I'm following this thread trying to pick up a general rule of thumb to start out with for down tilt (I have 2.4 systems though).
I've seen three different methods of calculating it specified. 1). Downtilt enough so all your customers fall within the main lobe's -3 db line. 2). Downtilt so that your beam is focused half-way to your recommended coverage. 3). Downtilt so that you reach the furthest customer in your projected coverage area. These all seem mutually exclusive, unless I'm missing something. Regards Michael Baird > I disagree, Precise Tilt does matter quite a bit with Tiltek 900Mhz > sectors. > > Let me give an example of mounted at 400ft with Tiltek sectors having 17 deg > vert beamwidth. > > 8 deg downtilt, min .25 miles, max horizon. > > 9 degree downtilt, min .24 miles, max 8.6 miles. > > 10 degree downtilt, Min distance .22 miles, Max distance 2.8 miles. > > 11 deg downtilt, min .21 miles, Max 1.7 miles > > Near field coverage is rarely a problem with 900Mhz, regardless of the tilt. > But what people forget is how much the far field is effected by just a > single degree. > > The difference between 9 versus10 degrees is the difference of "5 miles !" > coverage at optimal signal strength. > The difference between 8 versus 10 degrees is the difference of whether you > interfere with your other towers 30 miles away versus 3 miles away. > > With 900Mhz, EVERY DB counts. The reason is two fold. 1) The noise floor is > ften high. 2) Its very easy to get colocated AP antenna self interference, > when foliage can degrade the signal of a single link severally. For example, > the Front-to-back isolation loss could be equivellent to the loss of foliage > in a path. > > The goal is to get the highest signal uniformally to the largest area within > your desired coverage area. Then you can always lower CPE transmit power as > needed on links without foliage loss. In my 900 deployments, I have found > that 3db lost or gained can be the difference between a typically good > versus bad link. > > Now, its true the above beamwidths are only the distances that show "3 db" > loss, so a 10 degree downtilt, sector will still have a significant amount > of signal going out to and heard from the the horizon. But every DB counts. > > The critical question becomes do you mount high or not? Higher avoids more > trees. HIgher hears more interference. We found what was best for us was to > go higher, but add more downtilt. We shoot for 10 degree downtilt. But it > can be a delicate balance, dependent on your environment and noise levels > and locations. We will usally put a larger focus on reducing noise to our > adjacent cell sites, even if at the cost of gain to our intended coverage > area. > > Tom DeReggi > RapidDSL & Wireless, Inc > IntAirNet- Fixed Wireless Broadband > > > ----- Original Message ----- > From: "Cliff Olle" <w...@eccentrixtechnologies.com> > To: "'WISPA General List'" <wireless@wispa.org> > Sent: Monday, March 09, 2009 9:25 PM > Subject: [WISPA] 900 Downtilt at 300' > > > >> For the 900 Mhz connectorized AP (by cyclone) with the 120 tiltek antenna, >> if I am mounted at 300', what amount of down tilt is normal? >> >> >> >> -------------------------------------------------------------------------------- >> WISPA Wants You! Join today! >> http://signup.wispa.org/ >> -------------------------------------------------------------------------------- >> >> WISPA Wireless List: wireless@wispa.org >> >> Subscribe/Unsubscribe: >> http://lists.wispa.org/mailman/listinfo/wireless >> >> Archives: http://lists.wispa.org/pipermail/wireless/ >> >> >> -- >> No virus found in this incoming message. >> Checked by AVG. >> Version: 7.5.557 / Virus Database: 270.11.9/1991 - Release Date: 3/9/2009 >> 7:14 AM >> >> >> > > > > -------------------------------------------------------------------------------- > WISPA Wants You! Join today! > http://signup.wispa.org/ > -------------------------------------------------------------------------------- > > WISPA Wireless List: wireless@wispa.org > > Subscribe/Unsubscribe: > http://lists.wispa.org/mailman/listinfo/wireless > > Archives: http://lists.wispa.org/pipermail/wireless/ > -------------------------------------------------------------------------------- WISPA Wants You! Join today! http://signup.wispa.org/ -------------------------------------------------------------------------------- WISPA Wireless List: wireless@wispa.org Subscribe/Unsubscribe: http://lists.wispa.org/mailman/listinfo/wireless Archives: http://lists.wispa.org/pipermail/wireless/
