[TowerTalk] Measuring radiation resistance of a vertical

[Tom Rauch]

> Is it possible to measure the radiation resistance (only)
of a vertical with
> either an antenna analyzer or some other type of readily
available piece of
> equipement?

Yes it is, but you probably cannot do it.

To measure radiation resistance you either have to know the
effective current causing radiation and the net power
radiated or you have to measure the impedance at a point in
the system and then shield the antenna in a large lossless
dome
and observe the change in resistance when the shield is in
place.

The converse of this is how do I measure the loss resistance
of
> the antenna?  I am trying to determine how effective my
radial system is and
> how efficient my antenna is.

http://www.w8ji.com/radiation_resistance.htm

The best way to measure anything is to measure what you want
to know as directly as possible. Radiation resistance will
NOT tell you efficiency
unless you somehow can manage to normalize all losses to the
point where radiation resistance is defined.

The only way to measure efficiency is to measure applied
power and net radiated field. That's pretty difficult.

The most effective thing you can do is to establish a good
reference antenna and compare the two. Most people can't do
that. What I would suggest is you change the ground system
by pulling in many extra temporary radials while measuring
FS at a distance without disturbing anything else. If you
see a FS change, you know your system needs work.

One error people make is they measure at too large a
distance. 2 to 5 wavelengths is far enough.

73 Tom