We see some of the same interference issues. It was actually much better when all the cordless phones were 900, verses meters, farm operations, etc...
Yes it's NLOS, if I went up another 40 ft I would have LOS. With NLOS we only have about 25 yards of trees to deal with 100 yards or so from the house, but no dirt. He's 1.35 miles from the tower, the AP is 150 above his GL. We do use a Cushcraft 906 antenna on his end and an Antel 120 deg, 3 deg electrical down tilt on the tower that puts out 34.8 EIRP. A filter we changed out a couple of years ago dropped our output a bit more than a db. Now that the beans are gone, his signal stabilized and improved from a fluctuating -75 to -83 back to a -70 This is an older CCU3100 WaveRider system that doesn't run OFDM, but DSSS. I tried a panel antenna instead of the yagi and it improved the fluctuation some, but didn't improve the signal like going up 10 ft did. So I think you are correct that the changes in multipath from a little wind and lots of hardened leafs and beans reflected the signal more than when they had enough moisture to absorb more than reflect. Dave Mike wrote: > 900 MHz doesn't work well around here. The farmers have deployed GPS > navigation systems using those frequencies. > > Was the bean path you had NLOS? I'm curious what effects it had. I have > seen a four foot change in elevation work like black magic. I think the > beans get to blowing in the breeze and because there are hundreds of > thousands of little hard points that randomly diffract the signal it fades. > I saw this on a knife edge diffraction path as well as a distant, path where > the CPE had to be mounted low to clear large branches of an oak tree 20 feet > overhead. The next field over was a bean field one year and caused fits for > a couple weeks, I believe because of the low angle. Is it that OFDM can > survive in a multipath environment until the individually randomized signals > number in the thousands? > > Mike > > -----Original Message----- > From: [email protected] [mailto:[email protected]] On > Behalf Of David Hulsebus > Sent: Tuesday, February 23, 2010 3:04 PM > To: WISPA General List > Subject: Re: [WISPA] That black magic > > Mike, Interesting you mentioned soy beans. I have a customer > (900-WaveRider) who was installed for 5 yrs next to a corn field. The > crop was replaced with soy beans this past year and a month before > harvest, as the beans dried out, we started having signal fluctuation > issues. We raised the antenna 10 ft and the problem went away. It was > their first issue in 5 yrs. > > Dave > > > > Mike wrote: > >> I need to do a reality check with those of you familiar with knife edge >> diffraction as a propagation medium. First, I should paint the scene: >> >> >> >> I have a corporate farmer almost 16 miles away who is motivated. His >> options are satellite, dialup he currently uses, or us. >> >> >> >> A spectrum sweep of the property found absolutely no 2.4 signals. By in >> large, these rural areas are very quiet. >> >> >> >> There are no trees or obstructions in the near field or out quite a ways. >> However, there is a ridge almost half way between us. I am embedding an >> image of the path here created with alphimax.com path estimator. >> >> >> >> >> >> >> >> >> >> I have a test unit which is a 19 dB panel/radio with an AP fastened to the >> back. It lets me hand hold a test unit and see what it sees on a laptop. >> Standing on the ground on his property we got an ALMOST usable signal in a >> short test. He has a 35 foot TV tower next to the house on which we would >> install. >> >> >> >> Perhaps one would look at the path profile and common sense would dictate >> > it > >> won't work. However, I use knife edge diffraction successfully on a >> > handful > >> of installs. Besides, black magic sometimes trumps common sense. >> >> >> >> I have never used this technique where the ridge is close to mid point. >> > On > >> all others the ridge was closer to the user. All of them work except when >> tropospheric ducting enters into the equation, with one exception. I have >> told the users this is a 98% link and it WILL go down during those events. >> Earlier this winter we had a few days of ducting which caused a couple of >> them to fade. I saw a 15 dB fade on those. Statistically, ducting should >> only affect this area 20 some hours a year. >> >> >> >> The single exception was when the obstructing hill had soy beans growing >> > on > >> it. That particular one went down in late fall when the beans were ready >> for harvest. The previous 2 years the field had corn planted on it and >> > had > >> absolutely no issues. I think dry beans affect the signal because they >> > are > >> no longer "row" polarized and randomly scramble the signal beyond use. >> > Once > >> the beans were harvested, the signal came back like usual. >> >> >> >> On this path in question, I found the ridge. There are no trees, instead >> > it > >> is farmed. There is corn stubble on it right now. >> >> >> >> I am curious what others have found in these NLOS situations. Because the >> obstruction is mid path, will the signal still be there next fall as it is >> now? Are mid path obstructions on a long path better than obstructions >> closer to one end? Am I absolutely stupid for even considering this >> install? >> >> >> >> I went over all the physics involved and told him of my experiences. Like >> > I > >> said, he is motivated. I told him I wouldn't tie him into a contract, but >> we'd go month by month and if we found later in the year it wasn't >> > working, > >> we'd cut our losses. He was OK with that. >> >> >> >> Since I respect the viewpoints of many of you, bring it on! >> >> >> >> >> >> Friendly Regards, >> >> >> >> Mike >> >> >> >> Mike Gilchrist >> >> Disruptive Technologist >> >> Advanced Wireless Express >> >> P.O. Box 255 >> >> Toledo, IA 52342 >> >> Mike's >> >> > <http://www.tamatoledonews.com/page/category.detail/nav/5001/Local-Columns.h > >> tml> Weekly Column >> >> 239.770.6203 >> >> [email protected] >> >> >> >> >> >> >> >> ------------------------------------------------------------------------ >> >> >> >> >> > ---------------------------------------------------------------------------- > ---- > >> WISPA Wants You! 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