EMI from a phone line

[JohnCU]

i was out in the field today with an EMI sniffer trying to locate noise getting into some instrumentation and the thing went nuts when i got near a phone line. i thought that was just 90VDC or something?

 

[Born2bwire]

Originally posted by: JohnCU
i was out in the field today with an EMI sniffer trying to locate noise getting into some instrumentation and the thing went nuts when i got near a phone line. i thought that was just 90VDC or something?

No no. The phone is an AC signal which would create EM waves.

 

[Mark R]

DSL signals go up into the MHz region.

 

[JohnCU]

Originally posted by: Mark R
DSL signals go up into the MHz region.

this is in the middle of a power plant, no DSL

 

[Modelworks]

The other thing is that phone line voltage isn't a constant cycle AC. It is usually 48VAC but when it rings a phone the line changes to 70-130VAC at 20 cycles.