I post the following as a copy of a reply I made to the uk.amateur
radio newsgroup.

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I am considering the using some army surplus aluminium alloy poles
as
part of the rf ground for an inverted L antenna. They are thick
walled
4ft tubes able to withstand stand being driven into the ground, and
are
lying around waiting to be used for something.
The issues which come to mind are corrosion through contact with the
earth and electrolytic reaction where a copper cable is attatched
with
steel bolt and eylet connector.
Has anyone on here tried this?

John
m1jta
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John,
I have used 3 or 4 feet alumininium alloy tubes as earth rods, on and
off, for many years. I have found them just the same as any other or
metals - ie., no bloody good.

Electrically, at HF, a 3 or 4-feet earth rod is no better than a
single, thin, radial, shallow-buried, horizontal wire of the same
length which is much easier to install.

The resistance to ground has nothing whatsoever to do with the
conductivity of the metal or surface corrosion products. It has
everything to do with the resistivity of the soil in which the rod is
embedded. ie., the soil in the immediate vicinity of the rod.

Resistance to ground depends almost entirely on rod length and is only
very slightly dependent on rod diameter.

Only old wives believe resistance is related to surface area of the
rod or electrode and dig great holes in their back gardens to bury
unwanted, scrap, hot-water cylinders. They would do better by
approaching their local scrap metal merchant.

A 3 or 4 feet rod in typical garden soil has a resistance to ground of
the order of 100 to 200 ohms and by itself is useless.

To locate one rod immediately next to another does next to nothing
regarding ground connection resistance. A pair of rods must be spaced
apart by at least twice their length before the resulting ground
resistance approaches half the resistance of one rod.

A collection of a number of rods must be spaced apart by many times
greater than their depth of burial to obtain the full benefit of all
being connected in parallel.

Consequently, the connecting wires from rods to a focal point
themselves constitute a good system of shallow-buried radials and the
short rods at the ends of the radial wires can be dispensed with.
Exactly the same result can be achieved just by extending the radials
by another, insignificant 3 feet. The rods are both wasted effort and
wasted copper (or aluminium).
----
Reg, G4FGQ