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2.4 GHz wired shared medium.

Discussion in 'General Electronics Discussion' started by Norpentar, May 5, 2010.

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  1. Norpentar

    Norpentar

    1
    0
    May 5, 2010
    Hi! I'm working with Wireless Sensor Networks. I'm looking for a product that allows me to connect several motes at 2.4 GHz in a shared medium. (I cannot use the air due to interferences and reflexions) All the motes connected to the ports of the product have to be able to transmit to and receive from each other, in order to simulate the beacon mode. I don't care about the delay between them, just their bidirectional capability. The motes have an SMA antenna connector by the way.

    Does anyone know something I could use for this purpose?

    Thanks!
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,270
    2,718
    Jan 21, 2010
    The problem with doing this is that you will overload the receivers significantly.

    If you can wind down the power to something in the microwatt range you may be able to connect them to a "buss" of suitable coax (maybe you can do this with a 40, 50, or 60dB attenuator on each?).

    There is a problem with delay though (and remember that c in coax is substantially lower than c in a vacuum) because if these things use 802.11, they rely on a maximum distance between nodes to detect "simultaneous" transmission. It is highly unlikely you'll exceed this though.

    There are also several other problems:

    1) you will probably end up connecting your earths together via the outer braid of the coax. This could be very nasty.

    2) you would want to have a high impedance connection between the coax and the transmitter/receiver and have only "real" terminations at the ends to prevent reflections and other badness.

    3) you still may have problems with signal leakage and reception of unwanted signals.
     
  3. NickS

    NickS

    367
    0
    Apr 6, 2010
    Have you ever designed for frequencies that high before?

    Most design practices common at low frequencies just don't translate when you are working at 2.4GHz(Matching, controlled impedance, parasitics, mathematical feasibility of multiport networks are a few of the problems you will encounter). For instance their is no mathematical solution for a matched 3 port network.

    So if this is your first design in that frequency realm then I suggest you pick up a microwave engineering textbook and read it(such as RF Design Guide by Vizmuller or Microwave Engineering by Pozar). If you are still interested after that then you may have the dedication necessary to succeed in no less than 3 tries. Otherwise you should probably walk away from this project.
     
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