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Noises on Phone line when touching appliances

  1. Jan 23, 2009 #1
    Not so much an engineering question, but electrical.

    I've got a noisy phone line in my kitchen and not sure what's going on... more curious about the electrical theory than anything else.

    -when operating either of 2 light dimmers in the area, loud hum on phone line.
    -when first touching any grounded appliance, hear a click on the line as if I am discharging or something.
    -the phone is plastic all around so it seems bizzare to me that it would make any noise when touching appliances.

    Any thoughts?
    Last edited: Jan 23, 2009
  2. jcsd
  3. Jan 23, 2009 #2
    Light dimmers are notoriously noisy. 120 times a second there's a sharp turn-on edge, that splatters electromagnetic waves over the spectrum. Turned all the way on, you should notice that the noise diminishes.

    When you touch ground a high current spike occurs that takes your body to ground potential. The abrupt change in current (from zero, before discharge) is what causes the broadcasting. There are a lot of frequencies represented, so a good chance of picking it up in a circuit not shielded or filtered well enough. Apparently, it doesn't require a noticable arc to recieve it, in your phone.

    People are modeled at about 50 pF capacitance. There's also self inductance, even a straight conductor. The current actually oscillates a bit before going to zero, if the resistance isn't too high. This part of the signal has a narrower band, than the sharp, arc-over start.
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