Circular versus linear polarization
 

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" ?

Circular versus linear polarization
 

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

Circular versus linear polarization
 

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

Circular versus linear polarization
 

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.

Circular versus linear polarization
 

"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

Circular versus linear polarization
 

On Aug 10, 9:04*am, "christofire" wrote:
"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 ashttp://www.amphenol-jaybeam.com/base-station-antennas-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

Hmm A bit too technical for me! When I model my antennas it
shows gain for cp being 3 db above the gains of vertical and
horizontal for the same antenna. Is that what you call "mixed
polarization? In other words, it picks up all polarizations with a
max deviation in signal strength of only 3 db.
I find it hard to make any sort of comparison when using reflective
waves at HF because it is not clear to me exactly what sort of
rotations occur at the reflections on earth and of its layers
together with possible rotation in transit in between in the absence
of true comparison experiments.

Circular versus linear polarization
 

christofire wrote:
"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


Off subject I know but as a matter of interest what happens to a TX CP
antenna with a clockwise twist transmitting to a RX CP antenna with an
anticlockwise twist, over short to medium vhf/uhf paths, I would have
thought a reduction in signal ?

Pedr GW6YMS

Circular versus linear polarization
 

"P.R.Humphreys" wrote in message
...
Off subject I know but as a matter of interest what happens to a TX CP
antenna with a clockwise twist transmitting to a RX CP antenna with an
anticlockwise twist, over short to medium vhf/uhf paths, I would have
thought a reduction in signal ?

Pedr GW6YMS

About the same as going from a horizontal to a vertical antenna. You loose
about 20 db of signal.
One thing a CP signal will do that a horizontal or vertical signal won't is
to reverse when it bounces off an object. That is if you are doing moon
bounce and send up a signal using right hand CP , your receiving antenna
will need to be left hand CP or you loose lots of db of signal.

Also on the satellites it is helpful to be able to change the CP from left
to right as the signal sometimes reverses depending on the angle the
satellite antenna is pointing as it passes over.

Circular versus linear polarization
 

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.

Circular versus linear polarization
 

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