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