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What does a good DSL waveform (signal) look like?

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If you have a lot of static on your phones, then you either have a bad device on the phone line, or your premise wiring is bad.

I would start by taking a close look at your POTS / DSL splitter.
Next, check with the DSL off, plug a phone straight into the main line with no other device connected and see if you still have static.
If no static on a direct connection, the problem is a device or your wiring.
If you have static on the incoming line, the problem is between your building and the central switch.

My guess is that you will find either a phone cord that has been rolled over by a chair or pinched in a door. Or, a line in a wall that has been rubbing on a staple for years.

Taking a quick review of DSL technical data, a low frequency spectrum analyzer is going to be a better tool than a scope to look at the DSL signal. The signal can vary between 26 KHz and over 1 MHz.

While this article is for designing DSL receiver circuits, it does provide decent technical data.

One other point, the phone signal is balanced and most scope inputs are unbalanced. To see a signal of any value you either need an isolated scope with a differential input, or a 2 channel scope that allows you to view the sum or difference of the 2 channels.