They all work because antennas do NOT just stop radiating in a given direction. They actually send energy all over the place, it's just stronger in one direction than in the others.
We often talk about antennas like a flashlight, but that's not really quite accurate. It's more like a light bulb with a sheet of paper behind it. You'll not see as much light, depending on the type of paper, but you'll still see some. Same thing goes for the sides.... marlon ----- Original Message ----- From: "Michael Baird" <m...@tc3net.com> To: "WISPA General List" <wireless@wispa.org> Sent: Tuesday, March 10, 2009 5:53 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! 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