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RF part selection for 100 meters range

Discussion in 'Electronic Design' started by Surinder, Jun 6, 2006.

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  1. Surinder

    Surinder Guest

    Hi,

    I need to have RF transmitter on a mcu board with 12 Volts supply to
    send small ammounts of periodic data to a RF reciever board connected
    to computer (via RS232 or USB).

    The range I am looking for is 100 meters with 2 or three concrete walls
    betweeen them.

    I saw some ICs with different frequency ranges.

    There will be multiple transitters in the same area so collision should
    not spoil the communication.

    What would be the suggested frequency range for such usage?
    Also what are other things to consider.

    Any particular Rx/Tx pairs using I2C or SPI or USART based?

    Any pointers on web/books will also help

    Thanks
    - Surinder
     
  2. Bob

    Bob Guest

    Even with 1watt radios you can find that concrete and steel walls
    kill your signal. I'd borrow a pair of cheap walkie talkies on 446MHz
    or 465MHz (whatever is allowed in your country) and try them
    at the location to get an idea of how well it is going to work.
    I'd also buy a single pair of data modules first and try them before
    buying lots. Running a cable to get the receiver antenna in the
    same space as the transmitters will make a huge difference.

    UHF generally works better than VHF in buildings. That means
    315/418/433MHz. You need to check what is license exempt
    in your country (or how much hassle and expense it
    would be to get a licensed frequency). 865MHz is a bit high
    but might be suitable. 100mW data transmitters on 418/433MHz
    are cheap.

    At UHF you can find it work in one spot and dosn't work
    in another spot 30cm away. The problem is that the signal
    bounces around, the direct signal and a refleted signal
    can arrive out of phase and cancel out. That is why
    wifi access points usually have two antennas.
    Multiple receivers will be required for good performance.

    Directional antennas on the fixed equipment will help.
    Outdoors you can sometimes find that point the
    antenna at the big building in the distance that the
    signal is bouncing off can work better then the direct path.
    That's a protocol issue. If you have one way comms you can
    only transmitt with a low duty cycle at random intervals, not
    have too many transmitters on a channel and accept there is
    some probablity of it not getting through for a period of time.

    If you have two way comms the main unit can poll each
    unit seperatly.

    Bob
     
  3. Surinder

    Surinder Guest

    Thanks Bob for the info
    - Surinder
     
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