I know empirically the big wind turbine blades affect 5 GHz PMP links in cases where I could think they are well outside first Fresnel zone. It can be pretty dramatic listening to the Cambium alignment tone (we typically use a little amplified speaker so even the person on the ground can hear it).
Maybe because the 1st, 2nd, 3rd, etc. Fresnel zones still contribute to the received signal (either adding or subtracting), it’s just a rule of thumb that if you have 0.6 or 1.0 Fresnel clearance you’re good to go. But if they have a complex analysis method that’s probably best. I don’t know how fast the AGC is on a licensed radio, but the turbine blades turn pretty slow. Whoosh … whoosh … whoosh. From: AF <[email protected]> On Behalf Of Eric Nielsen Sent: Friday, February 28, 2020 7:00 PM To: AnimalFarm Microwave Users Group <[email protected]> Subject: Re: [AFMUG] freznel impact calculator Yeah, the process is completely outside of the standard interference analysis database. I don’t recall the tools they use, but it performs a 3D analysis and calculates the fresnel clearances when plotting the turbines, factoring the hub height and blade length. Pretty cool stuff. On Fri, Feb 28, 2020 at 5:56 PM Steve Jones <[email protected] <mailto:[email protected]> > wrote: Im reaching out to them, they did a path study for a similar thing on one of our links, it was not on our dime for that link, so maybe we didnt get a full dataset and report back, we just got a yes/no on impact, but not enough detail to make a risk assessment. They told me they have access to the turbine database outside the normal link analysis. On Fri, Feb 28, 2020 at 6:47 PM Eric Nielsen <[email protected] <mailto:[email protected]> > wrote: Comsearch does something called a “reverse geoplanner”. If you provide them with the turbine locations and the path details they’ll tell you the risk of fresnel obstruction. They’re equipped to do this because they perform the microwave studies for wind farms. On Fri, Feb 28, 2020 at 5:43 PM Steve Jones <[email protected] <mailto:[email protected]> > wrote: I have a 3 link path i need to turn up in 11ghz. we drove the path yesterday. 2 legs are golden. one however is problematic, ive got two wind turbines that are in or just outside the fresnel. If it were one, id probably be inclined to risk the impact if there was just one turbine, but two is iffy without some good maths to support it. The path is 5.5 miles the first turbine is 3.64 mile the second is about 4.69 miles Fresnel is about 25' radius at that distance max if the calculator is right the first turbine is maybe 100' from boresite the second is probably 150' These arent our normal turbines, these the the bad motherfucker turbines, so the blades are like a million feet long, actually IIRC theyre 224' on something like a 400' pedestal. I need to pull the specs again on those and get better than google earth GPS coordinates on the potential end points, and some better actual heights that brings be to the question, how do i calculate a partial fresnel obstruction with a radius like the blade pattern. I figure boresite view with a 50' circle would give me worst case fresnel, then i just draw the arc of the turbine path into that as an obtruction for each maybe just shade the polygon it create as a complete obstruction. So once i have that info, what tool can i put it into to calculate the impact? everything we use just has an obstruction height. Would i be able to just take the distance from edge of fresnel into the furthest point of the polygon? Would I need to calculate more loss than that? Im planning on sticking a 5ghz link up anyway pending licensing, so i assume i can just extrapolate the loss from that -- AF mailing list [email protected] <mailto:[email protected]> http://af.afmug.com/mailman/listinfo/af_af.afmug.com -- Eric Nielsen 571-508-7409 [email protected] <mailto:[email protected]> -- AF mailing list [email protected] <mailto:[email protected]> http://af.afmug.com/mailman/listinfo/af_af.afmug.com -- AF mailing list [email protected] <mailto:[email protected]> http://af.afmug.com/mailman/listinfo/af_af.afmug.com -- Eric Nielsen 571-508-7409 [email protected] <mailto:[email protected]>
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