Well, before he invests in an install, have him rent a lift truck or something to see what he can see.
I have a few links that have this type of knife edge defraction. I run them using 802.11 gear (Mtik/Tranzeo). When I allowed full on access to all the speed I could provide, complaints came from these clients. When I throttled them down to256/768/1M connections.. the complaints stopped and things were more normalized to these clients. ryan On Tue, Feb 23, 2010 at 7:05 AM, Mike <[email protected]> wrote: > I have a bright beacon I can turn on at the top of this tower. On a clear > night recently, I turned it on. Even a ways up a corn crib he could NOT > see > the light. I think the terrain data is accurate. The alphimax site, once > you create the path lets you go into Google Earth and "see" the hill. This > part of the world doesn't have high resolution imagery archived yet, but I > CAN see the ridge when I follow along the path. > > -----Original Message----- > From: [email protected] [mailto:[email protected]] On > Behalf Of Josh Luthman > Sent: Tuesday, February 23, 2010 9:01 AM > To: WISPA General List > Subject: Re: [WISPA] That black magic > > To begin with, are you sure there is a bump there? Could it be bad > meter resolution? > > Josh Luthman > Office: 937-552-2340 > Direct: 937-552-2343 > 1100 Wayne St > Suite 1337 > Troy, OH 45373 > > “Success is not final, failure is not fatal: it is the courage to > continue that counts.” > --- Winston Churchill > > > > On Tue, Feb 23, 2010 at 9:55 AM, Mike <[email protected]> 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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