"Reg Edwards" wrote in message
...

"Frank's" wrote
Reg, with the antenna we have established as our test model:
All wires #14, monopole 9 m, 36 X 10m radials 25 mm below
ground. Ground parameters Er = 16, resistivity 150 ohm-m.
I have calculated the radiation efficiency including the surface
wave. What is interesting is that the surface wave contributes
very little at elevation angles over 10 degrees.

For 100 W input the total radiated power, not considering
the surface wave, is 31 W. When the surface wave is
included the total radiated power is 36 W.

==========================================
Frank,

So the missing 64 watts, if not dissipated in the radials must be
dissipated in the soil under the antenna.

To prove something, what is the efficiency when the ground is sea
water. Resistivity = 0.22 ohm-metres and permittivity = 80.

PLEASE CONFIRM THE NUMBER OF RADIALS.

I thought you were unable to model 36 radials. Were you using only 1
radial? With only 1 radial my program makes efficiency = 28 percent.
Which would be satisfactory agreement with your 36 % )

Or did you substitute the radial system with a lumped resistance of 5
ohms which I suggested could be used when estimating efficiency?


Reg,

The antenna has thirty-six 10 m radials, 25 mm below ground. The input
impedance at 8.07 MHz is 36.3 - j 2.0. I used 0.2 ohm-m for sea water
resistivity as it seems to the accepted standard. The radiation efficiency,
not including the surface wave, is 93.6 %. I can add the surface wave
if you are interested, but it is a little tedious to convert the far field
surface wave, in cylindrical coordinates, to normalized spherical
coordinates; which is the form NEC produces for the sky-wave
components.

Frank