Yes, Military radar is the primary reason for DFS complexities.
----- Mike Hammett Intelligent Computing Solutions Midwest Internet Exchange The Brothers WISP ----- Original Message ----- From: "Robert Andrews" <i...@avantwireless.com> To: af@af.afmug.com Sent: Thursday, November 21, 2019 2:30:05 PM Subject: Re: [AFMUG] dumb DFS questions I thought Military aircraft radars could also use DFS frequencies? On 11/21/2019 09:50 AM, Kurt Fankhauser wrote: > We are using DFS on PMP450 for customer access and AF5XHD for backhauls. > It works surprisingly well. On both the PMP450 and AF5XHD's you can set > an alternative freq and a secondary alternative for the radios to > immediately jump to if they detect RADAR. Radios will try the first alt > freq and if they get a hit on that will then go to the second freq. It > should happen instantly without taking the link down. If you do not set > the alt freqs the radios will shutdown for 30 minutes and then > attempt to use that freq again. I have noticed that the wider the > channels you use the more "susceptible" you are yo getting a radar > event. Try running on 20mhz channels and you wont get as many hits if > any. We have some AP's that have been running for 6 months+ without any > radar hits. We are also not anywhere near any airports so that may be > helping us as well. > > On Thu, Nov 21, 2019 at 12:42 PM Matt Hoppes > <mattli...@rivervalleyinternet.net > <mailto:mattli...@rivervalleyinternet.net>> wrote: > > You do. > > On 11/21/19 12:27 PM, Adam Moffett wrote: > > There might be something I don't understand, but I thought you > had flat > > EIRP limit of +30dbm whether it's an SM or an AP. > > > > On 11/21/2019 12:11 PM, castarritt . wrote: > >> 6 dBm loss for the AP transmit isn't the end of the world. It's > the up > >> to 23 dBm loss on the SM transmit power that destroys the > >> usefulness of DFS for PTMP past a couple miles. The ~16 dBi gain > 90° > >> sectors 2-300' up in the air just can't hear those SMs over all the > >> noise they are picking up. What we need is the ability to run > >> downlink on DFS and uplink on 5.2 or 5.8. > >> > >> > >> On Thu, Nov 21, 2019 at 10:56 AM Adam Moffett > <dmmoff...@gmail.com <mailto:dmmoff...@gmail.com> > >> <mailto:dmmoff...@gmail.com <mailto:dmmoff...@gmail.com>>> wrote: > >> > >> Yeah I think on most equipment you can set alternate > channels that > >> are just shifted over 5mhz from where you were. And yeah I > think > >> the channel needs to be clear for a few minutes before you > can go > >> back to it. > >> > >> Assuming you don't really have a TDWR near you, I don't > think DFS > >> events are that big of a deal. My understanding is that DFS > >> events are more likely if you lie to the software about antenna > >> gain to cheat the EIRP limit. False detects happen, but I don't > >> think it's a daily event. Disclaimer: I've mostly used it on > >> Point to point with dishes. I'm not sure if you'd pick up more > >> anomolies on a sector antenna. > >> > >> The biggest bummer is the EIRP limit. When you're trying to get > >> that 32 SNR for the 256QAM then losing 6db kind of hurts. > Or when > >> you've already got someone hooked up 10 miles away and lowering > >> the power ruins them. > >> > >> Where you really want to use DFS (In my opinion) is at a site > >> where you have a bunch of customers within 1-2 miles. > >> Unfortunately I don't have sites like that. > >> > >> -Adam > >> > >> > >> > >> On 11/21/2019 11:31 AM, Ken Hohhof wrote: > >>> > >>> We mostly avoid DFS frequencies on APs because of the impact if > >>> we get false radar detects. Also we are mostly a Cambium > shop. > >>> So I’m a bit confused about DFS on other vendor equipment like > >>> Ubiquiti as well as home routers. > >>> > >>> Question 1 – what happens when there’s a DFS detection? On the > >>> Cambium gear, we have to select 1 or 2 alternate frequencies. > >>> But on other gear, I don’t see this. When there’s a DFS hit, > >>> does it jump to another random frequency? Does it rescan the > >>> current frequency until it tests clear and only then resume > >>> transmission? Is the answer right in front of me and I’m being > >>> stupid? Maybe in the case of routers they are exempt > because of > >>> low EIRP? > >>> > >>> Question 2 – what about 40/80/160 MHz channels? We have a > >>> competitor using Ubiquiti gear and advertising residential > >>> subscriber speed plans up to 100x100. Clearly they must be > using > >>> at least 40 MHz channels if not 80 MHz, or else their marketing > >>> people have burning pants and long noses. And I don’t see how a > >>> WISP, especially one surrounded by other WISPs, could use wide > >>> channels other than in DFS bands. We have some PTP links using > >>> 40 MHz but only 10 and 20 MHz channels on our APs. So assuming > >>> you are using 40 or 80 MHz in DFS, what happens when there’s a > >>> DFS detect? Does the whole 40 or 80 MHz have to find a new > >>> home? Can it slide over 2.5 or 5 MHz and substantially overlap > >>> the previous occupied spectrum? DFS bands come with enough > >>> spectrum to use wide channels, but is there enough to jump > around > >>> when you take a DFS hit? > >>> > >>> > >> -- > >> AF mailing list > >> AF@af.afmug.com <mailto:AF@af.afmug.com> <mailto:AF@af.afmug.com > <mailto:AF@af.afmug.com>> > >> http://af.afmug.com/mailman/listinfo/af_af.afmug.com > >> > >> > > > > -- > AF mailing list > AF@af.afmug.com <mailto:AF@af.afmug.com> > http://af.afmug.com/mailman/listinfo/af_af.afmug.com > > > -- AF mailing list AF@af.afmug.com http://af.afmug.com/mailman/listinfo/af_af.afmug.com
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