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

Posted by Lyn WØLEN on Mar 13, 2020; 10:05pm
URL: http://elecraft.85.s1.nabble.com/Off-Topic-Your-advice-suggestion-about-antenna-tp7658892p7658903.html

Jim -

Your antenna research is impressive.  I have downloaded the PDF and will
spend some time studying it.  Thanks.

One question I have relates to NVIS.  In the case of my 80 meter EDZ, the
plan was to make it workable for NVIS operation.  It has succeeded in that
regard very nicely in that I can cover the entire state of Illinois (which
is primarily a N-S pattern) very well on both 80 and 160.  We operate a
state wide ARES/RACES net on 80m, but there has been some fear that as
propagation continues to worsen for a period, the MUF for NVIS will require
a higher frequency than non-NVIS and one that actually approaches the MOF at
that time - due to the angle of radiation.  In other words, using an NVIS
antenna when the MUF is 4.0 MHz might actually require an MUF of 12 - 13 MHz
which would be closer to the MOF at that same point in time.

Have you observed that at any extremely low spot in the cycle?

We have seemingly remedied that by setting up and operating a successful
160m net and passing digital traffic.

73
Lyn, W0LEN  

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Jim Brown
Sent: Friday, March 13, 2020 4:03 PM
To: [hidden email]
Subject: Re: [Elecraft] Off-Topic: Your advice/suggestion about antenna

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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