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- Path: sparky!uunet!zaphod.mps.ohio-state.edu!darwin.sura.net!dtix!oasys!curt
- From: curt@oasys.dt.navy.mil (Curt Welch)
- Newsgroups: sci.electronics
- Subject: Re: Phone line monitor
- Message-ID: <27402@oasys.dt.navy.mil>
- Date: 11 Nov 92 15:37:50 GMT
- References: <BxGK30.K71@mtholyoke.edu> <1992Nov11.130157.21099@email.tuwien.ac.at>
- Reply-To: curt@oasys.dt.navy.mil (Curt Welch)
- Organization: Carderock Division, NSWC, Bethesda, MD
- Lines: 21
-
- I asked:
- > So, my question. How do I use a scope to look at a phone line? Do I
- > need an isolation transformer between the power and wall outlet? Or is
- > there some type of probe I could buy that would provide the needed
- > isolation?
-
- ch@eiaut2.tuwien.ac.at (Christian Kral) answered:
- >There is a simple possibillity of getting rid of this kind of problems,
- >using a two channel scope which can add both inputs and invert one.
- >If you hook up both probes to the two telefone lines, leaving the
- >GND-connectors of the probes away, you can measure simply the
- >differencial signal which is just what you want, regardless of the
- >common voltage.
-
- Yes, a few people have suggested this. (Thanks to all of you).
-
- I tried it last night and it works great. It was just a matter of
- learning how to use my scope! (I always wondered why they had
- the channel 1 + 2 add function and the channel 2 invert switch!)
-
- Curt
-