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Homebrew HV hiZ scope probe

Discussion in 'Electronic Design' started by TheGlimmerMan, Oct 20, 2012.

  1. Sjouke Burry

    Sjouke Burry Guest

    CUT

    Any car repair shop.
    Used to hook up spark plugs.
     
  2. Yeah, like dragging the center conductor out of a meter long piece of
    coax is an easy task, much less feeding another back through.

    Standard RG-8 center conductor dielectric strength is 1.5kV.and they
    are not easy to get out. Fairly tightly bound to the core media.

    Probably cheaper to find and get the right stuff.
     
  3. Fred Abse

    Fred Abse Guest

    Not any more. It has derated itself to about 12kV. It won't do 40kV
    anymore without the fluorocarbon.

    If you can get the 114 from somewhere, you can recharge it. See the manual.
     
  4. Fred Abse

    Fred Abse Guest

    Then do what I did, resistors at each end.
    Wrong. The value of 60 ohms was empirically determined from an .ac
    analysis, with the resistor values stepped. See my LTspice listing, all
    the necessary information is there, just uncomment the .step param card,
    and comment (or delete) the 60 ohm R parameter. Pick the value which gives
    the smoothest, flattest rolloff, at the HF end. Try without any resistors,
    too, you'll see what I mean about resonance.

    The value of R is *not* the Zo of the cable (which is complex,anyway).
     
  5. Is "people like that" referring to the needling method or the "way" the
    person is?
     
  6. amdx

    amdx Guest

    Root around long enough, and we'll find a pun.
    Mikek
     
  7. JW

    JW Guest

    I Woodn't.
     
  8. Guest

    Deciduously not.
     
  9. Guest

    I think you've found the root of the problem.
     
  10. josephkk

    josephkk Guest

    'It is upon the trunk that a gentleman works. When that is firmly set up,
    the Way grows. And surely proper behavior to parents and elder brothers is
    the trunk of goodness.' (Ancient Chinese. Analects, i. 2)
     
  11. Robert Baer

    Robert Baer Guest

    Sorry...mistype... cable is about 50 ohms per foot.
     
  12. Robert Baer

    Robert Baer Guest

    Resistance is about an order of magnitude higher than desired.
     
  13. Robert Baer

    Robert Baer Guest

    OOooo!
     
  14. Robert Baer

    Robert Baer Guest

    That sounds like it may be do-able.
    BUT where does that resistance wire come from? Most heaters have a
    much larger diameter nichrome wire, and i do not know where one can buy
    "plain" resistive wire like that.
    Suggestions?
    Oh, "insert" might be a bitch..one might be forced to spot-weld the
    resistive wire to the existing internal wire.
    And it ain't easy to pull out....
     
  15. Robert Baer

    Robert Baer Guest

    Reason why center conductors are virtually impossible to pull out,is
    that the insulation is hot-cast onto the wire..
     
  16. Robert Baer

    Robert Baer Guest

    Know where that rainbow is----^ ?
     
  17. Robert Baer

    Robert Baer Guest

    Excellent!! You are on a roll!
     
  18. tm

    tm Guest

    Why not make an active HV probe and have it drive a standard cable?
    Many scopes have a probe power source available with +/- 15 volts or so.
    There is plenty of room in the handle of a 1 Gohm to 10 meg 1000X probe to
    put an opamp and other parts.
     
  19. Then wrapped even tighter by a Chinese handcuff overbraid of silver
    plated copper shielding. So tightly it makes a deep fingerprint
    impression of the overbraid onto the core media. It doesn't just slide
    off either.
     
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