Direction Antenna Question

Direction Antenna Question

Postby systemd0wn » Tue Sep 03, 2002 10:42 am

Allright with the attached image, would the stumbler in the car be able to pick up the AP? I didnt think it would be able to, but then i started doubting myself. so im asking :)
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Postby Thunderforge » Tue Sep 03, 2002 10:53 am

No. None of the APs transmissions would hit the card.
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A Definite "Maybe"

Postby Thorn » Tue Sep 03, 2002 10:53 am

The stumbler probably would not pick up the AP under most circumstances.

However, if they were close enough or the hit a side-lobe of the radiating pattern, they might. It would also depend on the model of directional, beam width, etc, etc...
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Postby tabasco » Tue Sep 03, 2002 11:00 am

My guess would be yes. The Directional dish focuses the beam in a direction however there is still going to be signal radiated in all direction. Granted the signal may not travel as far in then non-beam directions as with an Omni but it will still be bleeding a little signal.

Think of it this way.

If you look at your headlights from the front in the beams path it will be very bright however all the light is not focused in that direction. If you stand to the side of the beam you will still see light and the fact that it is illuminating objects not in the Beams path. All though its not as bright there is some significant light/signal loss.

Even if you use a “Laser” which is a very focused beam of light (much like using a Wave Guide) there will still be some ambient light/signal.

One thing to keep in mind is “How Tall is that Tower?” If the tower is too tall, there many not be enough ambient signal to reach the ground.

Of course I may be wrong
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Postby Thunderforge » Tue Sep 03, 2002 11:07 am

I read his question as a more theorhetical "does the AP have to be in the transmission path of my card or vice versa to see the AP?" type inquiry. Their is always some bleed of the signal but without actual measurements and equipment lists it would be difficult to say they will always see it. From the picture you couldn't guarentee coverage.
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Postby Thorn » Tue Sep 03, 2002 11:10 am

Originally posted by Thunderforge
I read his question as a more theorhetical "does the AP have to be in the transmission path of my card or vice versa to see the AP?" type inquiry. Their is always some bleed of the signal but without actual measurements and equipment lists it would be difficult to say they will always see it. From the picture you couldn't guarentee coverage.


Exactly. Which is why I said what I did. ;)
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Postby tabasco » Tue Sep 03, 2002 11:13 am

Thunderforge is very right. What the Beam "Should" do is go right over your head.
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Postby systemd0wn » Tue Sep 03, 2002 12:09 pm

aight, i figured that if could it would either be using those side-lobes of the radiating patern. OR i would be close enough to get a "bleed off" if you will. Anyway, thanks guys :) ill have to actualy test this out some time. its not actualy a tower (it was easier to draw though :) ) its just as high as the roof of a 1 story building.
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Postby ted » Tue Sep 03, 2002 7:50 pm

I interprete that this is one end of a point-to-point link, with highly directional parabolic antenna(s).

Being close enough, the sidelobes and maybe even leakage of the feeder are (possibly) detectable. However, moving the stumbler just a little may vary the signal from zero to descent and back to zero. Nothing reliable even when on it's best, don't count on it.

But another interesting aspect: The stumbler might receive signal from the other end of that point-to-point link due to reflections from the antenna structure. Depending who is the access point and who is the client -- or maybe both in ad-hoc -- you either see the one or another. Usually the signal level of such reflected remote transmission would be too low, but if the link has solid margins, maybe...
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