Modern ADSL filter/splitter (left) and filter (right)

Circuit of an ADSL filter/splitter

A DSL filter is an analog low-pass filter installed between analog devices (such as telephones and analog modems) and a POTS telephone line, in order to prevent interference between such devices and a DSL service operating on the same line. Without the installation of DSL filters, high-frequency signals or echoes from analog devices can result in reduced performance and connection problems with DSL service, and the high-frequency signals from the DSL service can result in line noise and other issues for analog devices.

Typical installation for an existing home involves installing DSL filters on every telephone, fax machine, voiceband modem, and other voiceband device in the home, leaving the DSL modem as the only unfiltered device. In cases where it is possible to run new cables, it can be advantageous to split the telephone line after it enters the home, installing a single DSL filter on one leg and running it to every jack in the home where an analog device will be in use, and dedicating the other (unfiltered) leg to the DSL modem. Some devices, such as monitored alarms and Telephone Devices for the Deaf, mainly certain older models using an acoustic coupler, may be hardwired and may not easily accept a DSL filter. Some of these devices can be successfully filtered with a DSL filter or splitter, especially if the hardwired connection is converted into a jacked connection.

Protocols and specifications

• ITU G.992.1 (G.DMT),
• ITU G.992.2 (G.Lite)

See also

• Asymmetric Digital Subscriber Line

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