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Cable tracing through a building

Discussion in 'Electronic Repair' started by [email protected], Nov 19, 2013.

  1. Guest

    We have a piece of RG6 Quad in one area of a building and we can't seem to find the other end of it. I thought that I knew where it went as I installed all these cables, but it's just not there. I have a small tone generator and an inductive probe that work well on unshielded wire, but attempts at using this on shielded cable have always been a problem. I've been thinking of trying to set my old HP200CD audio oscillator to 1KHZ and really crank it up and feed it into the cable. The 200CD will output a respectable signalacross 600 ohms, (naturally I'd be using it unterminated here), and I wonder if I'd be able to pick it up through the cable then?

    The only other thing I can think of,(and this is probably not very practical) is to inject a high enough RF frequency into the cable at a level where it would egress. Perhaps I might be able to see this on my spectrum analyzer. Of course I realize that the superior shielding of the quad cable is working against me here too.

    I know that there must be equipment designed to do this, but I'm not reallyin a position to make a purchase like that. Does anyone have any suggestions for finding this cable? Thanks, Lenny
     
  2. Leif Neland

    Leif Neland Guest

    John Robertson sendte dette med sin computer:
    I guess he wants to use the cable again, without having the insulation
    burnt by sparks

    But I'm using the same trick when finding breaks in the loop for my
    automatic lawnmower.

    I can usually hear the spark even if it is underground.

    I'm using an electric cattle fence generator, around 6kW.

    Leif
     
  3. amdx

    amdx Guest

    This won't help the OP, but it is a technique I have used to find
    buried coax several times and it has worked every time.
    With a portable AM radio, position the radio on it's backside and
    rotate it until you find a null in the audio. This is how you want to
    lay it on the ground, now as you move it over a coax in the ground the
    radio signal will be disturbed and the null will be lost and audio will
    appear. I have followed 40ft of coax with this method. I love it, saw it
    somewhere on the net.
    Mikek



    Tune a portable AM radio to a *station that when you rotate and find
    the null, (all audio disappears)
     
  4. Guest

    I really like the AM radio idea in conjunction with a noise source, and while I don't have a Ford coil around I'm sure that I could come up with a coil and some type of interrupter to do the spark. However as was mentioned inthe thread, using 15KV I don't want to blow a hole through the cable either. That might make a few nice unwanted notch filters for God only knows what frequencies...

    The EM door buzzer sounds like a pretty non destructive idea, but how wouldI connect it to the cable?

    I just noticed Jeff's idea of using an RF frequency, modulated it seems with some sort of waveform on the AM band. I especially like that idea and in fact was just considering throwing it out there when you posted it Jeff, but with one exception. I have a function generator, but I don't know if it will cover this band. I also have an AM signal generator that unlike my boat anchor Marconi, is portable. I can internally modulate it at 400HZ. I understand the procedure you've outlined reversing the shield, levels, etc, sowhy couldn't I use a standard AM signal generator?

    The answer to the other suggestion posted about using two shields is also interesting, however the term "quad" does not describe four cables but rather a description of the shield on one cable. Lenny
     
  5. "Leif Neland" wrote in message
    Did you mean 6kV? You aren't trying to grill the beef on-the-hoof!
     
  6. Is the destination end "dangling" -- that is, exposed and not connected to
    anything?

    If so, just stick a battery on the other end and start measuring.
     
  7. Guest

    I have gotten a lot of great ideas guys. I'll give it a shot. Thanks for all the help. Lenny
     
  8. Guest

    Don't discount the possibility that somebody cut it short and shoved
    the end back into the wall, or up above the suspended ceiling, or
    whatever. If they shoved it back in the wall and that wall has since
    been painted or otherwise remodeled, there might not even be a hole in
    the wall anymore.
    Try putting the -/black lead of the tone generator to earth ground (like
    powerline ground at an outlet) and the +/red lead to the *shield* of the
    RG6. Then use the inductive probe like normal.

    Matt Roberds
     
  9. Bob F

    Bob F Guest

    I might be a good idea to test for continuity to ground at the unknown end
    before some of the suggested tests to find out it somethink is connected to it.
     
  10. RobertMacy

    RobertMacy Guest

    some usually gets through even if 'grounded'

    However, better if possible to inductively couple to the shield, less load
    for your source. Or, just tap into the shield about a foot away from the
    grounding.
     
  11. Guest

    Lenny, please be sure to tell us what you end up doing and if you are successful.
     
  12. "dave" wrote in message
    My point in suggesting DC is that there's no inductive coupling to confuse
    identification.
     
  13. josephkk

    josephkk Guest

    You might try using 10 kHz and exciting both core and shield against
    ground. It might work better.

    ?-)
     
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