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"Insanely Exotic Modulation Tricks"

Discussion in 'Electronic Basics' started by Radium, Jul 21, 2007.

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  1. Radium

    Radium Guest

    John Larkin wrote in
    Just what are those "insanely exotic modulation tricks"?
  2. kell

    kell Guest

    What, you've never been to a strip club?
  3. John Larkin

    John Larkin Guest

    Multiple-level quadrature modulation, "constellation modulation", is
    most common for packing lots of bits per Hz of bandwidth. The more you
    pack, the better the s/n ratio has to be. Read up on Shannon.

  4. Radium

    Radium Guest

    On Jul 21, 1:28 pm, John Larkin
    In theory, could Quadrature Modulation and Constellation Modulation be
    used to give dial-up modem connections around the same fast speeds
    provided by Broadband cable modems?
  5. John Larkin

    John Larkin Guest

    Dialup used to be 300, 1200, and finally 2400 baud using fairly simple
    modems. Advanced modulation tricks (qam or multicarrier, with adaptive
    equalization) were used to push dialup to 56K. That's about the limit
    for dialup, because the signal bandwidth and s/n ratio are inherently
    limited by the telephone company voice channel hardware.

    DSL does better because it hiacks a fairly short pair of wires
    directly from a substation to your house, and doesn't go through the
    general telephone system.

    Shannon's theorems establish rigid limits on what is possible, given a
    communications channel of a given bandwidth and signal-to-noise ratio.

  6. Radium

    Radium Guest

    Could the telephone companies discard their present devices and build
    new hardware that can provide frequencies ranging from 20 to 20,000 Hz
    [instead of 300 to 3,000 Hz] and 120 dB [instead of 40 dB] dynamic
    range? Or what that be not worth the time, energy, and money?
  7. John Larkin

    John Larkin Guest

    Why would they do that?

  8. Radium

    Radium Guest

    Because the human auditory system perceives 20 to 20,000 Hz and has a
    dynamic range of 120 dB.
  9. Don Bowey

    Don Bowey Guest

    Yes, but there is no realistic demand for that in message service. Radio
    and TV stations often order 20 kHz channels for broadcast service.
    Equiptment is available for that type (point-to-point, a.k.a. Private Line)

    For message service, including Cellular, some Common Carriers and private
    networks use Low Bit-Rate coded channels to get more bang for the bucks.
    For message use most people can't perceive a quality difference between
    coding to 32 kbit/s vs 64 kbit/s.

    You're pushing an old horse nobody wants.
  10. Don Bowey

    Don Bowey Guest

    Just because something can be done, doesn't mean it should be done. Who
    would pay for the change-over?
  11. James Beck

    James Beck Guest

    If they were to do that, why not drop the whole analog audio on wires
    and switch over to fibre or some kind of data channel?
    Kind of a long road to take to get to the same destination.
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