On Thu, 25 Oct 2007, John Winterflood wrote: > thomas malloy wrote: > As Jed pointed out, a pair of heavy iron frying pans might make a superb > Faraday cage.
Yes, and they solve the problem of shielding low-freq magnetism. For example, to well shield the magnetic component of 60Hz you'd need many inches thick of copper. > Robin van Spaandonk wrote: > > ... Note that Tesla lit light bulbs 25 miles away, with no wires, > > using only the ground as common medium. ... > > As I understand it there were two conductors - the earth and the > ionosphere. And Tesla said as much in later articles, though Tesla thought that the stratosphere was more than conductive enough. "Sending through the ground" was using the ground as a single-wire conductor, and NOT sending energy through the ground. (The EM energy goes through the space above the ground.) > The ionosphere was coupled to capacitively using a tall > mast and high frequency and voltage oscillations. There may have been > some ionospheric resonance involved also, but the whole process is not > something that is really known about and AFAIK has never been done since. In recent years a couple of NASA engineers studying VLF discovered a way to very precisely measure the Shumann resonance (Tesla earth resonance.) They found that the "known" Q-factor for various earth-resonance spectrum lines is wrong, and that they're really up in values well above hundreds. One of the long-standing objections to Tesla's broadcast power scheme is that Shumann resonance Q is eight or below. It turns out that this was an artifact of older 1960s instrumentation which had a Q-measurement capability limited to values around ten. So now the main problem with Tesla's scheme is how to broadcast power at extremely precise VLF frequencies... frequencies which wander with time over a scale of minutes. (But then, Tesla in essence was claiming to be using the Earth as the main resonant tank circuit of a vast RF oscillator.) (((((((((((((((((( ( ( ( ( (O) ) ) ) ) ))))))))))))))))))) William J. Beaty SCIENCE HOBBYIST website billb at amasci com http://amasci.com EE/programmer/sci-exhibits amateur science, hobby projects, sci fair Seattle, WA 425-222-5066 unusual phenomena, tesla coils, weird sci
