Earth Plates

[Samphire]

Can anyone help re earth plates/ground plates for electronics.leaving aside SSB radios which need certain resistance etc my navtex and radar (both Furuno) require an earth and have worked ok using sea cocks as earths,but would a copper earth improve performance?

 

[ccscott49]

I don't have earths on either my radar or Navtex and they work fine. So I can't really help, but a sintered bronze earth plate would be my choice. I'm fitting one this year anyway for SSB.

 

[Aeolus_IV]

My only thought on what you've said is that using seacocks as earths run the risk of inducing corrosion unless all your seacocks are bonded together to an anode at some suitable localtion.

As for Radar and Navtex, I've not heard of anyone who has needed to provide an earthing route specifically for these devices.

I'm sure somebody will shoot me down now I've stuck my head above the parapit.

Jeff.

 

[jimboaw]

just redone my ground plane. Glassed in copper sheet 10 sq ft, from a roofing supplies place, on the inside of the hull. Bonded in all steel tanks, chain plates etc, etc with 3in copper foil. Works fine.

 

[ccscott49]

I suppose I could use my giant fuel tanks as a ground plane aswell, hadn't thought of that, (no way I can put copper sheet inside the hull). Then connect with copper foil to the radio, I wonder if that will be enough?

 

[Aeolus_IV]

I thought the whole point of a grounding plate was to make as good a connection as possible to earth (or in our case, water), and so should be on the outside of the hull. Am I wrong in thinking this?

Jeff.

 

[ccscott49]

Yes, it's not an earth plate to water as such, it's something to do with radiating the signal or somesuch. Not sure of the actual details. Too Ham for me.

 

[jimboaw]

Yes and No ! some modern glass boats have the ground plane for SSB bonded into the hull in the form of copper mesh. Its the area that counts. Your electrical earth should still go to an external fitting.

 

[ccscott49]

The electrical earth of what?

 

[Roberto]

There is no need for the HF ground plane to be actually in the water. If you have a plate inside the boat, under wl, then it will form a sort of capacitor with the water, the hull being the dielectric (material separating the two faces of the capacitor).

This is enough to couple the plate to ground.

 

[vyv_cox]

Instructions for my new radar state "if the vessel does not have a bonded ground, connect to battery negative". In my case the battery negative is connected to the engine that has a straight connection to the water via the prop shaft. No non-metallic flexible couplings to provide insulation.

 

[Aeolus_IV]

Ahh, that makes sense, area is then key aspect to give best result.

Jeff.

 

[Roberto]

I was talking about HF radios ground, ssb etc. Surely navtex (being receiver only) and possibly radar ground are much less demanding. For HF radios as well, sometimes a copper cable thrown in the sea from the tuner can be enough...
If you feel something is wrong, try adding copper foils between large metal lpates inside the hull (tanks, keel bolts, etc), and go on adding more surface only if still needed.

 

[billmacfarlane]

There used to be a product called a "Dyna-earth" , which was a copper plate which you through connected to your hull in the same way as an anode. It was basically a copper plate with lots of dimples which I think was to increase the earthing area. I had one fitted to my last boat to provide an earthing point for the Decca aerial. I don't know if the product is still avaiable.

 

[charles_reed]

Actually sintered gold-plated copper balls.

Alleged to give a vast effective RF surface area for a tiny plate.

I've got one and most radio hams reckon them a waste of time.

On your RF ground, the important thing is surface area, I've used plated copper mesh (available from RS Components) which is sold for screening video and sound cables - epoxied onto the inside of the hull underneath the aft cabin.

You're right SSB needs the most generous plane area, followed by radar, but all your radio gear needs connection to an RF earth, DGPS, Navtex, VHF, AM/FM radio, CD & cassette player.

 

[charles_reed]

Consider it shot off - no professional would install a real radar without an RF earth.
With teensy-weeny 2-3kW small boat stuff it's probably not lethal, just sloppy.

 

[charles_reed]

only works if it\'s below WL nm

nm

 

[charles_reed]

Not entirely - external groundplates are about 60% (I'm assured) more effective than in-hull bonded ones, but far more difficult to fit and keep clean and effective.

 

[charles_reed]

Sound advice nm

nm

 

[Aeolus_IV]

I knew it would happen .. but there seem to be conflicting views here. You seem to imply that, yes, a proper RF earth to ground is required - others say that a sheet on the inside of the hull, not earthed to ground is sufficient. Eh?

I undertand that proper, efficient transmittion of radio requires setting up some form of standing wave (of fractions there of) in the aerial, and that to do this one end (though the transmitter) must be grounded. For reception this isn't so important, but a good ground will allow you to pick up weaker signals.

I ask out of interest - the only transmitting device I've on boat is the VHF radio, can't see me find the space or power for a radar.

Jeff (Now, where did I place my head?).