Hello all,
I like to share my experiments and hear from your similar experiments regarding
ground conductivity and permittivity measurements.
As we all know (should know), those two parameters are esential to evaluate the
ground under our antennas, especially for verticals.
The ideea to measure the ground concuctivity and permittivity rise after I read
Rudy's (N6LF) article, "Measurement of soil electrical parameter at HF".
I use the "two electrodes" method described on that article which is fine. The
impedance were mesured with a miniVNA.
Not very precise gear but enough for this proposal. The results amaze me...
I start measurements at the end of May. Since then, the weather was very dry
with very few rain shower. Very rough drought this year so, very poor soil
humidity.
In May, conductivity was about 27mS/m and now...only 5mS/m. This is a linear
function because there were no important precipitations.
I have an INV-L (for 160m band) antenna with about 22 optimized radial system
(combined on ground and suspended) with 16m vertical section and about 27m
horizontaly.
The question is:
What is the impact of the conductivity vatiation on the antenna caracteristics?
To answer to this question, I use MMANA-GAL for simulation constructing the
antenna model and using a "real ground" with conductivity as a variable.
First, I use 27mS/m and second, 5mS/m ground conductivity.
Below are the findings.
Conductivity
(mS/m) R(ohm) jX(ohm) SWR(50ohm) Ga(dBi) F/B(dB) Elev.(degree)
27 11.12 -3.354 4.52 3.68
1.19 22.4
5 11.12 -3.354 4.52 3.84 2.26 30.7
I should mention that changing permittivity does not have much impact on this
simulation.
On my view, the important thing to observe on the above data is the Elevation
radiation angle.
It rised with 37% for 81% less conductivity.
Conclusion:
The less ground conductivity the higher is the antenna elevation radiation
angle. This is a negative impact for DX!
There are some observed situations when a higher radiation angle will be better
than a lower one but this is not a rule of thumb.
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Finally, I'd like to hear your comments on this report and also your
experiments.
In the mean time, the measurements of ground conductivity and permittivity are
an ongoing task on my side.
73 de YO3FFF
Cristi
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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