Topband: Modeling "Ground"

[Guy Olinger K2AV]

On Tue, Feb 24, 2015 at 7:36 AM, Richard Fry <rfry at adams.net> wrote:

> NEC4 produces accurate answers for monopole radiators _not_ using
> "overkill" radial systems, as long as the NEC model describes the real
> world conditions for that system.


You wish. You're not considering the situation that everyone is complaining
about.

NEC x.x does not provide accurate answers for "UNDERkill" radial systems
either.

I've never heard of a skilled ham getting trounced on 160 who has a 1/4
wave radiator over an overkill radial system. While it might be argued that
the ham really didn't have to put down that much copper, at worst he only
wasted money. He's still doing right fine getting out on his highly
efficient, if over-coppered antenna, and enjoying it.

On the other hand, UNDERkill radial systems, too short, not enough,
irregular lengths, non-uniform around the compass, especially over poorer
ground, are what NEC x.x also significantly overestimates.

Advice had by many, including myself, has really been off. I still am
waiting for an apology for some glib advice given, resulting in a couple S
units worth of unnecessary loss. I was told some number of times regarding
my complaining of really poor results that I must be doing something wrong,
as the advice had been "verified by professionals and the FCC". I'm still
hearing that selfsame blanket unqualified advice. Wrong then. Wrong now.

Conversions from underkill radials to something efficient designed for
limited space opportunities have generated conversion improvements anywhere
from five to twelve dB, based on before and after strings of RBN reports.
7-8 dB is very common in these conversion exercises, raising suspicions of
some singular issue not treated correctly or at all in NEC. Underkill
radials are proven amplifier neutralizers.

NEC does NOT directly calculate ground losses after the fashion of its
highly accurate wire and tubing calculations. Sommerfeld and all the rest
are tuned APPROXIMATION algorithms that seem well-calibrated only in the
commercial BC paradigm. The NEC ground APPROXIMATION tuning misses by wide
margins in small lots that are not lucky enough to be in 30 mS superdirt.

You can say all you want, but there is now (past tense, already happened) a
massive experience among hams who are using new methods to get a decent
signal on 160, and they just won't believe the old line any more. They have
their own experience in their backyard, and RBN reports, and new signal
reports from longtime ham acquaintances well situated to report general
changes in signal strength. And they simply don't care if NEC is accurate
for commercial grade radial systems. It's a completely useless piece of
information for them.

Most hams do not have the land and circumstances to put down anything
remotely resembling a commercially sized radial system. You're really only
talking to property-rich hams, and leaving the vast majority to learn the
hard way that what you are preaching does not apply to them.

73, Guy.