Topband: Radials, EZNEC and far field

[Frank W3LPL]

Hi Ignacy -

There's little hope that a vertical antenna hundreds of miles
from salt water can ever close the gap with an antenna built over
a salt marsh or within about a wavelength of salt water.

The purpose of radials is reduce losses in the power transfer
between a feedline and a vertical antenna. Their effectiveness is
best measured by measuring the RF current at the base of the vertical.
Highly effective radial systems produce significantly more RF current
in the vertical than a sparse radial system.

Radials cover a very small fraction of the very large reflection zone
(Fresnel zone) that produces low angle radiation.  A vertical over a
salt marsh or within about a wavelength of salt water will produce
6 dB or more of gain at low angles compared to a vertical with poorly
conducting soil in its reflection zone. 

Radials have no useful effect in improving low angle radiation,
low angle radiation from vertical antennas is determined almost
entirely by highly conductive soil or salt water in the large
reflection zone.

73
Frank
W3LPL




----- Original Message -----
From: "Ignacy Misztal" <no9e at arrl.net>
To: "topband" <topband at contesting.com>
Sent: Monday, December 19, 2022 10:50:53 PM
Subject: Topband: Radials, EZNEC and far field

Do more radials on a 160m vertical bring more improvements than shown
by simulation?

Most simulations, e.g. by EZNEC, show that going above 32 radials on 160m
brings  minimal improvement, say 1 db to 2 max. Even for low angle signals.

On the other hand, some really loud stations on 160m, that are 5-10 db above
 the crowd, use a massive amount of radials. This is for inland  stations,
far away from salt water.

Is there any discrepancy between modeling by EZNEC and real life
performance with the number of radials? Does adding radials beyond 32 help
much for low angles?

Any real story?

I have a shunt-fed 100 ft tower with 36 100ft radials. It is vastly
inferior to a 40 ft high  inv L with 1 radial by salt water that hears DX
loud 2 hrs before the sunset. I am wondering whether by  expanding to 50
200ft radials would narrow the difference.

 Ignacy NO9E
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