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Telephone line model

Discussion in 'Electronic Design' started by behzad, Oct 24, 2004.

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  1. behzad

    behzad Guest

    Hello all
    Does anybody knows a RLC model for telephone line?
    I need to simulate a SLIC in a real environment so need spice model
    for telephone line.

  2. Dbowey

    Dbowey Guest

    What gauge? 22, 24. 26? Mixed gauge? Is any bridge-tap permitted?

    <A HREF="">Wilcom Inc. - Test Equipment

    You may want to look at the T-240.

  3. Tim Wescott

    Tim Wescott Guest

    That gives you a physical model, but how do you connect the darn thing
    to a SPICE simulation?

    I do not think a real telephone line is going to be amenable to
    simulation with a simple RLC. It's going to act like a transmission
    line, with a characteristic impedance somewhere centered around 100 ohms
    but varying widely from one to the next, a widely varying reflection
    coefficient, a great deal of loss, also varying, and with a length that
    can be anywhere from a few feet to a few miles. In addition you'll have
    some bonus signals injected from neighboring lines, free of charge.

    Aside from that it should be a snap to simulate.
  4. Easy. Spice has direct support for transmission lines.
    Spice has a real T line that has RLC parameters.
    This is a bit more trickey but it can be modelled.

    Kevin Aylward
    SuperSpice, a very affordable Mixed-Mode
    Windows Simulator with Schematic Capture,
    Waveform Display, FFT's and Filter Design.
  5. Robert Baer

    Robert Baer Guest

    I believe that WeCo specified 500 ohms, and that all modem and phone
    balun transformers are speced at 600 ohms.
    For short length simulation (even in real life), a simple RLC will do.
    When at Fairchild, we made a tester for a tone generator chip for a
    MaBell supplier, and had to use an RLC network to simulate the line, for
    proper testing.
    The inductance was "substantial" (in the henry region), and ordinary
    on/off switching of an automatic tester would have required many seconds
    for stabilization of inductor current - thereby severely restricting
    test thruput to unacceptable levels.
    Unfortunately, that was a loooooong time ago, and i do not remember
    the inductor value.
    However, the phone line is 48-50V open circuit, and one can readily
    measure the short circuit current, to give the total series resistance.
    Look at loop simulator circuits as provided in part 68 of the FCC
    Rules and Regulations.
    From some rather old books i have:
    1) Page 29 of The Master Handbook of Telephones (Tab Books 1981)
    Tip to R2 to inductor (L=>10H, Rl) to Vbat to Ring in parallel with
    Tip to C1 to R1 to Ring.
    Vbat min=42.5V, max=52.5V; R2+Rl variable from 400 ohms to 1740 ohms.
    No notes seen for R1 or C1.
    2) Page 39 of You & Your Telephone (Sams 1980)
    Shows network circuit diagram GIF available on request). [[C1 is
    about 2uF]]
    3) Other books i have give no schematics or equivalents.
    If you look at old telephone poles, note the wire spacing; it is a
    transmission line!
    Getting dimensions (wire spacing and wire size) will allow one to
    derive the impedance.
  6. Does it support RLC parameters that are a function of frequency?

  7. Roy McCammon

    Roy McCammon Guest

    which side do you want to simulate?
  8. Roy McCammon

    Roy McCammon Guest

    But alas, we also need G and all four are functions of
    frequency though C and L are not greatly varying.
  9. Tim Wescott

    Tim Wescott Guest

    The recommended piece of equipment is a physical thing that you hold in
    your hand, not a subcircuit file. Which plug on the back of my PC is
    designed to connect this box to SPICE, and where do I get the necessary
    drivers to make it work? What circuit cards do I need to type into a
    SPICE program to make it interact with a physical thing? Doesn't the
    "S" in "SPICE" stand for "Simulation"?
    I'm sure that a telephone line can be modeled in SPICE -- I was just
    pointing out the difficulties in hopes that someone who'd actually done
    it would be willing to cough up a model.
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