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firebat
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Joined: Mon Apr 11, 2005 8:38 am

Antenna help needed

Tue Apr 03, 2007 8:39 am

We are deploying are first Mikrotik hotspot in a rural town and are having issues. We are using a Ubiquiti SR2 on a RB532A with a Pac Wireless 2.4 12DBi v-pol omni with 3 degree downtilt. We tested the AP with the antenna at 10FT and it seemed to be working OK. We then installed it on top of a building at a height of about 35' and we get very poor connections everywhere within the down (mile radius). We swapped the hole unit out with another one (mikrotik Hardware and antenna) and same result. The antenna is on a 10FT mast on top of a building with a very slight pitch and is about 5 feet from the front edge. The building has a metal roof. There is a Canopy 2.4 AP about2.5 miles away pointed toward the town but we tried several frequencies and had the same problem. I think we may be overshooting the town. The Beamwidth of the omni is 8 degrees.

Should we switch to a 7 or 9 DBi antenna to significantly increase the beamwidth? Would it be better to run sectors on each edge of the building? Are there any issues with installing multiple SR2s or RB52s on a single Routerboard?
 
pedja
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Thu Apr 05, 2007 1:21 pm

You are probably overshooting with signal. Check out online calculator for antenna gray zone at http://wireless.uzice.net/uputstvo-odre ... antene.htm. check the bootom of page.

It is not in english, but I guess you would be able to handle as all formula items are clearly marked on pictures.

For your situation: height of antenna (h) = 35 ft, vertical radiation angle (α) = 8° and no tilted antena, gray zone (l) expands up to 501 ft from antenna. If you tilt antena (ß) 5° toward clients, gray zone shrinks to 221 ft.

Using calculator is simple, fill in three known values and click buton to calculate foruth value.

By the way, tilting omni antena is wasting energy. You get grayyone shrinked n tilted side,but on other side you just send energy into the sky. If you need tilting, always use sector antenna, not omni.
 
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dibatech
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Antenna

Thu Apr 12, 2007 7:52 pm

The antenna radiates in a narrow 8 degree angle on the y-axis.(Vertical)
It should work better to get a lower gain sectorized antenna that has a smaller beamwidth for example 90 degree -3dB instead of a 120 degree unit.
You should then be able to tilt your antenna further down, but still cover further areas as the lobe on the y-axis of a narrower sectorized is usually bigger. (I'm guessing 12 - 15 degrees)

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