Quote:
Originally Posted by Mike(Mont)
|
Interesting explanations but probably not based in existing physics.
Changeable magnetic field (as generated per detectors coils) is not the same as radio wave.
"copper wire around the house and driving it with the speaker output" does not emit radio waves, it only create changeable magnetic field (mostly inside) loop. Similar or equal as so called "ground loop" coil used in prospecting and earth survey. Neither can emit radio waves.
One simple experiment can prove us that electromagnetic field and radio waves are not the same. If you wrap your Walkie Talkie in Alu foil it can stop to emit and receive radio waves, but if you wrap detector coil (in fact most of those coil are already wrapped) in the same foil, you cannot stop magnetic field to go (out and in), through Alu foil.
Magic word here is resonance and phase. You cannot emit radio waves without resonance creating phase between radio wave components, on other side, detectors changeable magnetic field emitting and receiving coils in general does not need (PI coil par example) any resonance to emit EM field and by following phase we can only distinguish metal parts instead of propgate. There are exception (Enigma p.e.). And some detectors design are based on radio waves instead of changeable magnetic field (GPR devices, some mine detectors..).
But radio waves are composed from magnetic component too. This why ferrite antenna works. As Geo explain it aspirate nearby magnetic (as all ferromagnetic in general) field lines and this way strengthen radio signal at given location:
More reading:
http://physics.stackexchange.com/que...-really-genera