It also seems wrong because it creates a ground loop and, as others mention above, means DC negative current can flow through unexpected paths.

Ground loops aren't much of a problem on a boat; DC doesn't care, and the loops are usually too big to have predictable effect at SSB and VHF frequencies. But of course, unexpected paths can be a problem.

My chartplotter and autopilot have their case grounds isolated from the 12V circuit, which is what seems the right way to build it.

Are you certain about that? Have you checked those for continuity to confirm? In a perfect world, sure - case grounds would always be separate and separately bonded.

For DC radios with unbalanced antenna connections, it's common that the case is connected to the outer (shield) of the antenna connection, and to 12v negative.

[goboatingnow]

European boats do not ground negative to mast and other misc metals.

My mast is grounded to seawater via the keel it’s not connected to dc negative

[hzcruiser]

Originally Posted by goboatingnow

European boats do not ground negative to mast and other misc metals.

My mast is grounded to seawater via the keel it’s not connected to dc negative

Do you have a whip on your mast top? All whips, being unbalanced wires, use the coax shield as the other leg of the VHF signal. The PL259 connectors outer part connects to the bracket and the mast. If you use an insulated bracket or holder your emission will be hampered massively, IOW, not many stations will receive you.

Then your mast is connected to the keel, ok. On the radio side, the coax shell might also be connected to minus or it has a separate GND pin/screw/plug.

Hence your mast is connected to battery minus via that, unless you have measured it and confirmed it's not. Then it's most likely that you have a better radio with separate ant ground and bat minus lugs.