On Mon, Aug 24, 2009 at 4:33 PM, Micha<mi...@post.tau.ac.il> wrote: > I don't have a link now but I saw a thread somewhere about the myth of > stealing power from powerlines with a large coil, and the calculation came > to the point if I remember the numebers correctly that you may be able to > run a 1.5v light bulb using several tons of copper if your are several feet > from the power line. > > I doubt wifi is any better in this respect.
The *basic* calculation is not very difficult. I believe the most powerful long- or medium-wave broadcasting transmitters have a nominal power of 2.5MW. Assume you have a 2MW transmitter 1km from your house. Assume it actually radiates 2MW of power - I wouldn't be surprised if efficiency was around 20% or so, but let's assume 2MW is actually emitted isotropically. Neglect losses (that are, in reality, very considerable), and put a round antenna with radius of 1m on your roof. Assume that your antenna collects 100% of the radiation. The result is 2MW*pi*1m^2 -------------------- = 0.5W, 4*pi*1km^2 which might be enough to light a 1.5V light bulb with a resistance of 4Ohm (assuming no losses again). Given that your losses are likely to reduce usable power by a couple of orders of magnitude compared to the above, you will *not* be able to light a small light bulb by any stretch of imagination. Looking up the effective radiated power of your WiFi router (divide the nominal power by 5 if not quoted directly) and plugging the parameters in the formula above (what's your receiving antenna size?) is left as an exercise to anyone who keeps the router's documentation in the bottom drawer. -- Oleg Goldshmidt | o...@goldshmidt.org _______________________________________________ Linux-il mailing list Linux-il@cs.huji.ac.il http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il