Keeping in mind that stuff on the Internet is not always true, quoting Wikipedia:
“NLOS links may either be simplex (transmission is in one direction only), duplex (transmission is in both directions simultaneously) or half-duplex (transmission is possible in both directions but not simultaneously). Under normal conditions, all radio links, including NLOSl are reciprocal—which means that the effects of the propagation conditions on the radio channel are identical whether it operates in simplex, duplex, or half-duplex.[5] Please remember that propagation conditions on different frequencies are different, so traditional duplex with different uplink and downlink frequencies is not necessarily reciprocal.” https://en.wikipedia.org/wiki/Non-line-of-sight_propagation#What_is_line-of-sight.3F This assumes passive, linear devices. Exceptions would include amplifiers, circulators/isolators/duplexers, ferrite based antennas, etc. But as far as the RF path itself including microwave antennas, I’ve never seen asymmetry. If the path loss is different in the two directions, my admittedly limited experience has always been it’s due to the electronics. This might not hold with modern NxN MIMO radios where the signals are extensively processed, with different processing in the uplink and downlink directions. The RF path might indeed by symmetric, but the effect on the 2 directions could be different. BTW, I see the citation in the Wikipedia article is Ramo, Whinnery and Van Duzer which sounds familiar, meaning it must have been one of my college texts from a dreaded “Fields and Waves” course. So it is a very, very old book. I’ll have to check my bookshelf at home to see if I’ve got it. Much of microwave theory was developed 50 years ago, so it’s not necessarily wrong just because it’s old. Amazing what people used to design with slide rules. From: Glen Waldrop Sent: Thursday, August 27, 2015 8:44 AM To: af@afmug.com Subject: Re: [AFMUG] Spacial Diversity - helps how much? I would think with reflections and defraction they might not be symetric. Running that through my head right now... If the shape of the obstacle is just right to cause a bend from east to west and have it bend to line up with the west side RX, but the angle different on the opposite side, so it causes west to east to reflect. Not quite half way through my first cup of coffee, so if that didn't make sense, I blame Folgers. ----- Original Message ----- From: Ken Hohhof To: af@afmug.com Sent: Thursday, August 27, 2015 8:31 AM Subject: Re: [AFMUG] Spacial Diversity - helps how much? Usually RF paths are symmetric, if it helps xmt I would expect it to help rcv. From: Mike Hammett Sent: Thursday, August 27, 2015 8:26 AM To: af@afmug.com Subject: Re: [AFMUG] Spacial Diversity - helps how much? Where you have multiple antennas, I believe it only helps on those antennas receiving. ----- Mike Hammett Intelligent Computing Solutions http://www.ics-il.com ------------------------------------------------------------------------------ From: "Adam Moffett" <dmmoff...@gmail.com> To: af@afmug.com Sent: Thursday, August 27, 2015 8:14:01 AM Subject: Re: [AFMUG] Spacial Diversity - helps how much? Ok, here's another dumb question: If I only have spatial diversity on the tower side and not on the client side, does that actually help both directions, or only the uplink? I was told in the past that it only helps on the uplink. On 8/26/2015 9:16 PM, David Milholen wrote: Spatial Diversity is mainly used to over come multipath issues or a link that will stretch the curvature of the earth. It is really interesting what link planner does when you configure for spatial diversity on a link. There are a ton of factors that go into getting reliability,throughput or both. The longest link I ever did was 71mile using 4x 4ft HP dishes on either end of the link with ptp600 radios. We had connection and enough reliable bandwidth to do what we needed. I dont think I ever saw much loss with rain fade either. That is what sold me on the product. When the link was configured it had to have the H and the V swapped at opposite ends of the length and the spatial distance was slightly different at each end On 8/26/2015 12:03 PM, Rory Conaway wrote: Part of the idea between spatial diversity is creating a second path that won't have the same obstructions. Take this out of the idea of the MIMO technology and simply go with the idea that possibly one path will have different or less tree blockage/absorption or possibly that reflections are more advantageous than a single path. I did this in an RV park but didn’t have anything to compare it to so did it work better, I'm not sure. Rory -----Original Message----- From: Af [mailto:af-boun...@afmug.com] On Behalf Of Adam Moffett Sent: Wednesday, August 26, 2015 8:20 AM To: af@afmug.com Subject: [AFMUG] Spacial Diversity - helps how much? There are a couple of products out there selling 4x4 MIMO (Telrad is one, but there are others). In Telrad's case, two of the chains have a time offset from the other two, so you get two chains on each of two polarities. Their default antenna is a single sector antenna with 4 N-connectors on it, so there's no significant spacial diversity. In the past it's been suggested that we use two dual pol sector antennas and space them 3 feet apart to get spacial diversity. When I asked why they do the single antenna, a source at Telrad told me that spacial diversity "only helps a little". The party selling us the two panels considers it to add 6db when they run coverage projections. I suspect any gain from spacial diversity is going to depend on a lot of circumstances and I doubt it could be as simple as adding 6db. I'm wondering if anyone here has any opinions on the topic? Maybe even facts :) (I'm sort of eyeballing a certain guy in Utah who designs antennas and isn't trying to sell me anything.) --
