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On Sat, 30 Jul 2005 06:12:33 GMT, Me wrote:
In article .com, "Skip Gundlach" wrote: As further background, we have full rails, with the gates combined electrically with brass straps belowdecks, attached to the arch, the pushpit and pulpit. We have about 110 lineal feet of 1" SS tube rail, unless you count the inner rails, plus the arch. In addition we have the standard 4" copper strapping leading to a sintered bronze Guest plane below the boat, and also connected to a 3x5' plate under the workbench top. I think we have a reasonably good ground. You will never know if you have a "reasonably good ground", unless you get yourself an Impedance Bridge, and check it at the frequencies that you commonly work. Anything that is more than 12" away from the water, isn't going to add "diddley-squat" toward building a Low Impedance Wideband RF Ground System, /// If you got a Plastic Hull, you are NEVER going to get a Real RF Ground, UNLESS the hull builder was smart, (they never are) and put 200+ Sq Ft of screen under the gellcoat down by the keel. Cellulose hulls are just as bad, and harder to retrofit that Plastic ones. Like I said in my first reply, Autotuners were invented to allow any "Dufus" to think he install an MF/HF Marine Radio System, and save himself all that money he would have paid a Compitant Radioman.//// Me Hehe...why don't you tell us what you really think, anonymous poster? If it takes 200 sq ft of screen under a gel coat to make a good RF ground, then folks who attempt a similar feat through a hull would need about 0.5 / 0.05 X 200 sq ft of material - That's 2000 sq ft of foil or metal mesh (for a 0.05 in gelcoat, and a mere 0.5 inch hull thickness) Now THAT would be quite a trick - a square about 100 ft by 20 ft. Better not tell the folks who use an antenna coupled through a 1/4 inch glass shield - a coupler that can measure 1.5 inch square. Admitted, this is often for FM radio (say 90 MHz) as opposed to 3MHz (?) on hf. Using these numbers for comparison, 90/3 X 0.5/0.25 X 2.25 sq in = 135 sq in of ground plane, hmmmm that's 1 sq foot in round numbers. Now that *does* look small to me. I expect the truth lies somewhere between 1 sq ft and 2000 sq ft. through a half inch hull section. There! How mealy-mouthed is THAT! :-) OK, let's get serious: how about locating a bronze through hull, and connecting a copper foil externally in contact with it. a square foot THERE, connected internally with good Litz wire might make a serviceable ground.... Brian Whatcott Altus p.s A hint for you: talking about "compitant radiomen" makes prospective customers nervous! :-) |
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