SSB Ground Plane

[summerwind]

I am considering installing SSB and have been doing a bit of reading on the subject.

One of the pieces of equipment apparently required is a ground plane, apparently made of bronze which is somehow fitted to the hull (Below the water line?)

I have a steel boat. Would one of you wise men please advise if I would need to fit ground plane plates.

Thanks in advance for any help.

 

[romany123]

Summer
I have SSB on board, arial is an insulated backstay but no ground plate. I have had no trouble pickin up weather faxes from it.
Dave

Dave

 

[Roberto]

Lucky you, there is no need for a ground plate/foil whatever in a metal boat, the hull itself provides an excellent connection to seawater. Do not worry if external hull is covered with paint, epoxy or else, radio frequencies will easily pass through this sort of capacitor; just connect the ground terminal stub on the tuner to an exposed part of the hull.

Roberto, M0ITA

 

[30boat]

Receiving is one thing but for emiting you do need to ground the transmiter.

 

[romany123]

wouldent know mate I just use it for getting weather faxes

Dave

 

[HaraldS]

Not sure if you are talking about just receiving or also transmitting.

For receiving, both an isolated backstay or an actitive masttop antenna works very well. I have both and seem to get somewhat better results from the active antenna. The only draw back of a good active antenna (mine is from RR) is that you may get the pre-amp overloaded from a strong local signal. Never a problem at sea, but I was once anchored near a big AM radio station and it completely stuffed the active antenna, so I had to use the backstay to get my weather charts. You don't need more than the 'regular' ground for receiving.

For transmitting you need a good counter poise, which may be a good ground or it could be radials or both. On a steel boat, obtaining a good ground is easy and you just need to make sure you have a good ground connection from the transceiver or tuner to your hull. Best is to use a 4" wide copper foil, surface is what conducts HF, not cross section.

The normal advice for non mental hulls like mine is to tie as much metal masses in the boat together and connect a big surface ground plate, like dynaplate and if you can have copper foil laminated into the hull so that you get additional capacitive coupling to the water.

Some time ago I talked to one of the ham antenna celbrities how told me I can forget any ground if I used matched radials, and that they work much better than any real ground. I knew that, but didn't think this was practical on a boat, until he told me about his experiments.

You have probably seen radials on some VHF or CB antennas, they are the rods, (typically 4), that stand out horizontally at the foot of the antenna. They have to be matched to the wave length within a few percent to work properly, (such a counter poise is resonance based), so that you need different lengths for different frequency bands. Radials are one quarter of the wavelength.

The news was that these don't have to stick straight out in four directions, but he showed that you only loose very little performance if you make them zig-zag or fold back, as long as the foled back wires are some two inches away from the other. You also don't need to run away in all directions from the antenna foot, and less than the usual four radials also induces less degradation than one would expect. He recommeds two.

That boils down to running a few wires trhough your boat, matched to your most favorite frequencies. Off course wires for different frequencies can go along side.


2mhz = 117 feet can aslo be 62 feet
4mhz = 58 feet
6 = 39 feet
7 = 33 feet
8 = 29 feet (you can skip this one if you using ham 7mhz)
12 = 20 feet
14 = 17 feet
Just simply attach one or two of the above lengths to your tuner ground lug and sneak in the wires wherever you can.

I now have both, radials for three favorite frequencies for SSB e-mail, and a ground system with foil laminated into the hull etc. Have not tried it out yet, but will do so this summer and compare the two systems.

With your steel hull you should have a good general ground, and you might not want to fuss around with radials, but if you feel you get poor performance on certain freqeuncies, it's easy to just lay out the a matched wire on deck and see what change it makes.

 

[alant]

Got on a Halberg Rassy 45, which had just been fitted with a ground plate (stainless). However, the fitter had not sealed the hole thru the hull & subsequently when lifted back in, lots of water was getting into boat & in between inner/outer skins. Be warned.

 

[ean_p]

Harald
Is there any risk of electrolysis in the hull of a steel craft when the transmitter is in use???

 

[Bergman]

I take the point about tuned radialls as a ground plane, but does not seem really practical on a boat.

It is also worth pointing out that the ends of the radial wires are high voltage points and if the radials are truely resonant (as they should be to work) then there will be several thousand volts on them when transmitting.

This could cause 2 problems:

Firstly giving a severe burn to anyone who touched such a wire.

Secondly if the end of the radial were to touch a true earth (very easy on a steel boat) then there would be an immediate mismatch which would reflect a lot of power back into the transmitter causing it to shut down if internally protected or destroy the PA if not.

On a steel boat ONE good connection to the hull, foil is best, but thick wire will do. Make it as short as possible. Should work fine

 

[HaraldS]

Wouldn't worry about that.
Transmitt times are short and HF usually no problem. On the DC side I found that DC-power (12V) negative (or positive) are galvaically separated on both transceiver and tuner, so that no power supply current should run via the ground.

 

[johnsomerhausen]

You don't need a ground plane on a steel hull; the hull IS your ground plane. Just the shortest possible conductor (thick copper braid or foil) from the ground of your antenna tuner to the hull (or even your "pushpit" if it's welded to the hull). When I was net control of the South Atlantic Maritime Mobile network, I noticed that the best signals came from steel hulled boats.
john (N2ZOA ex CX4ACI)