Testing the presence of DSL signal with an oscilloscope

[AC/DCdude17]

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]

On Sat, 26 Jul 2003 11:07:55 GMT, AC/DCdude17
<JerC@prontoREMOVETHISmail.com> wrote:

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

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

John

 

[Adam Russell]

<abuse@MIX.COM> wrote in message news:bfum8i$9i7$1@reader1.panix.com...

AC/DCdude17 <JerC@prontoREMOVETHISmail.com> writes:

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?

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)...

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

Then there are various kinds of dsl signaling - some use several
carriers (for which a spectrum analyzer would probably produce a
more interesting display), some use ISDN style signaling (looks
like square waves, but more rounded as the loop length increases)
and there are probably some others I don't know about yet...

Billy Y..

 

[Hank Karl]

On Sat, 26 Jul 2003 19:53:54 +0000 (UTC), abuse@MIX.COM wrote:

AC/DCdude17 <JerC@prontoREMOVETHISmail.com> writes:

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?

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.

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.)

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)...

Then there are various kinds of dsl signaling - some use several
carriers (for which a spectrum analyzer would probably produce a
more interesting display), some use ISDN style signaling (looks
like square waves, but more rounded as the loop length increases)
and there are probably some others I don't know about yet...

Billy Y..

 

Hank Karl <notgiven@nothere.com> writes:

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.)

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

Billy Y..