As a rule of thumb, as the dB gets higher(or smaller in negative speak) in an antenna, the beam width of the opposing polarity of the antenna gets smaller, and thus harder to work with.
As an example, I have used 15dB Omni's in 2.4Ghz(I'll leave the brand unannounced). I first put them about 60 feet in the air and found that I could not get a good usable signal unless I was about 2 miles or so from the tower. I dropped them to 20 - 25 feet and picked up clients within .25 miles out to a couple of miles. The horizontal beam width on the Omni was so small, I was way overshooting my intended target. Lesson learned was to always look at both vert and horiz beam width, and lesson learned on the 15dB Omni is to only use in trailer parks, very small subdivisions, and RV parks... and ... to not mount it above 30 feet high. Scottie ---------- Original Message ---------------------------------- From: "Robert West" <[email protected]> Reply-To: WISPA General List <[email protected]> Date: Mon, 29 Mar 2010 18:41:21 -0400 >Well, I've been setting up a service contract with my friends on planet >Wispalon so I need to find the proper tilt angle to beam the signal into >space. :) > >Yeah, I've been mindful to stay off the horizon, seems wasteful in a big >way. I'm not a trig scholar so I use basic tilt angle calculators which >have never failed me but these things have me upside down. Tower height, >distance desired and all are good to have but I was really interested in >others experiences with them and how they have been able to get their >angles. Again, the smaller, lower gain sectors have been right on the money >but I wasn't aware (ignorant) that these high gain units would give me a >smaller slice to work with. On the advice of another member I have been >trying one AP with 4 120 degree 19dbi sectors used as 90's. Signal is great >where we can see it, just needed a good fix for not having to do the 2 man >show all over the county. (With everyone in a pickup truck stopping to ask >why we're by the road with an antenna) > >Bob- > > >-----Original Message----- >From: [email protected] [mailto:[email protected]] On >Behalf Of Lawrence E. Bakst >Sent: Monday, March 29, 2010 5:50 PM >To: WISPA General List >Subject: Re: [WISPA] Ubiquiti Sector Tilt angle > >Technically speaking you're wrong. The highest gain area of a sector antenna >is the center point between the horizontal and vertical spreads. If you >don't downtilt you are sending the strongest part of the signal parallel to >the horizon. Why would you ever want to do that? The whole reason you >downtilt is to get the strongest signal pointed to the area you want. > >Figuring this out takes some basic trig calcs using the tangent function. > >No one has asked the most important questions you need to know when >calculating downtilt: > >1. How high up is the sector antenna? > >2. How far out or in what range near to far do you want the sweet spot? > >3. How close in to the tower do you need service? > >#2 and #3 can conflict with each other and you may have to make a tradeoff. > >leb > >At 2:22 PM -0400 3/29/10, Faisal Imtiaz wrote: >>..... Technically speaking.. if you are not concerned about dealing with >>'near' customers.... less than 1 or 2 miles... then you can pretty much >>leave the sectors at '0' tilt.. and you have coverage to the horizon.... >> >>The built-in electrical down-tilt typically throws folks off...... only >>becomes a factor if you are needing to down tilt for near customers.. >> >>Faisal. >> >>On 3/29/2010 1:36 PM, Robert West wrote: >>> I'm having a heck of a time with the large UBNT sectors getting the tilt >>> angle to jive. With the smaller sectors, they behave perfectly and go >right >>> where the calculations say they will however, with the larger ones, >nothing >>> I do other than have someone 10 miles out with a CPE check levels while I >>> tilt up and down seems to be good. I REALLY don't want to have to do >that >>> with all of them... >>> >>> >>> >>> Anyone having any success or insight with the proper tilt of these >things? >>> Using the 120 degree 5GHz flavors. >>> >>> >>> >>> Thanks! >>> >>> >>> >>> Robert West >>> >>> Just Micro Digital Services Inc. >>> >>> 740-335-7020 >>> >>> >>> >>> Logo5 >>> >>> >>> >>> >>> >>> >>> >>> >>> >>> >---------------------------------------------------------------------------- >---- >>> WISPA Wants You! Join today! >>> http://signup.wispa.org/ >>> >---------------------------------------------------------------------------- >---- >>> >>> WISPA Wireless List: [email protected] >>> >>> Subscribe/Unsubscribe: >>> http://lists.wispa.org/mailman/listinfo/wireless >>> >>> Archives: http://lists.wispa.org/pipermail/wireless/ >> >> >>--------------------------------------------------------------------------- >----- >>WISPA Wants You! 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