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Catalina/Capri 25/250 Sailor's Forums

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VHF antenna ground

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glivs
Admiral

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USA
836 Posts

Initially Posted - 03/29/2014 : 07:28:00

Have you grounded your VHF antenna, and if so how? I'm looking at new radios which all seem to have a dedicated connection on the back for this purpose. A quick look on-line, simply states 'do not connect to your DC ground system as this may cause interference' (paraphrased).

Gerry Livingston, Malletts Bay, VT
"Great Escape" 1989 C-25 SR/WK #5972

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britinusa
Web Editor

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USA
5404 Posts

Response Posted - 03/29/2014 : 11:12:53

No. (Don't have a cable that long

)

DC -ve is already connected. So no need for grounding on our boats unless the boat has Lightening Protection installed.

Paul

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Voyager
Master Marine Consultant

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5397 Posts

Response Posted - 03/29/2014 : 11:17:20

On a boat, especially in freshwater, there really is no ground. You have battery + and - terminals (neither of which is a ground) and if you have 110 VAC shore power, you will have hot, neutral and ground. Many boats will have a grounding system - a bus bar for AC ground. Do not connect your DC negative to the AC ground.

Some boats have a bus bar bonded to a grounding plate - about a 12"x12" copper plate - that's connected through the hull to AC ground or just for grounding the mast and rigging to the water.

There are several schools of thought about DC grounding, AC grounding, grounding plates and lightning grounding that I will not address here. My advice is NOT to ground AC to a hull ground plate, the keel or the water in a freshwater lake. Could be deadly.

VHF radios and antennas are intended to work just fine without a DC ground. Think about a hand-held - no ground. I would connect your switched, fused battery + to the + terminal on the radio and your battery - to the - terminal of the radio. Full stop.

Sources of VHF interference:
1. Certain older Dr LEDs can create RF hash on the radio. Replace them.
2. The outboard spark plugs can create telltale pops
3. The ripple current from your alternator can create whine on your VHF transmissions.
The main problem with VHF interference is not that you cannot receive clear signals, but that you produce a noisy outbound signal, or you distort the digital DSC signal and cause data errors (i.e.: bad data).

It always pays to check your own radio output by asking someone on your boat to transmit while you stand on another boat or the dock and listen on your handheld to the quality of your sound with all the lights on and engine running.
Ask your partner to rev the motor to listen for engine noise.

To check your DSC signal, you can send a test signal to the boat patrol or Coast Guard. Check the radio's manual on that.

In many locations, BoatUS also operates an automated Radio Check service on Ch24 or Ch28. It will record your transmitted signal and replay your transmitted signal and add an advertisement or promo You can hear your full transmit and receive loop this way.

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glivs
Admiral

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USA
836 Posts

Response Posted - 03/30/2014 : 06:33:52

I'm not talking about power. Yes the DC system and the VHF ground are two separate systems. Apologies also in that in my first post I misinterpreted the VHF ground as an antenna ground. My question arises from the following taken, for example, from an ICOM VHF manual: "Connect to a vessel ground to prevent electrical shocks and interference from other equipment...". I assume it refers to the grounding system that both Paul and Voyager refer to (e.g., copper plate) but was curious if anyone had followed through when installing their VHF.

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Voyager
Master Marine Consultant

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5397 Posts

Response Posted - 03/30/2014 : 15:43:22

Do you have shore power? If so, I would keep the VHF completely electrically isolated from AC ground. This prevents any stray AC current feeding back through the VHF. If no shore power, it's a non-issue as far as I can tell. Unless you have an inverter connected to your 12VDC system, it's not possible to be electrocuted by a 12V battery.

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glivs
Admiral

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USA
836 Posts

Response Posted - 03/31/2014 : 16:24:41

Bruce....appreciate the input but I agree this is a non-issue. For the record...we are on a mooring so no access to AC.

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Voyager
Master Marine Consultant

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5397 Posts

Response Posted - 03/31/2014 : 19:17:44

Yep, so don't sweat it. Just over complicating something that should be simple.

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The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.