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Coaxial step formulas

Discussion in 'Electronic Design' started by Michele Ancis, Jul 16, 2003.

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  1. Hi all,

    can anybody suggest me (if not telling me directly) where can I find
    some information on caluculating the effect of step discontinuities on
    coax cables? That is, when I have some 50 ohm cable and connect it to
    a 10 Ohm one, there is a step discontinuity exciting other (cutoff)
    modes: their effect can be kept into account with a shunt element,
    whose value depends on the geometric characteristics of the step. I
    would greatly appreciate if I can find some ready result instead of
    having to work my way through the math involved...

    Thanks in advance,

  2. Reg Edwards

    Reg Edwards Guest

    What range of frequencies ?

    Steps of what ?
  3. Even older than that. References below from "Millimicrosecond
    Pulse techniques" by IAD Lewis and FH Wells, 1954.

    Ref 233; Whinnery JR, and Jamieson HW. "Equivalent Circuits
    for discontinuities in transmission lines".
    Proc Inst Radio Engrs, 1944, Vol32, pp 98-114.

    Ref 234; Whinnery JR, Jamieson HW, and Robbins TE.
    "Coaxial Line Discontinuities".
    Proc Inst Radio Engrs, 1944, Vol32, pp 695-709.

    Ref 235; Miles JW. "Plane discontinuities in coaxial lines".
    Proc Inst Radio Engrs, 1947, Vol35, pp 1498-1502.

    If you don't have it, I can post relevant parts of the precis
    of Whinnery's equivalent capacitance values for discontinuities
    that were given on pages 28/29 from the Lweis and Wells book.
    However, it would be verbatim, and typed in complete ignorance.
  4. Dear Tony,

    thanks for your references, I think I can retrieve them somehow in the
    university library. This is exactly what I was looking for!

    Thanks again,

  5. Tom Bruhns

    Tom Bruhns Guest


    Thank YOU, Michele, for an interesting thread from which I learned a
    couple things. I have known for some time to realize that abrupt
    transitions in TEM lines cause local disturbances beyond simple
    impedance transformations, but was unaware of the references that
    would help explain them. So thanks for bringing this up, and thanks
    to Tony for supplying the references.

    The much more usual case is someone posting some question far beyond
    their level of understanding, so perhaps you will find it in your
    heart to forgive those who didn't take you very seriously. On the
    other hand, perhaps they (we?) will also be a little more tolerant of
    questions which at first blush appear to be out of their depth.

  6. James Meyer

    James Meyer Guest

    On the other hand, had the final explanation of the question been posted
    first, there would have been no acrimony at all.

    Especially now that Robert has passed away.

    Say what you mean, mean what you say, start at the beginning, and when
    you get to the end, stop.

  7. I don't have to forgive nobody! Nobody has made any grievance. Oops, I
    have to apologize english is not my mother language (perhaps you
    already noticed it..;-)), so what I mean is that, for me, nothing
    happened. I'm sorry if it looked like I was angry.

    On the
    The first post was written in a hurry because I needed an answer quick
    and I was beating different paths. However, I'm still convinced that
    it contains all the relevant information. I've written there of cutoff
    modes excited by discontinuities, and of equivalent shunt elements
    that can lump these effects. I haven't talked of impedance
    transformations at all.
    When I got the feedback, I saw that I had to be more detailed, but I
    still think it is largely a matter of attention. Maybe this is the way
    it is, and the next time I'll spend more time on writing...if I have
    Thank for your good advice, but I guess it is easier to say than to
    do...I will do my best as is my usual.

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