Wifi scanner for FreeBSD

[Valeri Galtsev]

> On Apr 5, 2021, at 2:12 AM, Peter Cornelius <pcc at gmx.net> wrote:
> 
> G'day, folks,
>  
> 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.
>  
> 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. 

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 “wet” 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.
>  
> 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.
>  
> Just my 2 cents.
>  
> Cheers,
>  
> Peter.
>  
> [1] https://en.wikipedia.org/wiki/List_of_WLAN_channels
>  
> 
> 
>  
> 
> Gesendet: Sonntag, 04. April 2021 um 13:35 Uhr
> Von: "Ralf Mardorf" <ralf-mardorf at riseup.net>
> An: freebsd-questions at 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
> 
> 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).
> 
> 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 >= 9 meters away, but it's unlikely usable at
> this distance.
> 
> The forums link provided by Matthias, see
> https://lists.freebsd.org/pipermail/freebsd-questions/2021-April/293682.html[https://lists.freebsd.org/pipermail/freebsd-questions/2021-April/293682.html]
> mentions why it's a tricky subject.
> 
> 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.
> 
> 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 ;).
> 
> 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.
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