[Gllug] Faraday Cage

[Chris Bell]

On Fri 16 May, t.clarke wrote:
> 
> Gosh this is all jolly educational stuff - we should have more of this sort
> of thing, maybe, and less about boring old computers ?? !!
> 
> I seem to recall reading somehwere that this faraday cage thing only works
> if the aperture size of the holes in the cage are smaller than the wavelength
> of the RF energy  - so mobile phones will still work in jail/gaol cells ??
> 
   High frequency radiation can do some very unexpected things, so the
interior dimensions and the hole dimensions are very important. Waveguides
are pipes whose dimensions are accurately matched for the frequency,
although both aerial and waveguide dimensions are slightly different from
the tuned wavelength because of wave distortions known as end effects. A
shaped piece of ferrite can be placed inside a junction box linking three
waveguides to cause phase changes, the result is that all radio frequency
energy rotates around the box in one direction only. This allows a
transmitter and receiver to share the same aerial without the receiver
getting blasted by the transmitter, they just need to be tuned to very
slightly different frequencies to allow two way transmission. The same
rotator can also be used for two transmitters or two receivers to give two
channels in the same direction.


-- 
Chris Bell



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