<< Of course the real world FS is ALWAYS much less than the theoretical
maximum over perfect soil at one km, so the mV/m/km value you read
about is never a "real" measured value. >>
I would like to add a little buit of additional information to what Tom wrote.
I have done a lot of these types of measurements and analysis since that is
what I do for a living .
You can see as much as 10-15% lower fields (from the theoretical predicted
values) after analysis of the measured data. It is also a good idea to
measure the complete pattern of the antenna after making any changes. Yes,
it is a lot of work, but just doing the measurements in one direction (radial)
does not give you much qualitative data to make a good evaluation of the
performance. In the broadcast industry we normally measure at least the eight
cardinal bearings (0, 45, 90, 135, 180, 225, 270, 315 degrees) out to about 20
miles (32 km) to "prove" the radiation pattern of the antenna. The same rule
of thumb would be good to follow when determining the measured radiation
efficiency of a 160 antenna. By going out to 20 miles, you can obtain enough
data to wash out any measurement anomalties that might show up.
As Tom says, read part 73 of the FCC Rules. This describes the entire
procedure in detail.
73................de Goose W8AV
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