Topband: Accuracy of modeling of 160m verticals

[JC]

Hi Roger

I used a dipole for several years too. Actually took me 20 years to work my
first DXCC on 160m from SPaulo Brazil using them..

Here is the thing, your horizontal dipole is not 100% horizontal polarized.
It is only 50% horizontal and 50% vertical.  You can see it on EZENEC
selecting 3 D and NO TOTAL FIELD, just red for vertical and green for
horizontal field.

Even a perfect straight line dipole, without the feed line, is 50 % vertical
and 50% horizontal, Vertical along the wire like a Beverage antenna, and
broadside horizontal. If the ends are close to the ground like an inverted V
the, the vertical polarization take off angle will be lower than the
horizontal one.

However you have a feed line and without an excellent BALUN, very hard to
find one for 160m, your feed line is a vertical antenna by itself, and the
vertical polarized wave on your dipole will have a lower take off angle is
all directions.

Any vertical antenna is 100 % vertical, but all horizontal antennas close to
the ground are not 100% horizontal. 

On 160m all antennas are very close to the ground.

If you have a tower or any other vertical structure near your dipole, guess
what , it will be feed by the dipole and irradiate vertical as well.

Always use both polarization on EZNEC to understand what the antenna is
doing.

73's
JC
N4IS








-----Original Message-----
From: Topband [mailto:topband-bounces at contesting.com] On Behalf Of Roger
Kennedy
Sent: Thursday, November 08, 2018 4:51 AM
To: topband at contesting.com
Subject: Topband: Accuracy of modeling of 160m verticals

 
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 at karlquist.com]
Sent: 08 November 2018 00:00
To: Roger Kennedy; topband at 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
> 
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