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If I have a DSL filter left by AT&T, and use a different ISP now, can I still use AT&T's DSL filter, or do I need to get one from the new ISP?

Do all DSL filters do basically the same thing, or does it vary by company?

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up vote 3 down vote accepted

If you're moving from POTS to POTS or ISDN to ISDN, they should be interchangeable. If you are moving between POTS and ISDN, no.

According to what I've found:

Shared Line with Filters. Again, for some DSLs that piggyback on the POTS (or ISDN) line, the signal must be filtered or split at some point. This is not necessary for g.lite or RADSL however. The other way of doing this is by placing RJ11 "microfilters" in each phone jack -- except where the DSL modem will be. These filters are relatively small, plug-in devices and remove the higher frequencies associated with DSL. This is obviously much easier since no tools or wiring is required. This is often what is included in self-install kits, and is often referred to as a "splitterless" installation. This is a very common approach in the U.S. Note that in areas where ADSL over ISDN is provided, filtering is required also, but the filters themselves are quite different and are not interchangeable with POTS filters!

Similar microfilters are sometimes used by some telcos to reduce the excessive "whine" on the line that is produced by some modems. This is a little different approach as the filter is put on the same jack as the modem.

Found under 2.3.

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New and old providers both use the same little two-way splitter that plugs into the phone jack (then splits into 2, 1 for phone, 1 for modem). –  user156342 Jan 17 '13 at 22:42
    
You're probably fine. If you try using the old ones, no damage will be done to the equipment if it doesn't work. It will just produce more noise on the line that could potentially affect the phone and/or modem signal. –  Kruug Jan 17 '13 at 22:45
    
Why will it produce more noise? Do they use different technologies? They didn't replace the phone line, just replaced the modem. –  user156342 Jan 17 '13 at 22:48
    
It may use different technology. If they are exactly the same, no noise will be produced. If they are different, it may not filter out all of the background noise that is present on the line due to both signals being sent over the same wires. The noise would be a product of a different signal type/structure being sent by the new company than that which was sent by the old company. –  Kruug Jan 17 '13 at 22:51

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