Date: Mon, 5 Apr 2021 08:29:30 -0500 From: Valeri Galtsev <galtsev@kicp.uchicago.edu> To: Peter Cornelius <pcc@gmx.net> Cc: freebsd-questions@freebsd.org Subject: Re: Wifi scanner for FreeBSD Message-ID: <91D8B6CF-753A-4A10-A505-1673059EDB64@kicp.uchicago.edu> In-Reply-To: <trinity-bc777486-adab-486e-b7c6-dbafa025bab8-1617606747224@3c-app-gmx-bs57> References: <YGl3fCIhTnbowOVi@c720-r368166.fritz.box> <20210404185713.4d19ea73@ws1.wobblyboot.net> <YGmEVK8zs7caSFon@c720-r368166.fritz.box> <YGmO73%2BMLWl3wyD1@mithril.foucry.net> <20210404204512.3ba04756@ws1.wobblyboot.net> <20210404133536.4fedf1e0@archlinux> <trinity-bc777486-adab-486e-b7c6-dbafa025bab8-1617606747224@3c-app-gmx-bs57>
next in thread | previous in thread | raw e-mail | index | archive | help
> On Apr 5, 2021, at 2:12 AM, Peter Cornelius <pcc@gmx.net> wrote: >=20 > G'day, folks, > =20 > Regarding the first post, I would not mind to see such application in = ports myself though I think that the mobile apps suggest more than they = hold. > =20 > Regarding 2.4 GHz WiFi, I have come to the conclusion that I will = avoid that band with WiFi wherever I can. I have the experience from my = earlier place in town where I was able to see the beacons of the order = of 50 wlans, that a single station not on one of the non-overlapping = bands [1] causes so much interference to all on one of the = non-overlapping ones that there is no throughput at all for anyone. I = don't know what kind of pot people had when they invented that standard, = but that's how it is.=20 There is one more rationale to avoid 2.4 GHz band: there are commodity = devices that create strong interference in this band: microwave ovens, = cordless phones. However, if you are in the building with =E2=80=9Cwet=E2=80=9D wall (any = construction material that may host water: most notably brick, = concrete), then 5 GHz will work on much closer range than 2.4 GHz: = higher rf frequencies are more efficiently absorbed by construction = materials. I hope, this helps. Valeri > When you use such 'free' channel (as in the image at the mail starting = this thread), all that happens is that you can't decode the others, and = the others can't decode your emissions but you very effectively = interfere with each other, making the entire spectrum unusable. And all = the blue teeth and other emissions on that band just add to that. > =20 > In short, if all stick to the non-overlapping channels (and do not = bundle), one may get some throughput as the protocol can control the = channel. If one deviates, forget it. > =20 > Just my 2 cents. > =20 > Cheers, > =20 > Peter. > =20 > [1] https://en.wikipedia.org/wiki/List_of_WLAN_channels > =20 >=20 >=20 > =20 >=20 > Gesendet: Sonntag, 04. April 2021 um 13:35 Uhr > Von: "Ralf Mardorf" <ralf-mardorf@riseup.net> > An: freebsd-questions@freebsd.org > Betreff: Re: Wifi scanner for FreeBSD > On Sun, 4 Apr 2021 20:45:12 +1000, matti k wrote: >> https://imgur.com/a/J6HIGpZ >=20 > It does show "available" networks, but not transmitting > capacity. Due to digitalisation of elementary schools in Germany, > enforced by the coronavirus pandemic, as somebody working for after > school childcare, a teacher and I set up LTE wifi routers and iPads. > That a network is displayed, doesn't mean that you get a reliable > connection. The school has got 5 routers and IIRC 25 iPads + > several other receivers (a digital board, smartphones and a TV). >=20 > I described my private network and mentioned that "I would be = surprised > to see it in about a 9 meter distance". Actually it most likely is > recognized by devices >=3D 9 meters away, but it's unlikely usable at > this distance. >=20 > The forums link provided by Matthias, see > = https://lists.freebsd.org/pipermail/freebsd-questions/2021-April/293682.ht= ml[https://lists.freebsd.org/pipermail/freebsd-questions/2021-April/293682= .html] > mentions why it's a tricky subject. >=20 > In school those iPads show powerful access to the LTE wifi routers, = but > often the closest routers isn't usable, while a less close router can > be used, at least with a single iPad, dunno if it stands the traffic = of > all the iPads. >=20 > The graphic provided by Matthias' Ubuntu based cellphone shows an > amazing transmitting capacity spike. It could be important to actually > get such information, not only for wifi. Depending on atmospheric > condition, there could be e.g. interferences between DVB-T > transmitters. Too powerful signals could become a PITA for somebody = who > wants to watch television, OTOH amateur radio operators might welcome > such atmospheric conditions ;). >=20 > Getting a list without reliable information about the power is quite > useless. iPads for example provide a graphic showing 3 lines. Usually = 3 > and 2 lines are for a good connection and even 1 line still could be > reliable. At home 2 lines are ok for me, in school those lines mean > absolutely nothing. You could get those lines, but the connection = still > could be fishy. > _______________________________________________ > freebsd-questions@freebsd.org mailing list > = https://lists.freebsd.org/mailman/listinfo/freebsd-questions[https://lists= .freebsd.org/mailman/listinfo/freebsd-questions] > To unsubscribe, send any mail to = "freebsd-questions-unsubscribe@freebsd.org" > _______________________________________________ > freebsd-questions@freebsd.org mailing list > https://lists.freebsd.org/mailman/listinfo/freebsd-questions > To unsubscribe, send any mail to = "freebsd-questions-unsubscribe@freebsd.org"
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?91D8B6CF-753A-4A10-A505-1673059EDB64>