That was the band of the radar I visited. Sent from my iPhone
> On Nov 21, 2019, at 12:17 PM, Ken Hohhof <[email protected]> wrote: > > > That’s pretty cool. The links to ULS are nice. > > I had always wondered whose radar that was by Routes 47 and 64 your map tells > me it’s WLS-TV. So if ULS says the frequency is 2900-2950, that means the > actual radar beam is in that range? Not in 5 GHz at all? > > > From: AF <[email protected]> On Behalf Of Mike Hammett > Sent: Thursday, November 21, 2019 1:05 PM > To: AnimalFarm Microwave Users Group <[email protected]> > Subject: Re: [AFMUG] dumb DFS questions > > This is nowhere near complete, but here is a map I've been building of radar > sites. > > https://drive.google.com/open?id=1ayAnN9KSq09zKS8WCqaQ_QA3JrY&usp=sharing > > It has TDWR, NOAA, TV stations etc. The private radar stations (mostly TV > stations) are the incomplete part of the map because I have to look them up > in ULS. It is complete in our area. > > > > ----- > Mike Hammett > Intelligent Computing Solutions > > Midwest Internet Exchange > > The Brothers WISP > > > > From: "Ken Hohhof" <[email protected]> > To: "AnimalFarm Microwave Users Group" <[email protected]> > Sent: Thursday, November 21, 2019 12:36:28 PM > Subject: Re: [AFMUG] dumb DFS questions > > Chicago has 2 TDWRs (for OHare and Midway) and both are in the 5600-5650 MHz > band. I think a lot of WISP equipment actually locks out those frequencies, > and the only place a WISP would be desperate enough to use that 50 MHz > apparently is Puerto Rico, which is apparently the Wild West of spectrum. > > http://www.wispa.org/Resources/Industry-Resources/TDWR-Resources/TDWR-Locations-and-Frequencies > > > > From: AF <[email protected]> On Behalf Of [email protected] > Sent: Thursday, November 21, 2019 12:16 PM > To: 'AnimalFarm Microwave Users Group' <[email protected]> > Subject: Re: [AFMUG] dumb DFS questions > > Those radars sweep the sky pretty slowly. Like 60 rpm. It would be > theoretically possible to be on their frequency and just blank TX when it is > looking your way. You could extract timing sync from the radar sweep and > figure out when to blank. Their gain is such that you would only have to > blank for perhaps 50 mS. > > If I had more ambition I would ask for an experimental license to play with > the idea. > > From: Ken Hohhof > Sent: Thursday, November 21, 2019 11:11 AM > To: 'AnimalFarm Microwave Users Group' > Subject: Re: [AFMUG] dumb DFS questions > > Only the APs, at least under FCC rules, I’m not sure about the rest of the > world. > > That alone IMHO says DFS is a joke, or regulatory “experts” deluding > themselves. If I have a sector pointed away from some government radar, it > won’t detect the radar, but the SMs are pointed back at the radar and are not > required to have a detection mechanism. Probably a good point that it would > be too complicated for one SM to detect radar and then communicate with the > AP to request a channel change. But you really need something like a SAS for > this spectrum sharing idea to work. > > > From: AF <[email protected]> On Behalf Of Kurt Fankhauser > Sent: Thursday, November 21, 2019 12:04 PM > To: AnimalFarm Microwave Users Group <[email protected]> > Subject: Re: [AFMUG] dumb DFS questions > > one thing i have always wondered is do the SM's actually look for RADAR or > only the AP's? > > On Thu, Nov 21, 2019 at 12:55 PM Ken Hohhof <[email protected]> wrote: > Yes, that’s true, but a higher gain antenna at the SM end helps rcv but not > xmt. And SMàAP is the direction you may actually need a better signal > because the AP likely has a sector antenna and is mounted higher so it sees > more interference. > > It would not be unusual to have a 16 dBi antenna at the AP but a 25 dBi > antenna at the SM. The antenna gain would help the rcv signal at the SM, but > it would probably have to lower its conducted power by 9 dB to stay within > the regulatory EIRP limit. > > In contrast, in U-NII-3 the CPE end is treated as point-to-point and can use > antenna gain to exceed the AP limit of 36 dBm EIRP (subject to OOBE limits). > > From: AF <[email protected]> On Behalf Of Adam Moffett > Sent: Thursday, November 21, 2019 11:27 AM > To: [email protected] > Subject: Re: [AFMUG] dumb DFS questions > > 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 <[email protected]> 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 > [email protected] > http://af.afmug.com/mailman/listinfo/af_af.afmug.com > > > -- > AF mailing list > [email protected] > http://af.afmug.com/mailman/listinfo/af_af.afmug.com > -- > AF mailing list > [email protected] > http://af.afmug.com/mailman/listinfo/af_af.afmug.com > > -- > AF mailing list > [email protected] > http://af.afmug.com/mailman/listinfo/af_af.afmug.com > > -- > AF mailing list > [email protected] > http://af.afmug.com/mailman/listinfo/af_af.afmug.com
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