From: n4is@comcast.net
To: jkaufmann@alum.mit.edu; topband@contesting.com
Date: Wed, 17 Dec 2014 23:11:10 -0500
Subject: Re: Topband: 8 circle: DXE vs Hi-Z
Hi guys
Polarization does play a lot on 160m for two reasons. I can say that
because
I am using my HWF (two horizontal flags end fire) since 2009. The first
one
is local man made noise that propagate only vertical due the attenuation
on
the horizontal component near the ground. And Second the DX signal always
come in both polarization.
The result form the two reasons is an optimized signal to noise ration
using
horizontal polarization.
I have both WF with the same RDF, during SR or SS there is almost no sky
noise coming from the back because of the darkness, however local man made
noise comes from any direction, especially if you live in a city lot like
I
do. Most of the time the noise is coming at the same direction you want to
hear the DX, and if you add power line noise the situation deteriorates a
lot for the VWF due vertical polarization. Using my HWF I normally get 10
dB
better SNR than my VWF that has the same RDF and same aperture of 74
degree
measures, I can turn the antenna and measure it, they are not optimized
for
best F/B, I optimized them for maximum rejection of local man made noise.
The HWF is not a dipole. The two phased loops take of angle us 40 degree
and
there is a huge attenuation for signals above 60 degree. Low dipole is a
huge issue if the dipole is resonant, it will interact with all other
receiver antennas and will destroy directivity of all of them, if you want
to use a low dipole make it not resonant. Gain in not important so it can
be short as a 30 m dipole and still will hear the same way. Another issue
with low dipoles is the amount of energy absorbed from the TX antenna. If
you connect a power meter and a 50 ohms load o the low dipole and transmit
KW on the TX antenna, you can measure several WATTS at the low dipole .
You
can burn you front end with a low resonant dipole.
Adding to all that there is another very interesting observation from my
last 5 year using a high RDF horizontal RX antenna, when the TX signal
refract on the ionosphere the signal split in two waves, that was very
well
explained by K9LA. What I observed is that these two waves does propagate
in
different directions. I normally receive VK6 near my SR with better SNR
horizontal from 210 degree SSW and with better SNR from 280 degree
vertical.
Sometimes the horizontal peak is 20 minutes before the vertical peak that
is
most of the time at my SR.
73's
N4IS
JC
-----Original Message-----
From: Topband [mailto:topband-bounces@contesting.com] On Behalf Of John
Kaufmann
Sent: Wednesday, December 17, 2014 8:59 PM
To: topband@contesting.com
Subject: Re: Topband: 8 circle: DXE vs Hi-Z
Good points about polarization. If the signals and/or noise are polarized
predominantly in one state, then RDF may not be a good predictor of SNR
performance, particularly if the antenna receives predominantly in an
orthogonal polarization. On the other hand, if the polarization state of
the signals and noise evolve randomly with no preference for any one
state,
which is often assumed for skywave signals, then RDF will be--on
average--a
good receiving metric, subject to the previous stated qualifications about
the spatial distribution of the received noise. However, some of the past
discussions on this reflector about preferential polarization of skywave
signals on 160 may call into question the assumption of randomly polarized
signals.
73, John W1FV
-----Original Message-----
From: Topband [mailto:topband-bounces@contesting.com] On Behalf Of Richard
(Rick) Karlquist
Sent: Wednesday, December 17, 2014 3:19 PM
To: Lee K7TJR; 'Terry Posey'; 'John Kaufmann'; topband@contesting.com
Subject: Re: Topband: 8 circle: DXE vs Hi-Z
All this discussion about RDF overlooks the issue of polarization. If you
make an array of verticals with a certain RDF (assuming noise comes from
all
directions uniformly), the array will be better than an individual
vertical
by the RDF factor. However, what I have found is that a horizontally
polarized antenna, such as a low dipole frequently receives considerably
better than a vertical. In that case, you would be better off using an
array of low dipoles. The reason why horizontal polarization can be
better
is that the horizontal component of terrestrial based noise is highly
attenuated over distance as a ground wave.
Rick N6RK
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