Re: Faraday Cage and 1/4 wavelength sized holes

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "davep by way of Terry Fritz <twftesla-at-qwest-dot-net>" <davep-at-quik-dot-com>


>>For a Faraday cage to work for some frequency, then

>>the holes in that faraday cage must have a diameter

>>less than the 1/4 wavelength of the frequency you are

>>trying to block.

         That's one rule of thumb.
         When i was doing EMI for computers to meet
         'FCC' it was 1/10 wave.  Rather than a single
         magic number the leakage increases as the
         slot/opening gets larger.

>>If you build your faraday cage out of chickenwire, sure

>>it will keep in your arcs and lower frequency garbage, but

>>the higher RF frequencies (Ghz) will pass right through it.


>Do you or anyone else have an estimate on how many nanowatts

>the average coil puts out in the GHz range?

         An interesting question, which would be nice to
         know.  Wish i did, tho i suspect its LOTS of
         nanowatts.  (hint: in the early years, radar jammers
         were powerful spark transmitters.  Granted, they
         were optimized for it, and at modestly lower freqs.)
         If I Recall, cell phones (mostly?) are in the
         800 MHz region.

         (A useful approximation for noise output might be
         to fire up a coil, then walk away with cellphone
         in hand until signal is acquired.  There would be
         a huge variation, due to power variation, incidental
         nature of 800MHz output, etc.  (cut to THAT TV
         commercial:  Can you hear me now?  Can you hear me
         now?  8)>>)

 > Anyone with a spectrum analyzer?
         Agreed.  Or a cell phone, or 800MHz scanner?

>Is fine level of screening really needed, or is this

>"swatting gnats with a sledgehammer"?

         Varies with coil power, detail wiring, etc, etc.

-- 
         best
         dwp

...the net of a million lies...
         Vernor Vinge
There are Many Web Sites which Say Many Things.
         -me