Re: Length & number of radials


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

.

Relevant Pages

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