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Ground for portable device

  1. Feb 19, 2010 #1
    Hi, Some of the ICs for a portable device I'm making need to be attached to ground. However, the device needs to be wireless so I can't ground it the way we usually do. Is there any way around this, such as a circuit that could somehow act as ground? Thanks.
     
  2. jcsd
  3. Feb 19, 2010 #2

    vk6kro

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    Unless it is a radio device where the real ground makes a difference, "ground" really just means that these points can be joined together or touched by humans without affecting the circuit operation (or the humans).

    Normally, there will be a substantial area of metal which is used for bypassing purposes.
    This may be an actual metal case or it may be a portion of a printed circuit board copper coating which has not been etched.
    Incoming shielded cables would have their shield connected to this "ground" and pins of ICs etc that were marked as "ground" would be connected to this area as well.

    Because the different areas of this ground have negligible resistance between them, they can be regarded as the same point for most circuits. For very high frequency circuits, the inductance beteen various points on the "ground plane" have to be allowed for in the circuit layout.

    In portable applications such as battery operated equipment, this metal area does not have to be connected to the actual ground or even to a mains supply ground.

    If the apparatus was mains powered, this metal case would have to be grounded in accordance with wiring regulations.
     
  4. Feb 19, 2010 #3
    Actually it's a radio device. I'm going to get an oscillator and connect it to an antenna. Would the ground for the antenna need to be set up differently than the ground for the ICs?
     
  5. Feb 19, 2010 #4

    vk6kro

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    Actually it's a radio device. I'm going to get an oscillator and connect it to an antenna. Would the ground for the antenna need to be set up differently than the ground for the ICs?

    It depends on the frequency and type of antenna. If you have a balanced output going to a matched, balanced antenna, you don't need a ground. It would work OK anywhere.

    If you have an antenna that is a quarter wavelength long, or less, then the ground connection is very important and an actual ground or a ground plane will make a big difference.
    A ground plane is either a flat area of metal (like the roof of a car) or it can be some radial metal rods just below the antenna.
    Like this:
    120px-136_to_174_MHz_base_station_antennas.jpg


    Most countries have fierce penalties for using transmitters illegally, so be warned. Don't do it.
    Get a Ham Radio licence and learn how to transmit safely and legally.
     
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