Topband: Vertical antennas aren't always best for DX
John Kaufmann
john.kaufmann at verizon.net
Tue Nov 27 09:35:52 EST 2018
JC,
You said: " Every dipole or inverted V irradiate 50% of the power
horizontal polarized broadside with the wire and 50% of the power vertical
polarized along the wire." You cited EZNEC as evidence.
I am merely pointing out that as a general rule, this is not true. The
issue *is* math because that is precisely how you determine the fraction of
power that goes into horizontal polarization and into vertical polarization.
As I pointed out, the relevant math is a 3-dimensional integration of the
radiation pattern in spherical coordinates.
Take a dipole that is 1/4 wavelength high, which we can all agree is "low"
in wavelength terms. At a takeoff angle of 90 degrees (straight up), EZNEC
shows that the horizontal and vertical components of radiation are about the
same. It is easy to think there is a 50/50 split in horizontal/vertical
power because of this. However, this neglects the radiation at lower angles
where the large majority of the radiated power is produced. At a 45 degree
takeoff angle, the broadside horizontal power dominates the vertical power
by about 4 dB and the ratio increases at lower angles. If the dipole is
higher than 1/4 wavelength, the ratio becomes even greater.
The math does not lie.
73, John W1FV
-----Original Message-----
From: Topband [mailto:topband-bounces at contesting.com] On Behalf Of
n4is at n4is.com
Sent: Tuesday, November 27, 2018 8:50 AM
To: jkaufmann at alum.mit.edu; topband at contesting.com
Subject: Re: Topband: Vertical antennas aren't always best for DX
John
The issue here is not math. It is the interaction of fields and matter. A
good text book is Electromagnetic waves and radiating system by Edward C
Jordan and Keith G. Balmain. Chapter 9.
You can not ignore the close proximity with ground on 160m antennas for both
transmit signal and receiving signal. Too close it became more a
transmission line, getting high the irradiation increase and the maximum
horizontal power radiated or receiving signal intensity are near 1 ½ wave
high. The take off angle depends on the ground itself.
73’s
JC
N4IS
From: John Kaufmann <john.kaufmann at verizon.net>
Sent: Tuesday, November 27, 2018 8:16 AM
To: n4is at n4is.com; topband at contesting.com
Subject: RE: Topband: Vertical antennas aren't always best for DX
In considering the *total power* radiated by any antenna, you need to look
at the 3-dimensional antenna pattern, not a 2-dimensional slice. The total
radiated power is the 3-dimensional integration of the 3-dimensional
radiation pattern. It is convenient to do this in spherical coordinates
because that is how we visualize 3-dimensional patterns. In spherical
coordinates the integration applies the *smallest* weighting at elevation
angles around zenith. Even if the dipole is low, the calculation shows that
the fraction of power that goes straight up is small compared to the total
radiated power. This is easily understood in 3-dimensional spherical
coordinates:
https://www.khanacademy.org/math/multivariable-calculus/integrating-multivar
iable-functions/triple-integrals-a/a/triple-integrals-in-spherical-coordinat
es.
73, John W1FV
-----Original Message-----
From: Topband [mailto:topband-bounces at contesting.com] On Behalf Of
n4is at n4is.com <mailto:n4is at n4is.com>
Sent: Tuesday, November 27, 2018 6:58 AM
To: jkaufmann at alum.mit.edu <mailto:jkaufmann at alum.mit.edu> ;
topband at contesting.com <mailto:topband at contesting.com>
Subject: Re: Topband: Vertical antennas aren't always best for DX
Sorry , but all antenna's on 160m are close to the ground and it is the
case, you can check by yourself using EZENEC if you don't know how to
calculate the fields.
There is no misleading here.
73
JC
N4IS
-----Original Message-----
From: Topband <topband-bounces at contesting.com
<mailto:topband-bounces at contesting.com> > On Behalf Of John Kaufmann
Sent: Monday, November 26, 2018 8:53 PM
To: topband at contesting.com <mailto:topband at contesting.com>
Subject: Re: Topband: Vertical antennas aren't always best for DX
The statement that the half of a horizontal dipole's radiation is vertically
polarized is misleading and needs qualification. There is a vertically
polarized component off the ends of the dipole but it is only of consequence
at takeoff angles approaching 90 degrees, in other words straight overhead.
I would argue that these takeoff angles are of little interest for long
distance propagation.
At takeoff angles lower than 60 degrees or so, the total radiation pattern
of a dipole at any reasonable height becomes dominated by the horizontally
polarized component that is broadside to the dipole. The lower the angle
or the higher the dipole, the more insignificant the vertical component
becomes. This is all verifiable in EZNEC. If this were not true, you would
not see the well-defined radiation patterns that are produced by HF Yagi's
at higher frequencies were the radiation is horizontally polarized for
virtually all signals of interest.
73, John W1FV
-----Original Message-----
From: Topband [mailto:topband-bounces at contesting.com] On Behalf Of
n4is at n4is.com <mailto:n4is at n4is.com>
Sent: Monday, November 26, 2018 11:06 AM
To: 'Roger Kennedy'; topband at contesting.com <mailto:topband at contesting.com>
Subject: Re: Topband: Vertical antennas aren't always best for DX
Roger
Every dipole or inverted V irradiate 50% of the power horizontal polarized
broadside with the wire and 50% of the power vertical polarized along the
wire. After the first refraction it does not matter.
This is an electro-magnetic wave law. You can check that on EZENEC, it is
not a anecdote.
The advantage over vertical 1/4 wave antenna is efficiency. The vertical
efficiency depends on the ground plane resistance, it is common to see
invert L with only 50 % irradiated power, the other 50% is dissipated on the
ground.
"In Theory, we know everything, but nothing works"
"In Practice, everything works, but we don't know why"
We never will fully understand the 160m band.
73's
JC
N4IS
_________________
Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
_________________
Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
_________________
Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
_________________
Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
More information about the Topband
mailing list