[Freedombox-discuss] [HacDC:Byzantium] Re: Serval Mesh Extenders

haxwithaxe me at haxwithaxe.net
Sat Jul 13 17:56:41 UTC 2013

there is also a technique used by hams which is to have an antenna
mounted externally to the structure you are in and run a wire to the
inside where the radio is. when you go to leave the building just swap
the building mounted antenna lead for your mobile antenna and walk off.
UHF and VHF antennas are very, very easy to make. if you can find a
chimp that can read a tape-measure (me) it can make an antenna from plans :P
those bands are very forgiving of the transmitting antenna's design, or
lack there of, compared to the >1GHz bands.

> Although pretty much line of site, as it only bends
> slighty as the earth curves.
again just to be clear LOS in this case isn't the same as for 2.4GHz.
many more things that physical objects can't get through are transparent
or more transparent to UHF and VHF than 2.4GHz.
in general the higher the frequency (shorter the wavelength) the more
the radio waves act like we would expect visible light to behave (except
with water which is transparent to a grabbag of frequencies including
some visible light).

On 07/13/2013 08:02 AM, Jack Wilborn wrote:
> Amateur radio has been using Packet UHF communications for decades, I
> used it to communicate with the space shuttle many times during it's
> thousands of orbits around the earth.  That should give you some idea
> about i's range.  Although pretty much line of site, as it only bends
> slighty as the earth curves.  It's dependable and part of that is the
> frequency not so much the mode.  It also helps that we can use much more
> power and most of us use beam antennas to reach out there as far as
> possible.
> Most of this was 144 Mhz (2 meter band)...
> That's something that the mesh people need to look at is the
> distribution of the signal.  You can get antennas that will let you
> direct it to different widths such as a 20 deg or 180 area, making the
> signal twice as strong in 1/2 the direction available.  If you are on
> the outskirts you direct most of your signal to where you have the
> majority of users.
> Jack
> On Fri, Jul 12, 2013 at 11:59 PM, haxwithaxe <me at haxwithaxe.net
> <mailto:me at haxwithaxe.net>> wrote:
>     On 07/12/2013 10:02 AM, Eugen Leitl wrote:
>     > ----- Forwarded message from John Gilmore <gnu at toad.com
>     <mailto:gnu at toad.com>> -----
>     >
>     > Date: Thu, 11 Jul 2013 17:13:15 -0700
>     > From: John Gilmore <gnu at toad.com <mailto:gnu at toad.com>>
>     > To: Paul Gardner-Stephen <paul at servalproject.org
>     <mailto:paul at servalproject.org>>
>     > Cc: freedombox-discuss <freedombox-discuss at lists.alioth.debian.org
>     <mailto:freedombox-discuss at lists.alioth.debian.org>>
>     > Subject: Re: [Freedombox-discuss] Serval Mesh Extenders
>     >
>     >> The idea is that it uses the UHF packet radio to mesh over greater
>     >> distances than is possible with Wi-Fi, the trade-off being lower
>     bandwidth.
>     > PPS:  "Mesh doesn't scale over radio." is the 5-word summary of my
>     > experience. Merely making mesh work over wired connections is still
>     > a hard research problem that nobody has great solutions for.
>     mesh over wired networks is kinda silly. mesh over wireless is far more
>     useful and has been around for more than 20 years, and has gotten heavy
>     improvements since wifi has become popular.
>     if you expect every single device to be a mesh node in the same
>     collision domain within range of each other of course it won't work :P
>     in a weird way mesh doesn't scale _down_. if you have a one room mesh
>     with a chatty protocol it's going to talk itself into the ground like
>     the OLPC implemetation of the pre802.11s protocol. if you use the mesh
>     like a normal network is used (outside of classrooms and conferences) it
>     will generally work fine. if you have it spread across a large city and
>     to outlying islands of that city then it still works fine.
>     (see the Athens mesh, and Freifunk)
>     if you have a mesh infrastructure and non-mesh distribution at endpoints
>     you can use different collision domains for the mesh and user networks.
>     wifi sucks when there is no 100% clear line of sight (as in not your
>     rooftop antenna), end of story. UHF works better than wifi given a
>     partially obstructed line of sight (keeping in mind that is unobstructed
>     for that particular chunk of spectrum not physical objects ... which for
>     2.4GHz those are the same :P).
>     with slightly clear line of sight UHF can go miles. if you set the
>     device in a window that is enough for it to get signal through from the
>     inside to anything in a ~90deg cone of the window. it obviously isn't
>     ideal, but it's cheap and UHF-based extenders could be as good as a
>     similar system using only wifi, for much fewer units, and require less
>     people to collude or less unattended units strewn across a rural area.
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