Earthing VHF Radio

[SimonFa]

I have had complaints that there is a lot of background noise and distortion from my VHF radio. This was reported on CH16 and CH80, I didn't test the rest.

I have had the radio tested and that's all OK. The antenna system has been VSWR tested and is OK.

The only thing I can find that is possibly wrong is that the earth terminal on the back of the radio has never been connected, or at least I can't find a connection. I have checked for continuity between the antenna outer and the earth cable to the keel and its open circuit. I've tested else where and no connection.

I suspect it is an earth problem because it appears to be worse when the GPS and other instruments are on.

Should the VHF radio be earthed? I'd have thought so just from a safety point if not RF screening but from my apprenticeship days I'm sure that the radio should be earthed.

Anyone got any thoughts or experience?

Thanks,

Simon

 

[rob2]

I suspect that very few marine VHF sets are earthed, its not usual on a DC system. Some may have negative earth bonding to shore power, but that is irrelevant once the boat leaves her mooring. My understanding is that the earth connection on the set is to accomodate some designs of antenna which use an earth plate to make the sea a ground plane for transmission purposes.

Good to hear that your VSWR reading is good/acceptable, but whilst that is the first useful test of an antenna system it doesn't show up quite a number of faults. Often, having checked the VSWR, the only further investigation is "does it work?". Probably the next test is to try your VHF set on another boat's antenna which is known to be good. If that eliminates the problem, then the most cost effective cure is to install a whole new antenna and feeder cable!

Rob.

 

[lw395]

I have had complaints that there is a lot of background noise and distortion from my VHF radio. This was reported on CH16 and CH80, I didn't test the rest.

I have had the radio tested and that's all OK. The antenna system has been VSWR tested and is OK.

The only thing I can find that is possibly wrong is that the earth terminal on the back of the radio has never been connected, or at least I can't find a connection. I have checked for continuity between the antenna outer and the earth cable to the keel and its open circuit. I've tested else where and no connection.

I suspect it is an earth problem because it appears to be worse when the GPS and other instruments are on.

Should the VHF radio be earthed? I'd have thought so just from a safety point if not RF screening but from my apprenticeship days I'm sure that the radio should be earthed.

Anyone got any thoughts or experience?

Thanks,

Simon

I would suspect supply-borne interference.
I would guess that the case/chassis of the VHF is connected to the -ve of 12V supply? If not, you could try connecting it.
You could try adding some capacitors across the 12V supply, close to the radio, or a ferrite of some sort in series with the +ve.
Is there a data connection from the GPS to the radio?
If so, try disconnecting it and see if the noise goes.

 

[salar]

You can buy ferrite rings by the handful on eBay, worth adding these on all nearby power cords. My Garmin VHF has an earth, just connect what may look like a spare screw on the metal case or heat sink to the boat Ground.

 

[rogerthebodger]

I had some background noise on my VHF due to my PWM solar regulator injecting noise when the batteries charge is such that the PWN regulator starts reducing the current.

 

[lpdsn]

Should the VHF radio be earthed? I'd have thought so just from a safety point if not RF screening but from my apprenticeship days I'm sure that the radio should be earthed.

Anyone got any thoughts or experience?

I earthed mine. It's connected to existing earth wiring which is connected to the keel - also have a GI between that and the shorepower earth. Works well, but I don't know if it would've worked just as well without the earth. I also have ferrites. Ditto, whether they've made a difference or not.

An alternative is to wire it straight to the negative of the battery to bypass any other circuits with noise. A lot of boats have that, but far more people seem to think it has something to do with bypassing unreliable switches (that are otherwise pretty reliable) rather than earthing noise.

 

[SimonFa]

I suspect that very few marine VHF sets are earthed, its not usual on a DC system. Some may have negative earth bonding to shore power, but that is irrelevant once the boat leaves her mooring. My understanding is that the earth connection on the set is to accomodate some designs of antenna which use an earth plate to make the sea a ground plane for transmission purposes.

Good to hear that your VSWR reading is good/acceptable, but whilst that is the first useful test of an antenna system it doesn't show up quite a number of faults. Often, having checked the VSWR, the only further investigation is "does it work?". Probably the next test is to try your VHF set on another boat's antenna which is known to be good. If that eliminates the problem, then the most cost effective cure is to install a whole new antenna and feeder cable!

Rob.

I'm fairly confident about the antenna system. From Weymouth I pick up Brixham and Solent without any problems. But trying it on another boat is a good idea, thanks.

I would suspect supply-borne interference.
I would guess that the case/chassis of the VHF is connected to the -ve of 12V supply? If not, you could try connecting it.
You could try adding some capacitors across the 12V supply, close to the radio, or a ferrite of some sort in series with the +ve.
Is there a data connection from the GPS to the radio?
If so, try disconnecting it and see if the noise goes.

The chassis isn't connected to the -12v rail, I tested it to a nearby buzz bar. I was wondering if that was safe but I suspect it is.

Good point about the data connector, its only two open twisted wires, and the ferrite beads. Again something to try.


And thanks for the other replies so far they are all useful if if not mentioned here..

Simon

 

[pampas]

cured my noise by running both +&- separate from any other cable and as far away from any instrument as possible.

 

[William_H]

I presume OP is talking about reported noise and distortion on the transmission. It is possible as has been suggested that it is interference coming into the radio via the battery supply wires. However one might expect that this would give noise and interference on receive as well. Thsi kind of probblem can be isolated by trying the radio and a fully separate battery. If that cures the problem then try moving the wiring and fitting ferrite and capcitive filters.
However I wonder if it is just on transmission if there is a problem with the microphone and its wiring. You say the radio (and mic) were checked. I also wonder if OP is not simply taking too loud or the mic is too sensitive causing distortion on voice.
The trick is to get a helper to listen on a hand held on an unused channel and try to get an idea of what the problem is.
No earthing and antenna are unlikely to cause noise and distortion. No VHF radios are not usually earthed separately like an HF SSB radio. This is becuase the antenna and groundplane are integral at 5the end of the antenna cable and the cable provides the earth to the groundplane.
good luck olewill