Tom, that's option 1, which I think you suggested earlier, and why I put it on my list.
1). Downtilt enough so all customers fall within the main lobes -3db mark. Regards Michael Baird > I'd argue none of the 3 above. > > For 900Mhz and 2.4Ghz (because of wider Verticle beamwidths) I'd advise.... > Downtilt until your mainlobe (3db mark) edge is no longer going beyond your > maximum intended coverage range, or a bit more, if you can afford further > isolation from the potential adjacent cell interference source. > > The primary goal is to keep harmfull interference from shooting off to the > horizon (ultimately protecting your network since receive gain/beamwidth is > reciprocal). How much tilt is required to do that, depends on the antenna > beamwidth, and the height that you decide to install at, for what ever > reason. > > In 5.8G its less critical because you can make up for it on CPE side antenna > side, and ther eare much fewer noise sources at 5.8Ghz. > That is until your 5.8G area gets congested :-( But because 5.8G may have > smaller verticle beamwidths, the nearfield potentially could be more of a > concern, that the other freqs. > > Tom DeReggi > RapidDSL & Wireless, Inc > IntAirNet- Fixed Wireless Broadband > > > ----- Original Message ----- > From: "Michael Baird" <m...@tc3net.com> > To: "WISPA General List" <wireless@wispa.org> > Sent: Tuesday, March 10, 2009 8:53 AM > Subject: Re: [WISPA] 900 Downtilt at 300' > > > >> 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/ >> >> >> -- >> 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/
