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  #1 (permalink)  
Old 12-26-2006, 01:47 AM
PrvtPilot
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Default Horizontal And Vertical Antennas

Hi,

I am setting up a small wireless network that will have to cover a bit
of distance. I have a 40 foot tall tower and clear shots to the
buildings I have to get to.

I am mounting two antennas on top of the tower, one horizontal and one
vertical polarized antennas.

My question, is there a standard as far as antenna placement using a
configuration like this? Distance apart? Should one be higher than the
other? I will be using a Proxim AP-4000 to run the show and have been
told that a 1 watt amp on each antenna would be a good thing. Still
wondering about that.

Anyway, I am new to this and would like to get this straight.

Thanks,
Dean


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  #2 (permalink)  
Old 12-26-2006, 02:58 AM
Dana
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Default Re: Horizontal And Vertical Antennas


"PrvtPilot" <drichards@draoidh.com> wrote in message
news:1167101222.809630.43180@48g2000cwx.googlegrou ps.com...
> Hi,
>
> I am setting up a small wireless network that will have to cover a bit
> of distance. I have a 40 foot tall tower and clear shots to the
> buildings I have to get to.


Sounds good.
>
> I am mounting two antennas on top of the tower, one horizontal and one
> vertical polarized antennas.


Great idea if the price is right.
>
> My question, is there a standard as far as antenna placement using a
> configuration like this? Distance apart? Should one be higher than the
> other?


Excellent questions.
Typically you would have antennas separated by "X" number of feet (with your
accent maybe I should say meters), dependent on the frequency being used.
But since you are using two different polarizations you will have isolation
between them already.
For antenna placement of the same polarity, you can get away with less
vertical separation between antennas as you would with Horizontal separation
(for most directional antenna).
Here is a link that will calculate the isolation you will get for the
separation between the antennas.
http://my.athenet.net/~multiplx/cgi-...ation.main.cgi

http://pacwireless.com/support/Antenna_Isolation.pdf

For horizontal separation you can use
22+20log(d/ f) - (G1+G2) - (S1+S2)
d = distance
f = freq
g1 and g2 are the main lobe gains of the antenna
s1 and s2 are the side lobe levels of the antenna

For vertical separation you can use
28+40log(d/f)
d = distance
f = freq

From experience and at the freq you will be using 3 feet vertical and 4 feet
horizontal separation should be good to go (1 meter vertical, and say 1.5
meter horizontal)


>I will be using a Proxim AP-4000 to run the show and have been
> told that a 1 watt amp on each antenna would be a good thing. Still
> wondering about that.


So long as you do not violate any emission standard from your FCC type
people should not be a problem. This depends also on the gain of your
antenna, and how far you are trying to go.
>
> Anyway, I am new to this and would like to get this straight.


Seems you are asking the correct questions.

Have you looked into any cross pol antennas.

>
> Thanks,
> Dean
>




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  #3 (permalink)  
Old 12-27-2006, 04:52 PM
PrvtPilot
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Default Re: Horizontal And Vertical Antennas

Thanks for the great information,

Dana wrote:
> So long as you do not violate any emission standard from your FCC type
> people should not be a problem. This depends also on the gain of your
> antenna, and how far you are trying to go.


I am in the San Fransisco Bay Area, I will check to see what the FCC
has to say about the power output before I put any amps to the system.

The Horizontal antenna is 12 dB and the Vertical is 15.4 dB. I am
looking to cover about 3/4 of a mile with this setup. The AP-4000
output is about 18-20dB if I read the spec sheet correctly.

Dean


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  #4 (permalink)  
Old 12-27-2006, 10:54 PM
Jeff Liebermann
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Default Re: Horizontal And Vertical Antennas

On 25 Dec 2006 18:47:02 -0800, "PrvtPilot" <drichards@draoidh.com>
wrote:

>I will be using a Proxim AP-4000 to run the show and have been
>told that a 1 watt amp on each antenna would be a good thing. Still
>wondering about that.


No doubt, the salesman that's selling overpriced 1 watt amplifiers
toly you it would be a good thing. The AP-4000 already belches +20dBm
(100mw). The AP-4000 is also a dual band access point, therefore
requiring an amplfier for each band. The AP-4000 also support PoE
meaning you install it in a waterproof box on the tower near the
antenna.

The problem with amplifiers is that excessive power on one end of a
wireless link creates an "alligator". That's an animal with a big
(transmit) mouth, and small (receive) ears. Your AP-4000 will be
heard over a much larger areas than it can hear. If your clients are
using +17dBm (35mw) MiniPCI cards inside laptops, your AP-4000 isn't
going to hear them at extreme range. I consider such systems not much
better than a jammer. Try to keep the EIRP fairly symmetrical, so you
don't create this problem.

The best way to extend coverage is with antenna gain. The range
improvement is symmetrical, unlike the aformentioned alligator.

Dana explained the antenna positioning calculations clearly. I've had
isolation problems that could only be solved by installing some wire
screening between the antennas. Much of the leakage came from bounces
off of the tower, coax cables, back of other WISP's dishes, etc.



--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558 jeffl@comix.santa-cruz.ca.us
# http://802.11junk.com jeffl@cruzio.com
# http://www.LearnByDestroying.com AE6KS

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  #5 (permalink)  
Old 12-28-2006, 04:19 AM
Dana
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Default Re: Horizontal And Vertical Antennas


"PrvtPilot" <drichards@draoidh.com> wrote in message
news:1167241976.225360.232210@a3g2000cwd.googlegro ups.com...
> Thanks for the great information,
>
> Dana wrote:
> > So long as you do not violate any emission standard from your FCC type
> > people should not be a problem. This depends also on the gain of your
> > antenna, and how far you are trying to go.

>
> I am in the San Fransisco Bay Area, I will check to see what the FCC
> has to say about the power output before I put any amps to the system.
>
> The Horizontal antenna is 12 dB and the Vertical is 15.4 dB. I am
> looking to cover about 3/4 of a mile with this setup. The AP-4000
> output is about 18-20dB if I read the spec sheet correctly.
>
> Dean


Hi, glad to be of help. Even though the equipment you are using is supposed
to be unlicensed, the FCC still limits how much power can be radiated.
And this limit is usually specified after the gain of the antenna, basically
what is called the EIRP, which is the output of your transmitter, minus the
feedline loss, plus the gain of your antenna.
Jeff also gave a more detailed explanation of the power concern, so I will
not repeat that here.



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