Afghans Build Open Source Internet From Trash 140
An anonymous reader writes "Residents of Jalalabad have built the FabFi network: an open-source system that uses common building materials and off-the-shelf electronics to transmit wireless ethernet signals across distances of up to several miles."
Re:Any real information? (Score:5, Interesting)
The story was a little sparse on information, but one of the links goes to their page here: http://fabfi.fablab.af/ [fablab.af]. I didn't go through their docs, but I see that they do exist.
You should be able to figure most of it out just by looking at the pictures, if you have a bit of knowledge in the area.
The dishes appear to be offset parabolic dishes or troughs. Full wave for 2.4Ghz is about 4.9". So if you want to reflect that, you'd want to go smaller than 1/4 wave, or use a mesh with holes no wider or taller than 1.2". In the pictures, they appear to be using metallic window screen. You could probably get away with "chicken wire" (small mesh wire for chicken coops, so chicks can't escape). I haven't measured the spacing on those in years, but I do remember that it's small.
For your transceiver, stick your wireless USB device at the focal point, and back it with something to reflect the signal going the wrong way back into the dish, so your power won't be wasted. A curved piece of foil or some other metal will do the trick.
I'm suggesting putting the device on the focal point, rather than running an antenna from the device to the focal point, to eliminate loss from the length of the antenna wire.
"Borrowing" a satellite TV antenna (such as DishNetwork, DirectTV, or Sky), and replacing the LNB with your transmitter would serve the same purpose, but it will be more obvious. At a distance, window screen is effectively invisible.
If I remember the DefCon contest winners for long range wifi correctly, they used old C/KU residential dishes, with their transceiver at the original focal point. From what I understand, there is an effective size limitation, so going from 3 feet to 15 feet wide won't necessarily help your situation. A 100 foot wide antenna won't have an advantage over a 5 foot wide one, and you may degrade your signal due to receiving extraneous noise.
If you're crafting it yourself, you have to calculate your focal point. If you're using a previously used parabolic dish, the focal point has already been found for you.
You may have to mess around with polarity a bit. I believe most wifi operates with a vertical alignment, but does seem to survive ok with horizontal alignment. If you're going for long range service, getting the correct alignment is key.
When you're working with a target antenna miles in the distance, it's helpful to have a good telescope to find the correct direction. Fine tuning is easy enough by hand with a decent signal strength app (assuming your transceiver supports it). I've done it with good tools, and even just with Netstumbler. Move it around slowly until you reach maximum signal strength.
I've used professionally made antennas before. The longest term one was a 24dB parabolic at my house, and a 14dB panel at my office. The range was only 1/2 mile, but both sides reported 100% signal strength. That was very impressive, since they couldn't even get over 80% when they were within close proximity to each other with standard antennas. I ran with that for over a year, until our office moved. I was very happy having my own person T1 at the house, after office hours.