antenna diversity?

When looking at install an outdoor antenna what are the issues associated
with spatial and/or polarization diversity?

For example, hyperlink sells two panel antennae, one with 'spatial' and the
other with 'polarization' diversity.

http://sharperconcepts.zoovy.com/product/YSC-RE11DP
http://sharperconcepts.zoovy.com/product/YSC-RE11DS

Under what conditions would one be better/worse than the other?

Thanks,
-Bill Kearney

On Wed, 19 Jul 2006 13:23:45 -0400, "Bill Kearney"
<(E-Mail Removed)> wrote:

>When looking at install an outdoor antenna what are the issues associated
>with spatial and/or polarization diversity?

The diversity algorithm used by your radios has a big effect.
http://img.cmpnet.com/commsdesign/cs...eat1-jan03.pdf

>For example, hyperlink sells two panel antennae, one with 'spatial' and the
>other with 'polarization' diversity.
>
>http://sharperconcepts.zoovy.com/product/YSC-RE11DP
>http://sharperconcepts.zoovy.com/product/YSC-RE11DS
>
>Under what conditions would one be better/worse than the other?

They're about equal. The main problem that both of these are really
good at eliminating is frequency selective fading. This is where you
have two paths to a given single antenna. The two paths are exactly
180 degrees out of phase resulting in a deep null at one frequency.
Chances are really good that a null at one antenna will not also
appear at the other antenna.

However, there's no way to optimize either the location (spatial) or
the polarization of the two signals. The probability that they might
cancel at any given point is fairly independent of the antenna
construction and configuration. As long as there is more than one
path to a given antenna, there will be nulls and cancellation. It
really depends more on the room under test. I suppose I could
contrive an artificially weird room that is polarization or location
sensitive, but that's not reality. For example, if you're shooting
over water, spatial would definitely be better because there's only
one place for the signal to bounce and it's going to be the same
polarization as the original.


--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558 (E-Mail Removed)
# http://802.11junk.com (E-Mail Removed)
# http://www.LearnByDestroying.com AE6KS

> For example, if you're shooting
> over water, spatial would definitely be better because there's only
> one place for the signal to bounce and it's going to be the same
> polarization as the original.

Hmmm, what about being in a marina amongst both power and sailboats?

On Wed, 19 Jul 2006 23:33:22 -0400, "Bill Kearney"
<(E-Mail Removed)> wrote:

>> For example, if you're shooting
>> over water, spatial would definitely be better because there's only
>> one place for the signal to bounce and it's going to be the same
>> polarization as the original.

>Hmmm, what about being in a marina amongst both power and sailboats?

The (near) vertical sheets and vertical masts will do a marvelous job
of generating vertical polarized reflections while somewhat blocking
horizontal reflections. The relatively wide masts will reflect some
horizontally polarized signals (because they're about a wavelength
across), but not as much as the verticals.

I would guess(tm) that spacial diversity with the antennas vertically
polarized would be best on the assumption that most of the usable
signals will be vertical. However, there will be fewer reflections in
the horizontal so maybe the horizontal is better. Argh... decisions.

One thing for sure, there's no need to do polarization diversity.
There will be far more usable signal with vertical polarization than
with horizontal. Maybe if you put the two antennas at opposing 45
degree angles? That might be useful. Argh... decisions.

Can I give up while I'm still sane?


--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558 (E-Mail Removed)
# http://802.11junk.com (E-Mail Removed)
# http://www.LearnByDestroying.com AE6KS

> One thing for sure, there's no need to do polarization diversity.
> There will be far more usable signal with vertical polarization than
> with horizontal. Maybe if you put the two antennas at opposing 45
> degree angles? That might be useful. Argh... decisions.
>
> Can I give up while I'm still sane?

Wait, you're arguing you're sane now? <grin>

Then how about putting up one at a 45 degree angle? <grin, again>

I'll go with the spatially diverse one instead of the one with polarization
then.

Thanks,
-Bill Kearney