Creating a 10km wireless bridge...pointers?

[Ian Smith]

On Sat, 21 Mar 2009 06:43:01 -0600 Modulok <modulok at gmail.com> wrote:

 > I have been tasked with getting a DSL connection across about 10km of
 > no-man's-land to a rural location without internet access. Ideally,
 > all traffic inbetween the two directional antennas would be encrypted.

Best encrypted, or at least use point-to-point adhoc in bridge mode 
rather than point-to-AP unencrypted, which will surely get abused.

 > (Nice, but not entirely required.) 3Mb/s would be great! Something
 > like:
 > 
 > LAN<->BSDrouter<->modem<->Antenna<~~air~~>Antenna<->modem<->DSL
 >
 > I'm looking for general pointers of both hardware and software to
 > achieve this. I'd like to employ FreeBSD as much as is feasible. This
 > is my first WAN network project, so even newbie pointers and general
 > references would be much appreciated. (Hardware suggestions, books to
 > read, etc.) Reliability is of mild concern, simply because I don't
 > want to drive 10km at 3:00am when something breaks.
 > 
 > Tips? References? Advice?

I suggest downloading "Wireless Networking in the Developing World" in 
language of choice from http://wndw.net/download.html .. a great read, 
good coverage of theory and lots of practical advice.

If you're on a budget, a couple of (say) Dlink or Cisco APs - something 
with decent external antenna connectors anyway - in bridge mode with two 
yagi or helical antennae with >= 12dBm gain should do 10km line of sight 
easily.  With +15dBm antennae you should get (at least lower) 11g rates, 
and if you can afford 20+dBm dish grid antennae, so much the faster.

Might be worth checking out /usr/ports/net/olsrd (http://www.olsr.org/)

As others have said - avoid amplifiers, spend most on good antennae and 
cables, as short and fat as is practicable.  You'll likely want short 
pigtails between the wireless card or bridge and the longer fat leads.

cheers, Ian