isolating VHF antenna bracket from mast

[CHARLES SCHEAFFER]

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

[Blair Clark]

Hmmm not sure about this. Will be interested to hear other thoughts.

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[Ben Sutton]

The only way I know to isolate screws from the mast is the use of lanacote on the threads. This normally done to help prevent galvanic action from the dissimilar metals.  Whether that will do the trick in this case I don’t know.

Ben Sutton

Evangeline C&C 34+ 1990

On May 28, 2022, at 1:22 PM, Blair Clark <blairc...@gmail.com> wrote:

Hmmm not sure about this. Will be interested to hear other thoughts.

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[Matt Cowan]

The shield connection on the antenna wire is usually grounded to the radio’s (and the boat’s) electrical ground. Often this electrical ground is tied through to the mast, keel, engine etc. If this is the case isolating the antenna bracket from the mast would make no difference. 

I just measured mine - from the shield of the coax wire (at the radio) to the mast ground is less than 0.5 ohms and the voltage on 25w transmit is less than .001 volt - indication of no stray current opportunity. 

My conclusion is that it makes no sense to isolate the bracket from the mast. 

https://casualnavigation.com/does-a-vhf-antenna-need-to-be-grounded/

This article talks about grounding vhf antennas and indicates that you may even get better performance on an antenna that doesn’t normally require a ground plane. 

Matt

Stargazer XX

Anchored off Beausoleil Island in Georgian Bay (water temp 12 degrees C)

Matt Cowan ETC

519-590-1191

On May 28, 2022, at 4:22 PM, Blair Clark <blairc...@gmail.com> wrote:

Hmmm not sure about this. Will be interested to hear other thoughts.

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