Gentlemen,
Thanks for your interest and comments. Sometimes it improves the received
signal on the other side... sometimes no difference. Most say the QSB fades are
less severe, never eliminated of course. I would say that on average, that the
QSB fading on either linear polarity if about 20-30 dB during liner
polarization, is sometimes improved to 5-15 dB over the short term with
circular. I have noticed that the Japanese flutter over the poles is much less
fluttery in circular polarization, and the other operators have reported the
same... most of the time (when ten was really open two years ago).
Your points:
1. correct, not totally reciprocal, but transmitting circular helps to some
degree most of the time.
2.The ionesphere will randomize the polarization over time, so the arriving
signal is best initially generated circular or eliptical to reduce the worst
case deepest fades over the short term. Long term fading that is caused by lost
propagation path and absorption cannot be helped of course.
3. True. A low gain omidirectional antenna would work almost as well...
generally, but the arriving difference in angle of radiation may cause
additional fading, or enhancement and is less defined as a system. Having the
same gain and the circular wavefront seems to be a more defined system.
Sometimes I see NO difference in circular polarization. Here is something you
may find interesting: Somtimes circular is 3 dB stronger... indicating that the
arriving signal has been faraday shifted to circular and is matching the
"right-hand-sense" of my antenna!!! That was very unexpected and a real eye
opener for me, although that condition is pretty rare. I have aslo noticed that
sometimes the signal is MUCH worse in circular, indicating the arring signal
has been made circular and is OPPOSITE sense and heavily attenuated. I watch
what is going on and play the diversity "game", with some benifit as I attempt
to match the current conditions.
About Your last comment:
More signal was not my goal actually. It was to reduce the severe selective
fading on AM (amplitude modulation) since I spend most of my TEN meter activity
on that mode (29.0-29.1). The distorted AM diring deep selective fades is
anoying sometimes due to the wider bandwidth. My artical started out with this
objective in mind.
In reality, it's fun to chat groundwave on TEN (SSB or AM) with most stations
using the Antron-99 and other verticals for omidirectional QSOs. I live at the
south shore of New york on Long Island, so the gain in either polarity is a
benifit for evening groundwave nets. This was another reason I started with
the dual feedpoint loop, although I planned on the circular (AM/distortion)
experiments. I am having a blast playing with it. To bad ten is slowly dying
out. I may have to add another feedpoint to the 20 meter driven element and try
it there.
George AB2KC
----- Original Message -----
From: Jim Lux
To: GEORGE PRITCHARD ; Richard Karlquist ; RLVZ@aol.com ;
towertalk@contesting.com
Sent: Saturday, November 22, 2003 8:07 PM
Subject: Re: [TowerTalk] Horizontal + Vertical Polarization Question
Interesting writeup, however, I'm not too sure about your statement:
"In as much as a the receiving station benefits from diversity receiving
antennas, the transmitting station reciprocally benefits in providing a more
diverse signal to the receiving station. "
For the following reasons:
1) Ionospheric paths are not reciprocal (Faraday rotation being but one
aspect)
2) On transmit, the goal is to get as much power radiated in the right
direction as possible. Since losses in ground reflections are a significant
effect, and highly polarization sensitive, one is probably best off
transmitting in the polarization that minimizes losses, bearing in mind that
the ionosphere will randomize the polarization on the way to the receiver.
3) On receive, the goal is to get a signal which is above the received noise
floor. For this, CP or a diversity receiver are probably the best bet, since
they minimize the maximum depth of a cross polarization null, and hence improve
the probability that the received signal will be above the noise. For what
it's worth, if what you want to do is merely guarantee that the maximum null
is, say, 10 dB, the diversity antenna can be a lot lower gain (i.e. it can be
an omni) than the primary antenna, and in fact, probably should deliberately be
lower gain (so you don't wind up building an "adding interferometer). This is
only true on HF, by the way, because a higher gain antenna gets more of the
desired signal, but also gets more atmospheric noise. VHF and higher, higher
gain antennas are better, because the noise is in the receiver.
(I maintain that the real value of a gain antenna, on receive, is that it
allows you to remove interference, rather than increase the received signal
power. That interference might be atmospheric noise, which is not uniform
(thunderstorms and the like are localized phenomena))
----- Original Message -----
From: "GEORGE PRITCHARD" <ab2kc@optonline.net>
To: "Richard Karlquist" <richard@karlquist.com>; <RLVZ@aol.com>;
<towertalk@contesting.com>
Sent: Saturday, November 22, 2003 3:59 PM
Subject: Re: [TowerTalk] Horizontal + Vertical Polarization Question
> Gentlemen,
> I am using circular polarization on TEN meters, using a 4 element quad.
> Loops acting as parisitic elements "don't care" about polarity, with NO
> polarization attenuation. That's another reason that quads rule. QSB caused
> by polarity rotations are not isolated by the typical high "vertical to
> horizontal isolation" that the parisitic elements on yagis have. In quads...
> only the driven element attenuates the opposite polarity. For more info on
> the topic of QSB fading with respect to: "Faraday rotations in the
> ionesphere" , please go to the attached link, See my quad (and my son) and
> click on "ARTICAL". http://www.amwindow.org/pix/htm/ab2kc/ab2kc5.htm
> George AB2KC
>
> ----- Original Message -----
> From: "Richard Karlquist" <richard@karlquist.com>
> To: <RLVZ@aol.com>; <towertalk@contesting.com>
> Sent: Thursday, November 20, 2003 10:27 PM
> Subject: RE: [TowerTalk] Horizontal + Vertical Polarization Question
>
>
> > > Has anyone experimented with feeding both a horizontally polarized and
> > > vertically polarized antenna simultaneously on HF? Such as,
> > > feeding a horizontally
> > > polarized yagi and a vertical on 20, 15, or 10 meters?
> >
> > I haven't done that, but I have done a fair amount of A/B'ing
> > of a 20 meter ground mounted vertical vs an inverted vee at 60
> > feet. More often than not, one is better than the other,
> > but it's equally likely to be either one. If you could
> > feed both without destructive interference (and that
> > assumption is by no means assured), then you would get
> > a diversity effect and reduce QSB.
> >
> > I have also A/B'ed 2 verticals 800 feet apart and QSB
> > on them is different (one may be up while the other is
> > down, etc).
> >
> > Hope that helps.
> >
> > Rick N6RK
> > _______________________________________________
> >
> > See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
> Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any
> questions and ask for Sherman, W2FLA.
> >
> > _______________________________________________
> > TowerTalk mailing list
> > TowerTalk@contesting.com
> > http://lists.contesting.com/mailman/listinfo/towertalk
> >
>
>
> _______________________________________________
>
> See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any
questions and ask for Sherman, W2FLA.
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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