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" <m...@aweiowa.com> To: "'WISPA General List'" <wireless@wispa.org> 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 > > m...@aweiowa.com > > > > > > -------------------------------------------------------------------------------- > > > -------------------------------------------------------------------------------- > WISPA Wants You! Join today! > http://signup.wispa.org/ > -------------------------------------------------------------------------------- > > WISPA Wireless List: wireless@wispa.org > > Subscribe/Unsubscribe: > http://lists.wispa.org/mailman/listinfo/wireless > > Archives: http://lists.wispa.org/pipermail/wireless/ -------------------------------------------------------------------------------- WISPA Wants You! Join today! http://signup.wispa.org/ -------------------------------------------------------------------------------- WISPA Wireless List: wireless@wispa.org Subscribe/Unsubscribe: http://lists.wispa.org/mailman/listinfo/wireless Archives: http://lists.wispa.org/pipermail/wireless/
