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 >
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