Re: Off-Topic: Your advice/suggestion about antenna

Posted by Jim Brown-10 on Mar 13, 2020; 9:02pm
URL: http://elecraft.85.s1.nabble.com/Off-Topic-Your-advice-suggestion-about-antenna-tp7658892p7658902.html

On 3/13/2020 12:49 PM, Lyn Norstad wrote:
> I actually do consider 4.7 dbi as "far outperforming" 2.14 dbi (ordinary dipole).

It depends on what you want to achieve. The antenna you describe is a
very old and well accepted design. It's like a beam with a fixed
direction. No question that 2.6 dB can matter under marginal conditions.
I have a 2-el wire 80M Yagi fixed on about 45 deg az that I can reverse
to VK/ZL, which modeling shows gives me about that directivity.

HOWEVER -- in this applications note, I showed that raising a 40M or 20M
dipole by 15 feet will also increase gain at low angles by about 2.6 dB.
See Figs 33 and 41, and the associated text. Doing this uses height to
modify directivity in the vertical plane, without narrowing the
horizontal beamwidth.

http://k9yc.com/AntennaPlanning.pdf

In the same app note, I also showed that mounting an HF vertical on a
roof reduces ground losses and increases gain at lower vertical angles
(below 30-40 degrees) than ground-mounting it. The differences show up
for all soil conditions (except sea water), but are most pronounced for
poor soil.

I showed that the gain of vertical antennas is strongly affected by soil
conductivity, while horizontal antennas are not, but are strongly
affected by mounting height.

And finally, I disproved the myth that antennas must be low for NVIS,
that 75 electrical degrees is optimum, and that raising it to 120
degrees reduces high angle radiation by only 1 dB while increasing low
angle radiation by 6 dB.

Antennas are the component of our stations that are most strongly
dependent on operator goals, real estate, the availability (and the
cost) of suitable skyhooks or towers, their ability to reject local
noise, and restrictions like HOAs, neighbors, and XYLs. No single
antenna is best for all stations or operators. Antennas I can rig here
in my redwood forest would be impossible on the city lot I owned in
Chicago. :)

73, Jim K9YC


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