I wondered if you'd weigh in. I will use a grid at this location. I think my grids are 22 dB. What 24 dB ones are you using?
I had a LOS once where the ONLY thing in the way was a power line. It dropped lots of packets until I lowered it a bit and put a little down tilt to the panel. The "unseen" energy around that wire must have been enough to obstruct too much of the Fresnel zone. I appreciate all of the input. It's still been too cold and windy to send him up his Rohn 25 to see if he can indeed see the light. That will be my next step. Mike -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Marlon K. Schafer Sent: Tuesday, February 23, 2010 10:18 PM To: WISPA General List Subject: Re: [WISPA] That black magic First off, with a LEGAL base station AP running 36dB (I used 24db radio with 12dB sector as an example) you should see a -73 at 16 miles. Personally, to help avoid interference, I use 30dB or so ap power and run 24dB grids at anything past 8 miles. Things run pretty well this way. Multipath is a really hard thing to figure out some times. Had one today, high tension power lines about half way. Good signals but 80 to 90% retrans rates. I finally found a channel that worked well and got 3 megs both ways to the customer, but everything else I tried only gave me half a meg down and less up most of the time. I gave the customer a 2 week trial before they have to pay for the install. We'll see if it keeps running or not. I don't have high hopes. I'll try moving the antenna up or down before I pull it out and see if I can find a better spot. In the end, some just never do work right. marlon ----- Original Message ----- From: "Mike" <[email protected]> To: "'WISPA General List'" <[email protected]> Sent: Tuesday, February 23, 2010 6:55 AM Subject: [WISPA] That black magic >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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