Testing the presence of DSL signal with an oscilloscope

AC/DCdude17 · Jul 26, 2003

Can you test for the presence of DSL signal on your phone line with an
ordinary 100MHz scope? If so what do I look for?

Thanks

John Larkin · Jul 26, 2003

Can you test for the presence of DSL signal on your phone line with an
ordinary 100MHz scope? If so what do I look for?

Thanks
Click to expand...

A big, raunchy looking signal that's clearly not audio.

John

Adam Russell · Jul 27, 2003

Well, normally the scope inputs are unbalanced and one side is tied
to the scope's chassis ground. Then in some countries (USA is one)
you have a three pin AC mains power connector that connects the
scope's chassis to an earth ground - thus if you try to look with a
common scope probe you'll unbalance the loop and most likely that
will also croak the dsl connection. Probably not permanently but
it would interrupt it for the duration of any measurements being
taken.

If the scope had a battery to power it, that would help. Some sort
of balanced input probe would also help, perhaps with some sort of
(optical) isolation (between the dsl loop an the scope itself)...
Click to expand...

I think you could rig up some kind of inductive probe.

Hank Karl · Jul 28, 2003

Well, normally the scope inputs are unbalanced and one side is tied
to the scope's chassis ground. Then in some countries (USA is one)
you have a three pin AC mains power connector that connects the
scope's chassis to an earth ground - thus if you try to look with a
common scope probe you'll unbalance the loop and most likely that
will also croak the dsl connection. Probably not permanently but
it would interrupt it for the duration of any measurements being
taken.
Click to expand...

Just use a two channel scope, put one probe on "tip" and the other on
"ring", and sum them together (or subtract one from the other-I forget
which because its been a while since I've done this kind of stuff.)

Jul 29, 2003

Hank Karl said:

Just use a two channel scope, put one probe on "tip" and the other on
"ring", and sum them together (or subtract one from the other-I forget
which because its been a while since I've done this kind of stuff.)
Click to expand...

Subtract, or flip its phase, if 'ordinary' scopes have dual inputs
these days.

Billy Y..

Testing the presence of DSL signal with an oscilloscope

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