Re: BIG counterpoise

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>



 > Original poster: "J. B. Weazle McCreath by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <weazle-at-hurontel.on.ca>
 >  >Original poster: "Gregory Peters by way of Terry Fritz
 >  >Where I live, the ground is pretty much solid metamorphic rocks,
 >  >Devonian/Carboniferous phyllite to be exact.  My house is cut
 >  >into a hill, so there's probably only a foot of topsoil at most.
 > I've got similar problems here...trying to dig into my soil is
 > like trying to push a nail through a board without a hammer!!
 >
 > Why not try a system of radials?  Ideally they should be one-
 > quarter wavelength long at your coil's operating frequency to
 > do it "by the book", but if you put in a dozen or so wires in
 > various directions and as long as possible, you should be OK.
 >
 > For my radial system I made a hub three inches in diameter of
 > several turns of bare number 14 wire and connected all of the
 > inner ends of the radial to the hub.  A much heavier lead then
 > connected the hub to the base of the secondary and any other
 > system components needing an R.F. ground.
 >

I wouldn't bother with the quarter wavelength thing: it's not like you're
trying to get a 50 ohm match, or have a perfectly omnidirectional radiation
pattern.  Concentrate on making the counterpoise the "other plate" of the
capacitor for the topload/secondary, which is what the "earth" does
normally.  Also, the counterpoise will have significant capacitance to
ground, which will be a fairly low impedance at RF, so you don't actually
need a ground rod.

Ground rods are primarily for DC and low frequency (i.e. mains frequency) to
insure that "common mode" voltages are reasonable. They also provide a path
(and a pretty darn poor one) for impulses, e.g. from lightning.

Classic 1/4 wave ground planes for antennas are designed to reduce IR/ground
losses and pattern problems, and have a different set of design criteria.
For broadcast band, one reason for an extensive radial network (i.e. per
recommendations in Brown, et.al.) is to make the "grounding" (and hence the
drive point impedance) of the radiator more consistent, and not so dependent
on whether it has just rained, etc. This kind of thing is important when
your FCC license requires you to feed your array of 5/8 wave masts in a
particular way to hit your designated market area.  For ham, HF kinds of
applications, (generally above 3.5 MHz) the resistive losses in the
partially conducting ground can really hit hard for a resonant vertical
antenna.