Noises on Phone line when touching appliances

[Homer Simpson]

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 bizarre to me that it would make any noise when touching appliances.

Any thoughts?
Thanks.

 

[Phrak]

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 receive 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.