Hi Tom,

I understand there are measurement issues (and certainly assumption issues
for Rrad). Isn't is fairly certain that increasing the number of radials (of
proper length) until the feedpoint R (at resonance, at the antenna) no
longer drops, is a reasonable approximation of "high efficiency"? The only
issue I see, is determining the target Rrad to compare it to when trying to
"estimate" efficiency.

Are you saying (for example), that the feedpoint R of a 1/4 w vertical
against perfect ground cannot be reliably estimated at 37 ohms? If it can,
then isn't 37/R a measure of efficiency?

Again, I'm thinking of the efficiency of the ground system... I have no way
to look at field strength.

Is it really possible to reduce ground losses to the absolute minimum and
not have a corresponding increase in field strength?

This is starting to turn into "black magic" for me. I can understand
questioning a particular "number" for efficiency based on the simplistic
Rrad/R formula. If the implications go further...indicating there is no
meaning to Rrad/R, then I'm lost.

Perhaps the issue is that it's known how to maximize efficiency, it's just
completely unknown what that efficiency really is, and there is no simple
way to measure it. If that's what your saying, then I understand.

That position does seem to muddy up the "how many radials and of what
length" efficiency info presented in ON4UN's book and referenced in other
texts. They all seem to acccept some sort of accuracy for the Rrad/R formula
with 1/4 w verticals. If I understand you correctly, the formula is rejected
outright as hopelessly simplistic, and of no particular value.

Do I have it now? If so, I'll refrain from using it in the future.

Thanks for the comments.
73,

....hasan, N0AN


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hasan schiers wrote:
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%.

Hi Hasan,

Roy Lewallen and I just measured some ground systems. Actual
measurements using good instruments, not guesses or models.

In one case we had an antenna with four elevated radials that within
measurement error (using lab type gear) had equal signal strength level
as the very same vertical element over 16 buried radials. As I recall
the buried radials had over 60 ohms of base impedance, the six foot
high elevated radials was down around 40 ohms or less.

Over the years I have measured many antenna with very low base
impedance and terrible efficiency, I have measured verticals where
changing the ground system did not change impedance but improved field
strength, and it is very easy to find cases where changes in a ground
system can have MORE efficiency with higher feed impedance without
changing anything but the ground system.

Over simplification of a complex system will often not produce reliable
results. Just look at the results of Reg's progam where it predicts
highest efficiency with very short radials. We all know that doesn't
happen, but the oversimplified program says it does.

73 Tom