I read in sci.electronics.design that Reg Edwards
wrote (in
et.com) about 'Measuring radiation resistance', on Mon, 8 Dec 2003:

If the wire end-to-end resistance of a 40m, 14-gauge dipole is, say,
2.76 ohms then -


Aerial efficiency = 100 * 140 / ( 140 + 2.76 ) = 98.0 percent.


Which is very good, isn't it? It's equivalent to 1/68th of an S-unit
which cannot be detected even by using a magnifying glass and the bloody
needle stands still for long enough.


Which also serves to illustrate how VERY uncrtical are aerial impedance
measurements.

Reg,
The OP is working with very non-ideal antennas, for which the radiation
resistance is probably only an ohm or two, and he wants to know if it's
0.5 ohms or 5 ohms, for obvious reasons. I don't suppose there is any
realistic way of measuring it, and modelling may be extremely difficult
if the antenna shape is not simple.

I've seen antenna evaluation does on 1:10 and 1:20 scale models, but we
don't know what frequencies the OP is using, so even that may not be
practicable, but if it is, one could work back from field strength
measurements to radiation resistance, with a big pad between the
transmitter and the antenna to 'soak up' the mismatch.
--
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
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