"Richard Clark" wrote
"Richard Fry" wrote:
Nowhere in Brown, Lewis and Epstein's IRE paper titled "Ground Systems as
a
Factor in Antenna Efficiency" is there ANY documentation of the actual
ground conductivity that was measured, or even calculated for the antenna
site and/or the propagation path used. It was unimportant for the
construct
and relevancy of the tests and conclusions which the paper reported.

Hi OM,
Both Reg and you would do well to obtain and read a copy....
the discussion of earth conductivity (quite specifically named as
such) within the paper spans pages 757, 758, 759, 760, with numerous
citations and graphings against specific conductivity values applied
to related figures in page 761, 762, 763, and 764. ... (etc)

I have the paper, and have read it carefully, many times. The paper gives
equations and graphs for current in the radial wires for a perfectly
conducting Earth, and for Earth conductivities of 20 x 10^-15 e.m.u. and 100
x 10^-15 e.m.u. Later, in the experimental data, they report measurements
of the currents for various radial configurations during their measurement
sequences. But as I wrote, nowhere do they specifically report the actual
ground conductivity for the antenna site, or along the 0.3 mile propagation
path of the test. If you can find that anywhere in that paper, I will
promptly retract my statement, and apologize.

Figure 30 in the paper shows that the ground system comprised of 113 radials
of 0.412 lambda each resulted in a measured field strength that was about
0.18 dB below the theoretical value for it from a 90 degree radiator against
a zero-ohm connection to a perfect Earth. I expect most of us would be
quite happy if our measured data agreed that closely with its theoretical
value. In any case it does show that the actual value of the ground
conductivities for the test site and path had a trivial bearing on the test
results, e.g., it was unimportant.

In fact the efficiency of AM broadcast vertical radiators per the FCC
definition always is based on a perfect ground plane, and two ohms or less
of DC resistance in the transmitter connection to it (via the radial ground
system). Only then is distant field strength determined, using the radiator
efficiency value and applied RF power along with the appropriate FCC
propagation curve for the frequency and Earth conductivity for the path.

RF