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Thread: Wanting to build a faraday cage to block radio signals

  1. #1 Wanting to build a faraday cage to block radio signals 
    Time Lord
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    I want to experiment with radio waves in the 100 to 200 mhz frequency range. However, I know that it is illegal to broadcast a signal without permission.

    So, I'm wondering if I can build a faraday cage around the room I'm experimenting in, and thereby block the signal from escaping, and hopefully not be breaking the law that way.

    Furthermore, I'm wondering if I can do so inexpensively? Could I coat the inside of the room in tin foil, then ground the tinfoil to a lightning rod that I jam deep into the ground outside? Would that be enough?


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  3. #2  
    Forum Cosmic Wizard
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    Maybe you could just build it big enough to contain the transmitter.


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    Forum Masters Degree DianeG's Avatar
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    I've read that microwave ovens block radio waves, and that if you put a cell phone in a (non operating) microwave oven, it cannot send or receive anything. So perhaps if you research what they are made of, you could replicate it.
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  5. #4  
    Forum Bachelors Degree One beer's Avatar
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    Quote Originally Posted by kojax View Post
    I want to experiment with radio waves in the 100 to 200 mhz frequency range. However, I know that it is illegal to broadcast a signal without permission. So, I'm wondering if I can build a faraday cage around the room I'm experimenting in, and thereby block the signal from escaping, and hopefully not be breaking the law that way. Furthermore, I'm wondering if I can do so inexpensively? Could I coat the inside of the room in tin foil, then ground the tinfoil to a lightning rod that I jam deep into the ground outside? Would that be enough?
    A Faraday cage works because when the cage bars are less than the wavelength in question, the cage appears as solid earthed metal as far as the frequency is concerned. 200 MHz has a wavelength of 1.5m, so anything with bars significantly closer than that should in theory do the job. Foil might work, but you will need to be sure that all the strips of foil are electrically connected - aluminium can be tricky owing to its oxide layer - and don't forget the ceiling, floor, doors and windows. Only other problem might be people thinking you're weird or dangerous to have a room lined in tinfoil ! A more practical method would be to get an old microwave, as Diane suggested. The microwave will contain frequencies up to 2.4GHz, so if you could fit your experiment in one that would probably be the easiest way.

    If you needed to have wires feeding your transmitter, a small hole drilled in the side panel and use of screened cable with the screen connected to earth or chassis would not let the transmissions escape.

    Also; I'm sure you realise this, but close the door and don't turn the microwave on ! Use it dead and completely deactivated - it's just the cage you want.



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