SSB Grounding

[Fr J Hackett]

Sorry to be a bore on the subject but is it really nessesary to use 2" copper strip to attatch the ATU to the boats counterpoise. I am using a dynaplate because the boat is GRP and has an encapsulated keel ie no keel bolts. I am assuming that people are advising using a copper strip because it increases the surface area of the ground plate and connection, which seems logical if you are constructing the ground plane within the boat. I ask the question because it is proving difficult to locate a copper strip, all those I have located are only 0.005mm thick and expensive, the alternatives seem to be perhaps to cut up an old hot water cylinder, open and flatten a large pipe, use copper braid or simply connect with good quality wire. Whats the definitive answer apart from trying each in turn.

 

[jerryat]

Hi Pete,

You do not need thickness. Most professional installations use 3" (75mm) wide x 0.005" thick copper tape because it produces the best link to a sintered plate or keel bolt. What you are after is area since this forms part of the aerial in effect by groundind the 'other half' of the aerial to the sea. Not completely technically correct, but near enough for these purposes.

In a thread on here a few days ago, I mentioned that I'd bought mine from West Marine in the States, and I think that's an option still worth looking at. The cost when I bought mine was less than half the UK cost, but it was some time ago. It took about 5 days to arrive.

I bought a 50 foot length so that when the installed length corroded (and sooner or later it does) I had plenty to replace it with. Just done precisely that as it happens.

As you are using a sintered plate, probably the least effective way to achieve a good counterpoise (despite what the manufacturers say!) I would certainly use the correct foil (tape) to give you the best possible set-up.

All IMHO of course.

 

[Bergman]

The reason that people recommend tape is because of what is termed skin effect.

This is an effect where RF currents flow along the skin of a material rather than being evenly distributed throughout the section.

There are alternatives to tape, one being the outer conductor of coax, similar tro how you can use it for the feedwire to the backstay.
If you don't fancy the sintered plate there are alternatives.

One is to connect to the encapsulated ballast and rely on there being sufficient capacitance to the sea to work as an earth, depends on thickness of fibreglass, but usually OK.

Another way is to use an area of copper mesh stuck to inside of hull below the waterline.

Never used one of those sintered plates so can't comment from experience but reports seem varied.

 

[snowleopard]

It is essential to use strip rather than wire. The sintered plates do work but though they have a large wetted surface area, they aren't all that effective compared to a keel or copper mesh inside the hull. My setup has 2" tape and a 12" x 3" sintered block and is nothing like as powerful as other boats using the same set and ATU. I plan to switch to 4" tape and add some mesh on the inside of the hull.

 

[trouville]

i have an old large sintered plate thats now quite smooth in comparison with my new one? do they wear out,or shouldent i have used a wire brush to clean it each year?

Ive lost my link to a site that with the name of the boat you get the call ?

Im still sure that if there was a retired? cruser living aboard a maratime net would be wonderful--just as there is in the USA imagin the help it would be to know where to anchor to eat to shop and which ports are popular but not full for winter and to pass on emails from an account set up for messages that can be read over the air

Id love to put my SSB back on board but just listening around theres no point yet pity!

 

[Benbow]

[ QUOTE ]
........ is it really nessesary to use 2" copper strip to attatch the ATU to the boats counterpoise..

[/ QUOTE ]

yes

[ QUOTE ]
........ it is proving difficult to locate a copper strip..........

[/ QUOTE ]

Copper strip 50mm x 0.6mm £4/meter from this mob

 

[Birdseye]

The back stay aerial is a Marconi type using the sea as an earth system. In this system, the efficiency of the aerial is directly related to the resistance of the path to earth, and the shorter the aerial is in relation to the wavelength of the signal, the worse this problem is.

I cannot see any technical reason why a strip would be better than any other particular shape of the same surface area. In fact I would have thought that multi strand copper wire of the same cross section wopuld be better since it has a bigger ratio of surface area to cross section.

Probably what is more crucial is the size and surface of the plate below the hull. But the whole area is one for experimentation to find the best set up for your boat. On mine I could detect no difference between radiation when the plate was connected or there was no earth at all. Completely against all theory and I never found out why!

To summarise, you cant lose by having a good connector from the set to earth (sea water) but I wouldnt pay through the nose for strip copper as opposed to wire or even just flattened copper central heating pipe.

 

[Benbow]

[ QUOTE ]
I cannot see any technical reason why a strip would be better than any other particular shape of the same surface area. In fact I would have thought that multi strand copper wire of the same cross section wopuld be better since it has a bigger ratio of surface area to cross section.

[/ QUOTE ]

If you mean a circular cross-section bundle, then no it is far less effective than a flat strip because the skin effect mentioned above makes it little better than a solid bar.


[ QUOTE ]
On mine I could detect no difference between radiation when the plate was connected or there was no earth at all. Completely against all theory and I never found out why!

[/ QUOTE ]

How did you measure the radiation ? But anyway, a strip laid along the bottom can be very effective by itself because it couples to sea almost as effectively as if it was outside the hull.

[ QUOTE ]
but I wouldnt pay through the nose for strip copper as opposed to wire or even just flattened copper central heating pipe.

[/ QUOTE ]

I would ! and I would not call £4/metre paying through the nose.

 

[jerryat]

Tee hee! I don't think you'll change 'em Benbow! /forums/images/graemlins/wink.gif

Anyone who'll pay several hundred pounds for a transceiver, ATU and the rest, then begrudge 20 pounds worth of copper tape isn't gonna be persuaded here I reckon!! /forums/images/graemlins/crazy.gif /forums/images/graemlins/crazy.gif

 

[William_H]

I would suggest that the use of copper tape is not essential at all. Aluminium would also be adequate as is braided wire or even multiple strands of insulated wire. The length of the earthing wire will dictate how critical the earthing wire is so keep it short. ( especially as related to aerial length)
Perceived radio reception is on a logarythmic scale so your 100 watt transmitter may only effectively get 10 watts out but that difference will not be very perceptable at the far end perhaps only under most difficult conditions.
If the aerial Tuning Unit tunes correctly with a low Voltage Standing Wave ratio then the transmitted poower must be going out. but where too? Some will be inside the boat depending on the length of aerial wire inside and the length of the earthing wire. if it is a F/g boat it hopefully will still get out. What you want is the radiation out at a lowish angle to the horizon. This is best served by most of the power radiating from the backstay.
So while copper strip is good it doesn't mean other forms of earthing wire are not. If you can't get strip don't stress just use whatever you have and duplicate it if you have doubts. Certainly this area is not a clear science. olewill

 

[Ships_Cat]

It depends on the installation. The problem is nothing to do with current carrying capacity of conductors with small surface area as some claim (after all wire antennas and the internal conductor of coaxial cable are usually just bits of thin wire, aren't they?).

Lengths of wire can be inductive and at RF frequencies inductance impedes current carrying capacity. For wire to become seriously inductive at MF/HF frequencies it has to be in not very straight runs and reasonably long (for example, a bought inductor for electronics purposes is just a long bit of wire rolled up and it may have so much inductance that it blocks all MF/HF).

Wide flat strip with a big width to thickness ratio is less inclined to be inductive even when not in straight runs - again, it is not surface area that is the main concern, it is a shape thing, not a surface area thing and the wider the better.

So if the run is straight, and especially if short, then a piece of wire is fine. If the run is longer and only has a few gentle bends, then again a piece of wire will be fine with increased diameter reducing the inductance. In these cases I defy anyone to be able to subjectively identify any difference in signal strength compared to if flat strip was used. On my own boat the distance from antenna tuner to the earth is only about 18 inches and it would probably be poor practice to use anything but wire.

But if the run is longish and has right angle bends in it then tape is best advised. As others have pointed out the shield stripped from coaxial cable (the RG8 or larger size) and flattened makes a fair substitute but only if the run is not very long. However, it is subject to corrosion in the marine environment.

Tape has the added advantage in that when run to a keel or whatever in the bilge, it will capacitively couple to the sea outside both increasing and distributing the effective grounding area available.

So, from my own point of view, if I was to run a conductor from the ATU under a backstay to a keel, I would certainly use tape. However if the run was shorter, say to a grounding plate or mesh in/on the fibreglass close to the stern of the boat, or immediately to the hull if that is metal (as in my own case), then I would use wire.

I understand that some Cat 1 inspectors for the Offshore Special Regulations in some countries are demanding tape always for ssb installations (they don't understand radio) - so if the boat is a race boat, then it may pay to check their requirement.

John

 

[Benbow]

I don't disagree with anything said by the last 2 posters.

However, my answer to the question: is it really nessesary to use 2" copper strip to attatch the ATU to the boats counterpoise, essentially remains yes!

OK, of course Al is almost as good, after all most boat antenna are stainless steel not Cu. But copper is marginally better and readily available.

Of course you can get away with wire on a very short run, in fact look inside your ATU and you will probably see you are attaching to a length of narrow copper braid.

But in practice why use anything other than Cu strip for a run of more han a few inches ? It is avaialble and optimal (short of a steel hull or a mesh in your GRP hull) and as has been said several times, by coupling through the hull it effectively shortens the run and picks-up the perfect ground.

 

[Fr J Hackett]

Many thanks for all the replies, I have now found a source of 1 &2mm copper sheet coupled with the tape at £4 / meter, my first ground plane is going to be approximatly 6 sq foot of copper sheet inside the hull connected to the atu by tape. if that gives poor results then I will insall an external dynaplate. My understanding that the RF ground plane needs to exceed the surface area of the antenna which for a 7mm backstay will be about 0.2sq M, hence the size of the copper plate which will be difficult to install but seems to offer the simplest solution. It is not particularly the cost that irritates me but the thought of wasting money on something (dynaplate) that will not work particularly well and also the thought of following a long and well trodden path when it could be done correctly first time around. Once again many thanks to all I will let the forum know how it all went in due course.