"hasan schiers" wrote in message
...
Not vouching for "degree of accuracy", but here's how I estimate
efficiency:

(Known Rrad/Measured R at X=0) at the feedpoint.

If my Inverted L has a predicted Rrad of 25.9 ohms and I measure the
R at
resonance as 29 ohms, the 3.1 ohms is return loss. This would
indicate an
approximate efficiency of 89%.

It seems to me to be a fair approximation. When you have added as
many
radials as possible and watched the input R at the feedpoint (at
resonance)
drop asymptotically toward the predicted or "known" Rrad, your final
"R"
value is used in: Rrad/R. For a perfect ground Rrad = R

I use an MFJ-269 antenna analyzer for the measurements.

Have I gone astray? (aside from my starting value of Rrad, which I
took from
two sources: your rule of thumb formula for Inverted L's, and
ON4UN's Low
Band DX'ing Handbook). Both your formula and ON4UN agree as to the
value of
Rrad for my antenna.

I'll replay to other aspects of your response in another post.

73 and thanks for the new program. As you can tell, I've been
playing with
it. As you can also tell, the implications with respect to length of
radials
required for good efficiency are causing my brain to cramp.

...hasan, N0AN

"Reg Edwards" wrote in message
...

=========================================
Yes Hasan, good agreement. How did you determine
efficiency to THAT degree of accuracy?
=========================================

To Hassan et al,

In all my programs, where antennas are involved, accuracy of results
is usually better than than that needed for the purpose of the
program.

In the case of RADIAL_3 the obvious purpose of the program is to
assist with choosing an economic length and number of radials to be
used with a given test antenna height. It is also educational in that
after reading the introductory notes and using it, the user will have
a better understanding of how radials work.

To summarise, the program tells the user the maximum economic radial
length occurs when the attenuation along it is about 18 to 20dB at the
lowest frequency of use. But where his back yard is not big enough,
even shorter lengths can be quite satisfactory. At HF, where small
standing waves may occur with normal soils, radial lengths can
sometimes be judiciously adjusted to minimise loss.

To increase efficiency when the 20dB limit has been reached it is
necessary to increase the number of radials. And that is subject to
rapidly diminishing returns. As is easily and adequately demonstrated
by the program.

Prediction accuracy can be no better than that of the input data. And
nobody knows what the soil resistivity is in the near field, ie.,
under the antenna, to better than + or - 40 or 50 percent. That's why
NEC4 and the like (or B,L&E) can be no better at predicting results
than RADIAL_3. NEC4 may be highly accurate at predicting radiation
patterns in a hoped-for ideal environment but that is NOT the purpose
of RADIAL_3 which is essentially practical.

If I published the source code hardly anybody would be capable of
making any sense out of it. Some of you old-wives, who imagine you
know more about modelling and programming than I do, would attempt to
ridicule it, thus degrading its usefulness to the ordinary amateur
user. Mud-throwing always sticks.

In the meantime, WW3 is escalating with even greater rapidity!
----
Reg, G4FGQ