The majority of antennas used today are (commercial) circularly
polarized
Ham antennas remain in the linear domain (ala the Yagi and similar)
There are many reasons espoused in CP advantages in "point to point"
What is the main advantage hams hold over the more popular circular
polarized antennas in its "skip" type useage versus "point to point" ?

On Sun, 9 Aug 2009 21:24:01 -0700 (PDT), Art Unwin
wrote:

The majority of antennas used today are (commercial) circularly
polarized
Ham antennas remain in the linear domain (ala the Yagi and similar)
There are many reasons espoused in CP advantages in "point to point"
What is the main advantage hams hold over the more popular circular
polarized antennas in its "skip" type useage versus "point to point" ?

Huh? By "skip", I presume you mean for HF and DX. Numbers are always
nice.

There are CP antennas for HF:
http://www.bruhns.us/CP_on_HF/CP_on_HF.html
www.roke.co.uk/resources/datasheets/locate-sarsen.pdf
www.ascsignal.com/images/content/gov_radar/pdfs/TA103.pdf
http://www.antennaproducts.com/ht30detail.html
The main advantage is that they deal with multipath better and don't
have a deep cross polarization null. I've never tried one so I have
no idea how well (or badly) they work.

For what it's worth, we did some experimentation with CP on 146MHz
repeaters in the 1970's. The results were an impressive reduction in
"picket fence" type of fading for mobiles. However, the anenna gain
was less than an equivalent size linear array, so there was some range
reduction.

Mo
http://www.qsl.net/n/n9zia//cir_pol_rpt.html

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Jeff/Art

Keep in mind too that cross polarized (circular) point to point links
(ie with a CP ant at each end) suffer from odd reflection attenuation
(ie the polarization sense gets reversed by reflection)

In 70cm UHF experiments I did back in the 80's I found out that a
horiz-horiz system (base to mobile) outperformed a circular-circular by
at least 12dB when moving. This wasnt actually the base reason for the
experiments so I didnt make accurate measurements.

OT Art, but I hope interesting.

How random is the propogated linear antenna HF wave polarization and
does it vary much with single hop and/or high angle? That might be a
starting point for determining how useful CP on HF might be.

Tnxs for the link Jeff.

Cheers Bob VK2YQA

Jeff Liebermann wrote:
On Sun, 9 Aug 2009 21:24:01 -0700 (PDT), Art Unwin
wrote:

The majority of antennas used today are (commercial) circularly
polarized

On Aug 10, 6:29*am, Bob Bob wrote:
Jeff/Art

Keep in mind too that cross polarized (circular) point to point links
(ie with a CP ant at each end) suffer from odd reflection attenuation
(ie the polarization sense gets reversed by reflection)

In 70cm UHF experiments I did back in the 80's I found out that a
horiz-horiz system (base to mobile) outperformed a circular-circular by
at least 12dB when moving. This wasnt actually the base reason for the
experiments so I didnt make accurate measurements.

OT Art, but I hope interesting.

How random is the propogated linear antenna HF wave polarization and
does it vary much with single hop and/or high angle? That might be a
starting point for determining how useful CP on HF might be.

Tnxs for the link Jeff.

Cheers Bob VK2YQA

Jeff Liebermann wrote:
On Sun, 9 Aug 2009 21:24:01 -0700 (PDT), Art Unwin
wrote:

The majority of antennas used today are (commercial) circularly
polarized

What stands out for me is the audio improvement.

On Aug 10, 8:23*am, Art Unwin wrote:


What stands out for me is the audio improvement.

Only very high Q antennas should noticeably effect audio.
Comparing a dipole to say a turnstile, you should notice
no real difference at all.
I've used turnstiles on 75 and 40 meters for years.
They work very well, but audio improvement is not
one of the usual features noted.
I prefer a turnstile over a dipole on the low bands
if I have my choice.
They seem slightly more efficient overall, but I've
never done any accurate testing. They also tend
to fill in the nulls off the ends that a dipole can show.
I've heard that running a circular polarized antenna
like the turnstile on HF, only shows circular polarization
at the higher angles. Which is what I'm usually using
when working NVIS on the lower bands.

wrote in message
...
On Aug 10, 8:23 am, Art Unwin wrote:


What stands out for me is the audio improvement.

Only very high Q antennas should noticeably effect audio.
Comparing a dipole to say a turnstile, you should notice
no real difference at all.

I have though that also, but I have noticed that on 75 meters there
sometimes seems to be a differance in the voice of the other station when I
switch from my off center fed antenna at 50 feet and a dipole at 20 feet.
This is when signals are around the same on either antanna. Around the s-9
point. I am using an Icom 746pro and an external switch to change the
antennas.

On Mon, 10 Aug 2009 06:29:03 -0500, Bob Bob
wrote:

Keep in mind too that cross polarized (circular) point to point links
(ie with a CP ant at each end) suffer from odd reflection attenuation
(ie the polarization sense gets reversed by reflection)

That's one of the big advantages of CP for point to point links. The
polarization reversal on odd numbered reflections means that multipath
is greatly reduced.

In 70cm UHF experiments I did back in the 80's I found out that a
horiz-horiz system (base to mobile) outperformed a circular-circular by
at least 12dB when moving. This wasnt actually the base reason for the
experiments so I didnt make accurate measurements.

The book "Microwave Mobile Communications" by Willaim C. Jakes Jr
(1974) has a few words on the subject. As I recall, Ma Bell concluded
that neither linear or cirucular polarization is good enough and that
some form of diversity is required.

Incidentally, "The Practical Handbook of Amateur Radio FM and
Repeaters" (1981) (Tab 1212) by Pasternak and Morris, has chapter 31
on CP tests on the WA6VQP repeater on Loop Mtn. They draw a polar
plot of the measured repeater antenna pattern and note that they get
the typical "flower" pattern, with attendent deep nulls with linear
polarization. With CP, the nulls are far less pronounced.

My tinkering in the 1970's was specifically to reduce severe multipath
fades along a section of freeway in Smog Angeles. It worked, but with
some loss in signal stength from mismatched linear and CP
(theoretically -3dB).

OT Art, but I hope interesting.

How random is the propogated linear antenna HF wave polarization and
does it vary much with single hop and/or high angle? That might be a
starting point for determining how useful CP on HF might be.

I did some tinkering with measuring the polarization of skywave
signals using a rotating loop antenna. Including Faraday rotation, my
guess(tm) is that it's quite random and changes rapidly.



--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

I also did some experiments in the early '70s to see if CP would reduce
fading. I built a couple of types of omnidirectional CP antennas -- a
"skew planar", and a copy of a commercial FM BC antenna, for mobile use
with the local 450 MHz repeater. I soon discovered that as soon as I
placed the antenna over the top of the car, the polarization became
nearly linear. I've since learned that it's because of the nature of the
reflections from the ground plane, and it's easily seen with EZNEC+.
When I put the antenna far enough away from the car to minimize
reflections, the lowered gain offset any possible advantage. Overall,
they worked out worse than a conventional vertically polarized antenna.
It might have been interesting to try CP at the repeater, but that was
never done.

The problem with ground reflection ruining the circularity makes it very
difficult to achieve circular polarization for HF skip communication. A
second problem is that the majority of CP antennas, such as the
quadrature fed crossed dipole "turnstile", are circular only directly
broadside, and increasingly elliptical as you move away from that direction.

Roy Lewallen, W7EL

On Mon, 10 Aug 2009 11:44:52 -0700, Roy Lewallen
wrote:

I also did some experiments in the early '70s to see if CP would reduce
fading. I built a couple of types of omnidirectional CP antennas -- a
"skew planar", and a copy of a commercial FM BC antenna, for mobile use
with the local 450 MHz repeater.

A "halo" type of antenna? Some of the commercial broadcast FM
antennas are eliptical polarized. Most of the signal is horizontally
polarized, but there is a small vertical component in order to improve
performance in vehicles.

We tried several antennas at the repeater end. Something like this
one seemed to work best:
http://iris.nyit.edu/~sblank/VPFMfig5.gif
We had 4 elements with a coax cable phasing mess.

I soon discovered that as soon as I
placed the antenna over the top of the car, the polarization became
nearly linear. I've since learned that it's because of the nature of the
reflections from the ground plane, and it's easily seen with EZNEC+.
When I put the antenna far enough away from the car to minimize
reflections, the lowered gain offset any possible advantage. Overall,
they worked out worse than a conventional vertically polarized antenna.

I tried to use CP on both ends and eventually gave up. Thanks for the
explanation, but I have a different theory. The polarization changes
sense (direction) every times it's reflected. We standardized on RH
CP. When the RH CP signal hits the car, it is reflected as LH CP. If
the LH CP signal arrives at the repeater antenna, which is RH
polarized, they cancel. If it became linear, it would theoretically
only present a -3dB polarization loss, which is not huge.

It might have been interesting to try CP at the repeater, but that was
never done.

I can testify that it worked quite well for solving the specific
problem. We were trying to eliminate picket fencing (frequency
selective fading or Rayleigh fading). While there were some half
hearted experiments with various CP mobile antennas, the major effort
was at the repeater end. This was about 1971 so the technology used
was rather crude. One student was doing his senior project (reqd for
graduation) around this test. Several of us were enlisted to help.
When was in the land mobile radio biz many years later, I repeated the
tests with similar results.

We hung a thermal chart recorder onto the first limiter testpoint (on
a Motorola Sensicon T43 receiver) and plotted signal strength versus
time as a mobile drove through the problem area with the xmitter keyed
continuously. The test was repeated with various tower mounted
antennas. The linear antenna had more signal (gain) than CP, but also
had many more fades, what were far more pronounced. In all, I would
call it an improvement in quality, but not in range.

The problem with ground reflection ruining the circularity makes it very
difficult to achieve circular polarization for HF skip communication.

Well, I supplied several examples of commercial HF antennas that are
circularly polarized. I'm tempted to try building one, just to see
what works or breaks.

A second problem is that the majority of CP antennas, such as the
quadrature fed crossed dipole "turnstile", are circular only directly
broadside, and increasingly elliptical as you move away from that direction.

That's why high accuracy GPS antennas use choke rings at the antenna.
It widens the pattern so that it picks up more of the sky, but also
maintains some semblence of CP at the horizon.

Any interest in me scanning and posting the chapter on circular
polarization repeater antennas from the TAB book? 13 pages with some
low quality pictures.

Roy Lewallen, W7EL

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

"Art Unwin" wrote in message
...
The majority of antennas used today are (commercial) circularly polarized


That probably isn't true for VHF/UHF. Take a look at the website of a major
supplier of professional antennas such as
http://www.amphenol-jaybeam.com/base...nas-search.php. Entering
CP in their search engine for base-station antennas yielded 2 results wheras
entering VP yielded 365!

One of the reasons for greater use of linear polarisations in professional
applications is frequency re-use on the orthogonal polarisation some
distance away - i.e. the value of the limited VHF/UHF spectrum. That's
certainly true in Europe.


Ham antennas remain in the linear domain (ala the Yagi and similar)
There are many reasons espoused in CP advantages in "point to point"
What is the main advantage hams hold over the more popular circular
polarized antennas in its "skip" type useage versus "point to point" ?


Extensive use is made of 'mixed polarisation' for transmitting VHF FM
broadcast services in Europe. It may not be pure circular but it contains
significant vertically- and horizontally-polarised components. The mobile
and portable receiving antennas have whatever polarisation they end up with,
more or less by accident, and fixed rooftop antennas are usually linearly
polarised. DAB and terrestrial television are transmitted using V or H
linear polarisation.

Chris