I wonder if the FCC would be open to a discussion about allowing higher TX power on SM's considering that that are usually way lower to the ground then AP's tend to be mounted.
On Thu, Nov 21, 2019 at 1:06 PM Adam Moffett <dmmoff...@gmail.com> wrote: > Only AP > On 11/21/2019 1:04 PM, Kurt Fankhauser wrote: > > 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 <af...@kwisp.com> 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 <af-boun...@af.afmug.com> *On Behalf Of *Adam Moffett >> *Sent:* Thursday, November 21, 2019 11:27 AM >> *To:* af@af.afmug.com >> *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 <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 >> 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 >> > > -- > AF mailing list > AF@af.afmug.com > http://af.afmug.com/mailman/listinfo/af_af.afmug.com >
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