[R-390] Grounds

[K2CBY]

Other than for lightning protection (and that is a VITAL qualification),
there is nothing magical about an earth ground. A counterpoise 
works just as well so long as it is large enough relative to the 
frequency in use.

Think HF and Loran A antennas mounted on transport aircraft or bombers 
of the piston-engined era (a large, well-bonded, highly conductive 
ground plane).

Think also AM radio stations operating in rocky terrain or in 
the desert where the earth has about as much conductivity as 
glass. The only remedy there is an extensive array of ground 
radials.

Standard broadcast practice is to use radials ¼ wavelength long 
at the operating frequency (or an odd multiple of ¼ wavelength) so 
that the radial will present a low and almost entirely resistive 
impedance at the common point.

So far as the roof is concerned, I would be worried about bonding 
the galvanized steel panels together as enough places so that they 
would model an equipotential plane.  

I also assume that the antenna will be somewhere above the roof 
-- not 100 yards away from it. While it’s not going to affect the quality 
of the ground, the proximity of the antenna to an effective ground plane 
is certainly going to affect the antenna impedance and the radiation
pattern.

Miles, K2CBY

Miles B. Anderson, K2CBY
16 Round Pond Ln
Sag Harbor, NY 11963 USA
Tel.: (631) 725-4400
Fax: (631) 725-2223

E-mail: k2cby at optonline.net