Dean specified 100ft AAT, which takes into account the ground elevation, thats not very high off the ground.
I own a 140 ft tower, with antennas that have relatively high gains. I can sit at the bottom of the tower (which should be the worst null) and still hear and get into the repeater. I can move .5 mile away with the same results. I can move 3 or 5 miles away with the same results. The null zones created by high gain antennas are usually so close to the antenna (when at 100 ft) that it makes no difference. By the time you get into the major lobe of the antenna, you will less than a mile or so away from the tower; as you get further away, you just get more and more into the beamwidth, not less. A high gain antenna may have a pattern that is 8 degrees, that would be 4 degrees above the horizon, and 4 degrees below the horizon. With an antenna 100 ft AAT, you would come into the major lobe just a little over a quarter mile from the antenna. I think most people would agree that if you're closer than .25 miles to an antenna at 100 ft, you won't have a lot of problem hearing (or getting into) the attached repeater. I too, have worked in the RF field for a long time, and seen some strange stuff. One thing I consistantly see is that a high gain antenna will almost always outperform a lower gain antenna at the fringes, or near the horizon. It doesn't seem to matter if it is a 100 ft tower, or a ten thousand foot mountain. Even on the 10,000 ft mountain it is hard to make the "nulls" of much consequence, since they are such an angle, reference the major lobe. This is from real-world experience also. Pehaps the laws of physics and trigonometry are different out east, I am only relying on "wild west" observations. :) Joe --- [EMAIL PROTECTED] wrote: > > I'm sorry Joe but Dean is correct. I believe you > might be forgetting about > the angle of radiation off the antenna and the null > zones it creates. > Higher gains create larger near field null zones so > you have to pick a gain > that gives good coverage but won't exclude mobiles > that are near the site. > > The other factor that you have to take into > consideration is the elevation > that the flag pole is going to be erected at. Now > add to that the flag > poles are smaller in foot print diameter than normal > cell phone towers which > places the antennas inside them in closer proximity > to each other and you > have to minimize interaction with each other. Using > high gain antenna's > causes more problems with interaction so you have to > reach a happy medium. > > Sorry to say Trig is one thing but real world RF is > another. I have worked > in the RF field almost as long as Dean and have seen > many strange things > happen. > > Mike > K1EG > ----- Original Message ----- > From: "Joe Montierth" <[EMAIL PROTECTED]> > To: <[email protected]> > Sent: Tuesday, March 08, 2005 10:22 AM > Subject: Re: [Repeater-Builder] Inside a Flag pole > Tower > > > > > > > > --- [EMAIL PROTECTED] wrote: > > > 1st off that was not a put down! > > > I will not blow my on horn but > > > I can say if it works for you then > > > use it. BUT! It is not how antenna > > > physics work. Just think how much > > > better a system will work when we do > > > not try to change the laws and rules > > > of antenna physics? > > > Dean Westbrook, EE,PE > > > > > > > Then don't try to change the laws of trigonometry > > either. > > > > 100ft tower, 40 miles out, what's the angle? For > that > > matter, figure at 5 and ten miles also. > > > > At those short antenna heights you will usually > want > > the maximum gain, unless your prime coverage is in > the > > first half mile or so. > > > > Joe > > > > __________________________________________________ > > Do You Yahoo!? > > Tired of spam? Yahoo! Mail has the best spam > protection around > > http://mail.yahoo.com > > > > > > > > > > > > Yahoo! Groups Links > > > > > > > > > > > > > > > > > > > > > > > > > Yahoo! Groups Links > > > [EMAIL PROTECTED] > > > > > > __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
