The nicer the antenna, the more critical the aim is. A cheap 900 sector will create a forgiving coverage pattern. A nice one like Tiltek or MTI will have a well defined coverage pattern in the vertical direction.
Personally, I wouldn't put 900 that high on a tower, as it would receive too much interference in my areas. I'd be hesitant to put 900 over 150 feet. But anything going that high up should be a high quality antenna, anything else is false economy in the event it needs repair or replacement. On Tue, Mar 10, 2009 at 12:42:57AM -0400, Tom DeReggi wrote: > 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" <[email protected]> > To: "'WISPA General List'" <[email protected]> > 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: [email protected] > > > > 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: [email protected] > > Subscribe/Unsubscribe: > http://lists.wispa.org/mailman/listinfo/wireless > > Archives: http://lists.wispa.org/pipermail/wireless/ -- /* Jason Philbrook | Midcoast Internet Solutions - Wireless and DSL KB1IOJ | Broadband Internet Access, Dialup, and Hosting http://f64.nu/ | for Midcoast Maine http://www.midcoast.com/ */ -------------------------------------------------------------------------------- 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/
