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Unipolar Power Line Arcing RFI?

Discussion in 'General Technical Questions and Answers' started by N0TZU, May 17, 2018.

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  1. N0TZU

    N0TZU Platinum Subscriber Platinum Subscriber QRZ Page

    I've been tracing power line RFI noise to a couple of nearby poles. I noticed something very odd which is that the received arcing spikes are occurring at 60 Hz, not 120 Hz, and only on one polarity. (the audio of the noise was observed on the scope to make sure it was synced with line and not from some other source.)

    This doesn't seem consistent with a simple spark gap situation which ought to be bipolar. And I don't think it's coming from a semiconductor lightning arrestor because my ultrasonic detector points to other hardware on the pole.

    Any ideas on why this is occurring?

    (Yes, I did make sure it the RFI is not coming from anything in my house by running on battery, I did look at the audio from two different receivers, and the noise blankers were off.)
  2. WA7ARK

    WA7ARK Ham Member QRZ Page

    Back when I lived near overhead power lines, I have seen the same thing ( line-synced scope connected to receiver audio). Could some oxide-layer be doped with an impurity such that is becomes a Zener diode (conducts one-way, but not the other?)
    N0TZU likes this.
  3. N0TZU

    N0TZU Platinum Subscriber Platinum Subscriber QRZ Page

    Cuprous oxide is a semiconductor and these poles are 40 years old so that seems a possibility. Especially since ultrasonic indicates the source on the worst pole is associated with an area where the copper ground wire meets some other hardware and several staples. Zinc oxide could be a factor too and none of the hardware up there is shiny.

    However, I thought copper wire mostly oxidized to cupric oxide in the environment which isn't a semiconductor...
  4. G0GSR

    G0GSR Ham Member QRZ Page

    One phase arcing to earth?
  5. KA9JLM

    KA9JLM Ham Member QRZ Page

    How did you measure the polarity ?
  6. N0TZU

    N0TZU Platinum Subscriber Platinum Subscriber QRZ Page

    It's all single phase in the neighborhood. There is 3-phase along the county road and to pivots but that's almost a mile away and don't seem to be arcing when I've driven by.
  7. N0TZU

    N0TZU Platinum Subscriber Platinum Subscriber QRZ Page

    Radio audio output to one channel on the scope. 120VAC on another channel. Trigger on "line" and chop. The noise spikes only occur on one polarity of the AC.
  8. K3RLD

    K3RLD Ham Member QRZ Page

    Isn't that what all diode's do? I think zener's are just voltage limiting, no? I digress...
  9. KA9JLM

    KA9JLM Ham Member QRZ Page

    That sounds cool.

    Not sure how radio audio output is phased in relation to the AC input.

    I need to learn that trick. :)
  10. K0OKS

    K0OKS Premium Subscriber QRZ Page

    His would be in sync if the radio was picking up line noise. Or, I guess you mean the audio wave might be in sync with the positive going, or negative going portion of the mains?

    So the audio looks half-wave rectified? With a flat line where the negative going portion of the mains is?

    :eek:Have to throw in the obligatory warning for anyone reading this to never connect your scope to the mains (outlet) unless you understand the ramifications of the ground clip on the scope and the neutral line of the outlet both being mains earth referenced... :eek:

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