Exactly! How can you know what your ground is REALLY like, especially when
you go underground? (and even if you knew, how could you model it?)
I'm really not interested in trying to get an accurate model. It's just
that I have ALWAYS used a horizontal Dipole at just 50ft for working DX on
Top Band. Yet I've always done pretty well - most people on here tell me my
signal is comparable with most of the other EU signals, who all use decent
verticals.
Now I'm pretty sure that most 160m DX propagation ISN'T as low angle as most
people think (like it usually is on 80m) . . . but equally I believe that my
Dipoles simply CAN'T be the "cloud warmers" that the theoretical plots from
EZNEC etc predict!
About 20 Years ago I actually did a load tests on SSB with a good friend of
mine who had a full sized vertical and 50 radials (this was over a period of
months) . . . we made sure we were running the same power, and each night we
did this, we got critical comparison reports from dozens of stations right
across North America . . over 80% said we were the same strength!
Roger G3YRO
-----Original Message-----
From: Richard (Rick) Karlquist [mailto:richard@karlquist.com]
Sent: 08 November 2018 00:00
To: Roger Kennedy; topband@contesting.com
Subject: Re: Topband: Accuracy of modeling of 160m verticals
If you really want to get accurate ground modeling, you need to follow
N6LF's procedure. He installs low dipoles at various heights over his
ground and measures their impedance and resonant frequency.
He then models them on NEC4 and tweaks the ground parameters to get the
model to agree with the measured data. This is repeated on each band of
interest.
The other problem is that the ground may not be homogeneous, in either the
horizontal direction or the vertical direction. Not to mention seasonal
moisture effects.
If you can manage a low dipole, there is a good chance you reconfigure it as
a T-top loaded vertical with a few elevated radials. That is likely lead to
a worthwhile improvement in performance over any kind of ground.
73
Rick N6RK
On 11/7/2018 3:19 PM, Roger Kennedy wrote:
>
> Actually, I'm rather sceptical about the accuracy of theoretical
> antenna modelling software generally on 160m. (as per my recent
> discussion on a well-known Forum)
>
> I'm not convinced that the various programs (which all seem to give
> different projections) properly take into account the different kind
> of REAL ground under the antenna . . . particularly with a low Dipole
> like I use - which is equivalent to a 20m Dipole just 3ft off the
> ground ! (and therefore the ground has a HUGE effect on the antenna)
>
> Roger G3YRO
>
> _________________
> Searchable Archives: http://www.contesting.com/_topband - Topband
> Reflector
>
>
_________________
Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
|