On Mon, 08 Dec 2003 00:55:46 +0000, Paul Burridge
wrote:

|
|Hi guys,
|
|How does one go about measuring (with a reasonable degree of
|accuracy) the radiation resistance of antennas? And when I say
|"antennas" I mean any radiator from a balanced dipole through to a
|random length of wet string with a damp matchbox for a ground plane.
|Must it be done with a noise bridge or is there another way that
|requires no special test equipment (aside from a scope/sig.gen etc.).
|I'm primarily interested in checking out highly *non*-ideal antennas
|for use in non-ideal situations/locations.

This was best posted to rec.radio.amateur.antennas but...

For ordinary wire antennas operated independent of ground and without
loading coils, the radiation resistance is very close to the resistive
part of the feedpoint impedance. Any number of instruments can
measure this with reasonable accuracy. A noise bridge or some of the
popular impedance bridges (AEA CIA, MFJ, etc) can do it.

If the antenna has loading coils, or is operated against ground, then
the losses in those (sometimes greatly) affect the measurement.

In either case, "special" equipment in the sense that it's more than a
scope and signal generator *is* required. Very often transmission
lines are a part of the equation and their effects need to be
accounted for as well.

I suspect that the more non-ideal the antenna, the more difficult the
measurement.

Wes N7WS