In article ,
Brian Whatcott wrote:
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! :-)
Nice thought Brian.... However what you seem to forget is that
capacative couping at RF Frequencies, is determined by three things.
1. Area of the Inside the hull Plate.
2. Distance between the two Plates.
3. Conductivity of the Sea Water Plate.
A 200 Sq Ft Screen in the cabin overhead isn't near (Orders of magnitude)
big enough to be an RF Ground for a MF/HF Antenna System, by itself.
Being located far (relative in capactive terms) from the other plate
(Salt water) means that the Rf couping into the water is what, can you
guess? Less than a few Picofarads. Now calculate the RF Impedance for
such a system at ANY, and All MF/HF Marine Frequencies that you like to
use, if you have enough computer power in your supercomputer. then come
back and explain it all to the rest of the world.
Me
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