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Coaxial cable leakage

Discussion in 'Electronic Design' started by Jeroen Belleman, Feb 17, 2009.

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  1. A few weeks ago, there was some talk about how interference
    leaks into coaxial cables, and I promised to dig up some
    (Thread "Are ferrite cable shields on coax a good idea?")

    The results are at:
    I measured only a few cable types, chosen from those that are
    commonly used around here, and which would fit into my test jig.

    I've been trying to come up with a spice model for this, with
    checkered results. The low-frequency end is easy enough: It just
    depends on the DC screen resistance. But the drop of Zt at
    medium frequencies is apparently caused by the skin effect, and
    not, as I formerly believed, due to the common-mode inductance
    of the cable under test.

    With just the cable geometry and screen resistance measurement,
    I can't predict at which frequency the breakpoint will be, and I
    don't readily know how to model the skin effect in spice, either.
    Anyone care to comment?

    Jeroen Belleman
  2. Robert LaCoste made considerable experiments into different
    grounding patterns with different types of co-ax, which is
    a closely related area. It was written up in a very recent
    edition of Circuit Cellar - December 2008 IIRC. You should
    look it up, because he presented models that explain much of
    what he measured.
  3. MooseFET

    MooseFET Guest

    Did I miss it or did you state what the termination of the outer
    transmission line is?

    Skin effect looks quite a bit like a parallel RL circuit. A many
    stage lumped constant line will match a cable fairly well if you do
    parallel RL and series RC circuits to model the increased losses at
    higher frequencies.
  4. Guest

    this may or may not help

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