Reg, a bit confused by these results from RADIAL_3

96 radials, 7MHz, antenna height 10.72m. Soil 500ohm*m,
permittivity
13\

Radials and antenna 1.024mm (18AWG), radials 3mm deep(surface)

Radial Length, %Efficiency

2m, 93.19%
3m, 93.83%
4m, 92.47%
5m, 86.01%
6m, 80.39%
7m, 85.92%
8m, 89.06%
9m, 89.59%
10m, 88.22%
11m, 85.99%
12m, 85.51%
13m, 86.67%

??

Dan
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Dan,

The up-and-down change in efficiency versus radial length is due to
resonance effects. With a high value of soil resistivity of 500
ohm-meters resonance is not completely damped down. This is also
indicated by the relatively small decibels per 1/4-wavelength figure.

As radial length is varied the input resistance of the 96 radials
changes. Look at the wavelength of 1 wire figure. It will be seen
that length passes through 0.5 wavelength resonance at 6.0 metres. It
passes through 1.0 wavelength resonance at 11.6 metres. At both these
lengths the input resistance is at a maximum and so efficiency is at a
minimum.

At 2.9 metres and 8.8 metres the radials are in 1/4-wave and 3/4-wave
resonant and the input resistance is at a minimum and
efficiency is at a maximum.

Vary length while watching the resistive component of input impedance
to see what happens. It's highlighted in red.

If you reduce soil resistivity from 500 to 50 ohm metres the resonance
effects will probably disappear and the decibels per quarter
wavelength will increase. All resonant effects will have disappeared
when radial attenuation is about 18 or 20dB or greater.

The effects of resonance are not observed so well when frequency is
varied because so many other things change as frequency is varied over
an octave or more.

Resonant effects are much greater at 20 MHz and above with very high
resistance soils such as desert sand. The radials then behave very
similarly to the elevated variety.

I trust your confusion has now gone away. ;o)
----
Reg, G4FGQ