On Feb 15, 11:01*am, Art Unwin wrote:
On Feb 14, 11:26*pm, Jeff Liebermann wrote:



On Sun, 14 Feb 2010 20:51:21 -0800 (PST), Art Unwin

wrote:
Has there ever been a study *that shows the relative consistency of
received signal polarity to see if it would be advantageous for multi
polarity receive antennas?

Yes. *I did one for a company doing exactly that at various
frequencies between 120 to 450Mhz. *Sorry, but I don't have a copy of
the report. *For convenience, we use ham frequencies for most of the
testing. *What we found is that once a signal is reflected, the
reflected signals polarization is fairly random. *There are few flat
plate reflectors in both man made and natural objects. *The measured
result was a mess of varying polarization angles.

You can expect similar results for HF signals reflected off the
ionosphere with the added complexity of Faraday rotation.

However, it is beneficial to build polarization insensitive antennas.
In a common dipole, there's very little loss for polarization mismatch
until you get very close to perpendicular. *There, the signal drops
off quickly. *Filling in this hole is considered to be a good thing.

You can get a crude idea of how it works using an Adcock DF antenna
array, or just two cross polarized dipoles. *Since you're not building
a direction finder, the crossed dipoles are easier to explain. *Just
setup two perpendicular dipoles with the center feeds fairly close
together. *Connect two well matched receivers to the two antennas.
Connect the IF or audio outputs to the vertical and horizontal of an
oscilloscope. *The resulting Lissajous pattern will give you a rough
idea of the polarization (assuming the signal arrives from above).
Pick a strong steady signal like WWV. *You'll probably see the
polarization change erratically when the skip is in. *(Last time I did
this was 20 years ago). *You'll also see that vertical and horizontal
parts of the Lissajous display to wander around in amplitude fairly
independently. *This is the main advantage of a polarization
independent antenna. *The antenna will automagically select the
strongest polarization to feed the receiver.

There are circularly polarized HF antennas, but I'm too lazy to Google
for them tonite.

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

Thank you for that!
I have not seen the like printed any where soto me *it is good stuff.
When I model a polarization independent antenna the individual gains
confuse me as each of the individual gains are some what 3 db down
from the "total" gain. In other words "total" is not the addition of
all the polarizations gains. I find it very difficult to get my mind
wrapped around that fact. On the surface it would suggest that
competition types would benefit from a polarization independent
antenna.

What is/are "polarizations gains". That's a term with which I am not
familiar.

Jimmie

On Mon, 15 Feb 2010 14:07:35 -0800 (PST), JIMMIE
wrote:

On Feb 15, 11:01*am, Art Unwin wrote:
I have not seen the like printed any where soto me *it is good stuff.
When I model a polarization independent antenna the individual gains
confuse me as each of the individual gains are some what 3 db down
from the "total" gain. In other words "total" is not the addition of
all the polarizations gains. I find it very difficult to get my mind
wrapped around that fact. On the surface it would suggest that
competition types would benefit from a polarization independent
antenna.

What is/are "polarizations gains". That's a term with which I am not
familiar.

Jimmie

It's part of Polarity Therapy:
http://en.wikipedia.org/wiki/Polarity_therapy
I think it has something to do with yin and yang polarization.
Applying acupuncture to the coax cable is known to activate and
improve the flow of Chi, as well as increase the life force energy,
which is what produces the necessary gain.

(Sorry, I couldn't resist).

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

On Mon, 15 Feb 2010 14:07:35 -0800 (PST), JIMMIE
wrote:

What is/are "polarizations gains". That's a term with which I am not
familiar.

Hi Jimmie,

EZNEC, for one, reports antenna "gain"/directivity (re dBi) for each
polarization, azimuthum or elevation; or their sum as a total field
for a 3D model.

When two antennas (one receive, one transmit) are cross polarized, the
gain between them can vanish to zero. In a real application this zero
is something larger, but still small like 30dB down compared to two
antennas employing the same polarization.

This last is observed in line of sight transmissions of VHF and above
(try hitting your favorite 2M repeater with the wrong antenna
polarization orientation). It is not so common at HF as long paths
(aka skip) can blur the polarization (as can nearby reflectors for any
frequency) causing intermittant fading.

73's
Richard Clark, KB7QHC

On Feb 15, 6:38*pm, Richard Clark wrote:
On Mon, 15 Feb 2010 14:07:35 -0800 (PST), JIMMIE

wrote:
What is/are "polarizations gains". That's a term with *which *I am not
familiar.

Hi Jimmie,

EZNEC, for one, reports antenna "gain"/directivity (re dBi) for each
polarization, azimuthum or elevation; or their sum as a total field
for a 3D model.

When two antennas (one receive, one transmit) are cross polarized, the
gain between them can vanish to zero. *In a real application this zero
is something larger, but still small like 30dB down compared to two
antennas employing the same polarization.

This last is observed in line of sight transmissions of VHF and above
(try hitting your favorite 2M repeater with the wrong antenna
polarization orientation). *It is not so common at HF as long paths
(aka skip) can blur the polarization (as can nearby reflectors for any
frequency) causing intermittant fading.

73's
Richard Clark, KB7QHC

A different perspective on polarization loss?

Jimmie

On Mon, 15 Feb 2010 19:04:51 -0800 (PST), JIMMIE
wrote:

A different perspective on polarization loss?

Different? How? All pretty standard stuff.

As for different literal perspectives of polarization, I am sitting
here with two sets of 3D glasses for "Avatar" (just got back from the
IMAX version) and these two pair of glasses are very different from my
experience with Polaroid lenses of days gone by. And they are very
different from each other for the same movie.

The Real3D glasses at IMAX didn't work as normally worn, I still saw a
double image; but viewing the movie through the lenses backwards (ear
pieces going forward) rendered the IMAX 3D as 2D.

Now, when I sit here at the console and view the display (flat screen)
through the IMAX lenses, I can dim the display by rotating the pair.
One eye piece goes black at 45 degrees rotation, and the other eye
piece goes black at -45 degrees rotation. Flip them to look through
them backwards, and the same effect is observed.

When I take the Real3D pair and rotate them, only a slight shift in
hue: yellow tint in both lenses at 45 degrees rotation, and a blue
tint at -45 degrees rotation. When I flip them to look through them
backwards, I encounter a slight brightening for both lenses at 45
degrees rotation and a complete blocking for both lenses at -45
degrees.

I am familiar with display technology employing LCDs with double
polarization to increase contrast, and I could easily expect this from
the lenses of these two pairs of 3D glasses. Without having gone
further into researching it, I have a hunch that I am encountering
circular polarization here.

A little digging will tell.

73's
Richard Clark, KB7QHC

On Mon, 15 Feb 2010 22:44:13 -0800, Richard Clark
wrote:

Without having gone
further into researching it, I have a hunch that I am encountering
circular polarization here.

Yep. RealD XL 3D is circularly polarized:
http://en.wikipedia.org/wiki/RealD_Cinema
http://en.wikipedia.org/wiki/List_of_RealD_films

"How to avoid getting a 3D headache while watching Avatar"
http://www.shadowlocked.com/index.php?option=com_content&view=article&id=70:ho w-to-avoid-getting-a-3d-headache-while-watching-avatar&catid=41:feature




--
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 Liebermann wrote:
On Mon, 15 Feb 2010 22:44:13 -0800, Richard Clark
wrote:

Without having gone
further into researching it, I have a hunch that I am encountering
circular polarization here.

Yep. RealD XL 3D is circularly polarized:
http://en.wikipedia.org/wiki/RealD_Cinema
http://en.wikipedia.org/wiki/List_of_RealD_films

"How to avoid getting a 3D headache while watching Avatar"
http://www.shadowlocked.com/index.php?option=com_content&view=article&id=70:ho w-to-avoid-getting-a-3d-headache-while-watching-avatar&catid=41:feature





Which makes perfect sense, since it means that if you tilt your head,
you don't swap images between left and right eyes. A very clever use of CP.

Model of 2 element multi polarization.

http://users.sdsc.edu/~unwin/art/Picture6.png
http://users.sdsc.edu/~unwin/art/Picture7.png
http://users.sdsc.edu/~unwin/art/Picture10.png
http://users.sdsc.edu/~unwin/art/Picture11.png