At 06:38 AM 6/27/04 +0200, Thomas Shaddack wrote: >If the phone is shielded, it can't transmit/receive, which makes it rather >useless. :(
When you don't want to use it, why should it not be useless? >There is one potential landmine as well; the inherent ability of any >device containing resonators to behave like a crude RFID tag. I heard >somewhere, and my memory may be failing, that it is possible to irradiate >the phone with the frequency of the cellular band, and it faintly >resonates and returns back its own echo, which has minute variations given >by type, manufacturing tolerances, and possibly age of the phone, giving >it a kind of unique signature. (This could potentially apply also to >radios and transceivers. Does anybody have any idea if it is possible to >do such kind of "active fingerprinting" of rf devices? This way it should >be possible to detect even powered-off devices like hidden transceivers or >body wires; take a transmitter, sweep the spectrum, and watch echoes on >the receiver - there could be peaks on the frequencies of the tuned >circuits inside the examined device.) Your "second order effect" physics is on target. Nonlinear devices generate harmonics when tickled. All devices vary and have characteristic RF signatures. I read something about that recently somewhere, but memory fails. >Question to RF heads here: could it work? I'm not an Elmer but I pretend to be one on the internet.