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Pulse emitter long range data comm?

Discussion in 'Electronic Design' started by Day Brown, Mar 9, 2007.

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  1. Day Brown

    Day Brown Guest

    It seems that Zeners could be used to just clip the steepest part of a
    sine wave and port that power to a Yagi tuned to resonate with the
    effective frequency.

    Which is to say, put out a series of pulses, either pos or neg, zero
    as neg, 1 as pos. No carrier wave. No IF. No conventional AM/FM/VHF/
    UHF tuner would pay any attention to it.

    I like living in my neck of Ozark woods, but none of the commercially
    available long range wireless communication devices can penetrate the
    canopy. When the wavelength gets down to the length of pine needles,
    thru put is zero.

    The 1/4 wavelength of 200 mhz is 37.5 cm, longer than any pine
    needles. Which seems like it could be turned into 200,000kbps, and
    even with error correction give me as much as my LAN port can handle.

    But I would havta gate it with a mosfet or something. Then detect it
    on the other end. Zat reasonable?

    It's called ultra-wideband: although you may have over-simplified it.

  3. Bob

    Bob Guest

    The steepest part of a sine wave is at the zero crossing point.
    I think you mean the highest amplitude.
    Hmm, I'm not sure what the point of trying to square the sine wave.
    Why not just use a sine wave at the resonant frequency of the yagi,
    or just generate square pulses with the right period.
    Squareing a sine wave is mainly going to result in a signal with
    energy at multiples of the original frequency, the third harmonic
    being strongest. Tehh yagi isn't going to work very well at three
    times its operating frequency, the radiation pattern looses
    directivity and you won't get a good impedance match.

    If you want to multiply up to reach the yago frequency the usuall
    active multiplier circuits in radio comms books are likely to be more
    You need a low noise amplifier on the front end of the reciever.
    The problem is that the wider the bandwidth you are trying
    to receive at once the more thermal/atmospheric/electrical noise
    you will pick up and you have to get your signal back out
    of that noise.

    Picking up a single pulse thats been band limited by the
    yagi in amongst 10's of MHz of WHF background noise needs
    a lot of signal to get a worthwile s/n ratio. With
    practical transmitter power and typical path loss encoding
    a bit as a single pulse is generally not practical.
    The maximum data rate of a radio link, assuming a perfect
    encoding scheme, can be calculated with Shannon's law
    which gives max bit rate from channel bandwidth and signal
    to noise ratio.
    Wifi for example does 11MBps or more in a 30Mhz wide channel
    but needs a fairly high signal to noise ratio.

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