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
<mailto: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
<mailto:af-boun...@af.afmug.com>> *On Behalf Of *Adam Moffett
*Sent:* Thursday, November 21, 2019 11:27 AM
*To:* af@af.afmug.com <mailto: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 <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?
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