FWIW: When we moved here in 2015, I joined the W7RN crew and began to
use the station remotely. Very high Coefficient of Aerial Aluminum on 7
or so towers, very low noise levels. I had been checking into the
NorCal traffic net on 80 and wanted to continue. The main 80 meter
antenna at W7RN is a near-full-size 3-el yagi at about 160 ft [~48 m].
It fires flames at Mongolia very nicely, however the NorCal stations at
80-150 mi [130-240 km] from me were around S5-S7.
Here at home, we are members of an HOA, everyone can fill in the blanks
from that. Just for grins, I installed an end-fed wire I got on-line on
the wood fence. It runs on electric fence insulators and is about 6 ft
[1.8 m] high, with a 90 deg bend about 1/3 of the way down. CA stations
on 80 are 10 to 20 dB over S9 on it. I have discovered that it actually
works way better than I expected for NA contacts, and hits KH6 pretty
well on 20. I make a lot of Q's with it in the Wednesday CWOps Tests
when I manage to get on. I won't make Honor Roll with it, but it is
very surprising at 100 W from my K3. I bought another and will use it
into a tree from Pershing County NV in the 7QP next weekend.
Our fan dipoles in SE Asia were 20-30 ft high at most and worked just
fine, even to the Philippines. For emergency uses, I'd worry less about
the mathematics of antenna radiation and attempting to precisely
optimize it, and much more about ease of installation and survivability.
If it isn't buried and you can cram power into it [and Elecraft ATU's
are very good at that], it will radiate.
73,
Fred ("Skip") K6DGW
Sparks NV USA
Washoe County DM09dn
On 4/30/2017 3:49 PM, Ron D'Eau Claire wrote:
Ground losses mount rapidly as a horizontal antenna is lowered closer to the
earth. So, while the pattern may show the main lobe straight up, the amount
of RF lost in the earth below increases.
EZNEC confirmed to me that about 0.2 wavelengths up is the optimum height
for the strongest vertical lobe (NVIS pattern). That fits with the fact that
0.2 wavelength spacing between the driven element and reflector of a Yagi
produces the maximum gain. Running a wire near the ground helps too, since
the earth is, at best, a poor dielectric instead of an efficient reflector.
Well supported towers have withstood some serious quakes, including our
land-mobile repeater towers in the Loma Prieta earthquake that broke the
S.F. Bay bridge and knocked down a good part of downtown Santa Cruz back in
the 80's.
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