On 17 Aug 2004 11:12:46 GMT, oUsama (Yuri Blanarovich)
wrote:

I thought that antenna is supposed to radiate RF in the direction and with
pattern one desires. That's what I want to measure, how effective radiator it
is, how much RF it produces at the point of interest.

Of course that is what everyone would want to measure, but unless you
are working in the millimeter bands in a non-echoic chamber,
determining the true (absolute) radiation pattern can be quite
problematic.

You could fly around in a plane with a calibrated field strength meter
in trying to determine the true radiation pattern of the antenna.
However, the variations in ground conductivity may create a large
variations if the measurement is repeated at different places,
especially with unbalanced antennas.

Thus, it would help a lot, if the efficiency could be determined
separately from the radiation pattern, since much of the calibration
problems could be eliminated. The calorimetric method of measuring the
heat dissipated by the losses is one usable method to get the
efficiency.

If some manufacturer claims extraordinary _gain_ figures for some
LF/MF/HF antenna, you should publicly ask which plane was used for the
measurement and when were these measurements made. You can then check
the local airports, if that plain was in the air at that time.

Paul OH3LWR