What Is a 2Wire DSL Filter?

A DSL line filter removes noise on your phone line generated by your DSL modem, such as the 2Wire gateway. DSL modems use a different frequency than what is used through regular calling, which allows you to use the phone while connected to the Internet. Sometimes, if you have devices other than the modem plugged into that line, you get line noise. This noise is both an annoyance to you and a possible interference to your Internet connection.

An Internet service provider using 2Wire products may provide you with 2Wire DSL filters when you subscribe to its service. For example, AT&T, an ISP that offers DSL service through the 2Wire gateway, provides its customers with these filters. There are several single filters, and one dual filter. The dual filter allows you to plug the modem and another device into the same jack, and a single filter allows only one device to be plugged into the jack. You plug the dual filter into the telephone jack intended for the DSL modem. Plug the modem itself into the "DSL" port on the filter, and any other device you wish to share that jack into the "Phone" port on the filter. Connect all the single filters into other jacks using the same line as the modem, and then plug devices into those filters. Don't plug your 2Wire gateway itself into either the single filters or into the "Phone" side of the dual filter. Doing so erases the gateway's signal, meaning no Internet connection.

Depending on how you obtain the modem, you might not receive the filters with your 2Wire gateway. If you have an extensive number of telephone jacks, it's also possible that you ran out of filters. However, you can get more filters separately. For example, AT&T sells 2Wire DSL filter kits to its customers who subscribe to DSL service through AT&T and connect through a 2Wire gateway. These kits cost $15 as of June 2011 and come with one dual filter and three single filters.

While the filters used with your 2Wire gateway can be useful, there are several circumstances under which you shouldn't use them. AT&T itself also recommends avoiding plugging more than five devices into any single telephone line to avoid overloading the line and causing interference. By not overloading your line with devices, you help to ensure optimal strength for your DSL connection. A single phone line can be split by a technician before it enters your house, meaning one half is dedicated to your modem while the other can be used for all other devices. If you had your phone line split, then the DSL filters become superfluous because your other devices are no longer connected to the part of the line used by the modem.