On Sat, 11 Nov 2006 12:06:16 -0000, "David" nospam@nospam wrote:

What would you define RF ground as? There seem to be a lot of different
ideas.

Hi David,

This is another instance of scale matters. Ground is meant to imply
an infinite resource of charge with no impedance to its flow.

Of course, "infinite" and "no impedance" are factors that are the
first casualties when RF is added as a requirment. This is from the
simple consequence of scale, because distance causes phase shifts and
brings impedance. A long wire that is perfectly capable as a ground
lead for 60 Hz can become a liability to short wavelength RF. That
wire (that we call ground) may connect to an infinite resource of
charge (the proper ground), but that charge can't get to the other end
because of possibly infinite impedances [again, infinite is in the eye
of the creator].

If you can contrive to make that lead to ground half a wavelength long
to the RF of your interest, that wire ceases to offer impedance and
acts much as you would demand of a ground wire. Curiosly enough, it
will never be zero impedance because it qualifies as a radiator (the
paradox of ground) which adds the loss of radiation. For most
purposes, however, it may be your only choice and you live with it.

Now, when we get to the actual mud of ground, and how well it performs
as an infinite resource of charge, RF still brings problems of scale
because that mud will also exhibit impedances correlated to wavelength
(corrected for velocity factors) that disconnect it from the total
earth's resource for infinite charge. This is why you lay down
radials (which simply increases coverage, but never completely escapes
the scale of wavelenght problem).

Moral to this tale:
Put your source (transmitter) as close to the mud as possible;
lay out as much copper as you can from that point to suit
a broader range of frequencies.

Alternative moral:
Put your source (transmitter) as far from the mud as possible;
Use a dipole and insure there are no connections to ground
whatever. Any violation of this last rule brings grief.
Such violations are legion and few escape.

73's
Richard Clark, KB7QHC