Please do not down grade all engineers. Some of us with degrees realize that the real world is not the lab world. Over 45 years has shown me that very few antenna installations are the same. I have seen deep nulls on single antenna installations on large surface towers. One I remember well, you could see the antenna at 6.5 miles, but could not key the repeater with a 100 watt mobile on high band but had very good coverage at 45 miles out. Water towers and tall buildings seem to be the worst case for 450 and 800 MHz, multiple reflections from other antennas and flat surfaces, to many to calculate. As you stated "Every site has to be evaluated on its merit." and it takes some common sense to see the radio horizon and gain isn't everything! Fred W5VAY ----- Original Message ----- From: "Paul Finch" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Tuesday, March 08, 2005 8:40 PM Subject: RE: [Repeater-Builder] Inside a Flag pole Tower
> > Sometimes the system has not read the physics book! I once worked with four > PHD's, 3 out of four said I would never make a circuit work, one abstained. > I did make it work, and it worked better than the one the PHD's came up > with! They were scratching there heads! By the way, I never darkened the > door of any college. > > Maybe I was to stupid to know it would not work because my engineering > skills were self taught and OJT, none of it in the classroom. That's how a > lot of advances in today's technology based world happens, and not always > from a College educated engineer. > > All I was saying in my original post was that you can't arbitrarily say > "never" use more than a 8 dB antenna at 100 feet. Every site has to be > evaluated on it's own merit and I stand by that statement! > > Paul > > > -----Original Message----- > From: Kevin Custer [mailto:[EMAIL PROTECTED] > Sent: Tuesday, March 08, 2005 7:15 PM > To: [email protected] > Subject: Re: [Repeater-Builder] Inside a Flag pole Tower > > > > Joe Montierth wrote: > > >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 > > > > > > Same stuff happens out here in the east. I have had the exact same > experience as suggested in the text above. > > Kevin Custer > > > > > > > Yahoo! Groups Links > > > > > > > > > > > > > > > > Yahoo! Groups Links > > > > > > > > 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/
