[clug] Telephone line voltage

Mike Carden mike.carden at gmail.com
Sun Sep 5 18:56:29 MDT 2010

Curioser and curioser (said Alice).

I'm inclined to agree that something peculiar is happening in
Measurement Land. That a signal is present imposed on a DC offset is
what's to be expected for ADSL, but the oddness of a meter seeing an
'AC' present in one polarity but not the other suggests that a meter
is the wrong tool for the job.

To really figure out what's going on, a decent CRO and an isolation
transformer are needed. The tranny is essential because your CRO will
happily try to ground the phone line via its power cord otherwise and
that would be Bad.

Aside from a smidgen of curiosity, I'd tend to side with Telstra here.
If it works as it's meant to, there isn't really an issue.


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