Jim
That is basically N6LF's and my approach so far as well.
As I said I was hoping for a more direct measurement approach that
didn't involve an actual antenna.
I basically live on a large (prehistoric) sandbar approximately 65 feet
above MSL. ( A mountain ridge by Florida standards) A tidal river is
~1/4 mile away
Dave
NR1DX
On 2/13/2021 3:22 PM, Lux, Jim wrote:
On 2/13/21 10:57 AM, Richard (Rick) Karlquist wrote:
Just a heads up:
Gerry Burke, of LLL/NEC fame had some discouraging news
about their ground measurements.� He told me that in
some cases there was no configuration of NEC parameters that would
correlate with some real life ground measurements.
Alan Christman's PhD dissertation talks about this too:
https://etd.ohiolink.edu/apexprod/rws_etd/send_file/send?accession=ohiou1172605318&disposition=inline
Burke, G. J., "Recent advances to NEC: Applications and Validation",
UCRL-100651, 3 March 1989
The other disclaimer is that NEC only models a uniform ground.
I know my ground is far from that.� After 1 to 5 feet of pure
clay, I hit "cemented hardpan" waterproof clay.� About 40 feet
down I hit sand, according to the well diggers.� No way to
model that with NEC.
This is very much so. What I do is model with NEC and use several
different ground properties, varying both sigma and epsilonr, and see
how much difference it makes.
I did some analysis for the� OVRO - Long Wavelength Array, which is a
field of hundreds of fan dipoles.� They had some buried probes that
measured actual RF properties, and data for about half a year (long
enough to see rain storms, snowmelt, etc.).� What we were interested
in is whether the "ground screen" under the dipoles made a big or
little difference.
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