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fast pulse radio transmission

Discussion in 'Electronic Design' started by sergio108, May 8, 2008.

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  1. sergio108

    sergio108 Guest

    Hi All.
    I want to find a transmitters-receivers or transceiver can be used in
    our project.
    We are developing a project where we need to send and receive random
    asynchronous digital TTL pulses (5 to 10 microsecond wide) without
    delay trough RF at a variable rate from 10000 (1e4) to 100000 (1e5)
    pulses per second over 0.5-1Km area, these random pulses do not comply
    with any standard like RS-232.
    Better if the system is full duplex although half-duplex will work in
    some cases.
    We can use IC but radio modules seem to be easier to implement.
    We are considering also to use wireless video,
    One last think. We need to implement at least 3 simultaneous
    transmission so we need 3 different frequencies
    Regards
    Sergio
     
  2. I did a somewhat similar thing a while ago, but at much slower speeds.
    Essentially, I used two slightly different frequencies at the transmitting
    end, one for a "high" signal and one for a "low" signal. On the rx end, I
    fed this into a PLL (4046 in this case - like I said, slower speeds :) ).
    The loop back of the PLL was then AC-coupled to two half-wave rectifiers
    (one "positive", one "negative") feeding into Schmitt triggers, which then
    drove a set-reset flipflop.

    The idea was that on a transition from one frequency to another, the
    feedback loop of the PLL jumps in either the positive or negative direction
    as the PLL tracks to the new frequency. The AC coupling was needed in my
    case because the oscillators were shoddy and drifted all over the place
    making a pure level detection scheme unworkable. Making this work requires a
    lot of careful hand tweaking of the components, and quite possibly won't
    scale up the the switching speeds you need. There's probably some
    off-the-shelf parts that would do the job much more reliably and with less
    hair loss :)
     
  3. sergio108

    sergio108 Guest

    Thanks michael for your answer.
    I would like to know more about your project.
    I have a few questions like:
    What frequencie range, did you use?
    How did you generated those frequencies?
    So any further information is very much welcome.
    Best regards.
    Sergio
     
  4. Bob

    Bob Guest

    You say "without delay". 1Km at the speed of light takes
    3.3microseconds.
    There will be a finite delay in the receivers, filters don't respond
    instantly.
    Without knowing what on earth you are doing we can't say if that is
    signficant. From your other post about very accurate monostables
    I suspect that jitter may also be an issue.

    You appear to be posting from a university in Tenerife (a spanish
    island)
    so I'm guessing you are either a student or an acadaemic.
    Perhaps if you tell us what you are trying to acheive someone will be
    able to suggest a better approach to the whole project.

    Bob
     
  5. Tom Bruhns

    Tom Bruhns Guest

    I second what Bob wrote...let us know what you are actually trying to
    accomplish and we can perhaps suggest other ways, better ways, of
    doing it.

    I would add some more questions: at the receiving end, how accurately
    do you need to resolve the pulse width? Can the pulse be repeated, or
    do you have only one chance to properly detect it and decode it?

    Many (most??) RF transmitter/receiver ICs these days target specific
    modulation schemes. It seems like what you want is just wide
    bandwidth modulation that is capable of just two levels. You could
    use either amplitude or frequency modulation: on-off keying, or
    frequency-shift keying. The data rate and pulse width dictate the
    required modulation bandwidth, which in your case is not extreme.
     
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