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Time Domain Reflectometry

Discussion in 'Electronic Design' started by [email protected], Apr 10, 2007.

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  1. colin

    colin Guest

    You only need matched termination for when the pulse returns,
    by wich time the transistor will be fully off.

    ofc this rules out using a step.

    Most ethernet chips have TDR built in for coax connections anyway,
    even most PC ethernet ports have this feature,
    although its probably quite hard to find any software that can access it.

    Another good way is to use a single frequency at anyone time,
    and measure the standing wave voltage,
    thus avoiding any pulse smearing,
    to give absolute distance the frequency is scanned untill it passes through
    2 nulls.

    all it needs is a 1-2ghz vco and a PIC.

    Colin =^.^=
     
  2. whit3rd

    whit3rd Guest

    The absolute-max ratings aren't your concern here; the design
    uses multiple outputs in parallel to ensure that the output impedance
    of the 74AC14 is NOT limiting the current; that output impedance is
    not even remotely constant through a transition from high to low,
    or from low to high, nor is the low impedance the same as the
    high impedance (remember, those impedances result from very
    different transistors in the chip).
    The only problem with this is that a lot of gates on the chip
    are transitioning at the same time, and your power supply
    pins will require the best bypass capacitors and wiring that you
    can arrange or you'll get power-supply-droop.
    If your drive is higher impedance than the 50 Ohm cable, the
    capacitance
    dominates and you get low-pass characteristics. If, on the other
    hand, your drive is LOWER impedance than the cable, the series
    inductance dominates and you get high-pass characteristics.
    If you match the impedance, you get neither.

    'Neither' is the right answer here, because it simplifies the
    resulting behavior. You were looking for another effect, nicht wahr?
     
  3. Guest

    Ahh - the memories ...
    I dropped one out of the back of a van once doing some rental car driving on a
    gravel road ;-) Good thing we shelled for the transport ca$$$e - instant ROI!
     
  4. jasen

    jasen Guest

    another kiwi!
    most of the world won't get those. the usenet network has strategiically
    located filtering software
    that strips them out.

    You should have access to alt.binaries.schematics.electronic where they are
    allowed.

    Bye.
    Jasen
     
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