What are DSL Phone Filters?
For subscribers to the popular Digital Subscriber Line high-speed data service, DSL filters are likely installed on every voice telephone throughout the home. Allowing voice and high-speed data service to coexist on the same pair of copper telephone wires, the devices filter sounds to keep one frequency range from overlapping into another. Without these handy devices, DSL service would be greatly impeded or, in many cases, may not function at all.
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Function
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DSL filters work by, essentially, acting as a filter to keep voice and data conversations from encroaching into one another's frequency ranges. High speed data transmission through Digital Subscriber Line (DSL) service is performed in the upper frequency bands capable of being carried by standard copper telephone wires. Since voice conversations rarely make use of that frequency band, the high speed data transmission can peacefully coexist on the same telephone line with an ongoing voice conversation. Occasionally, however, a "buzz" or "static" from the DSL transmission may bleed into the audible telephone conversation, or high pitches in the voice range may edge into the frequency range inhabited by the DSL service. To prevent this overlap, DSL filters use an electronic component known as a "band pass" filter to remove one conversation from the other.
Types
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DSL filters are available in a variety of forms, many of which are quick and simple for consumers to install. The most basic form of DSL filter is the "in-line" filter. In this configuration, a telephone plugs directly into the DSL filter rather than into the wall; in turn, the filter plugs into the wall to complete the telephone circuit. When a voice call occurs, the in-line DSL filter keeps the voice and data conversations separate.
A second kind of filter is built into the telephone jack itself, requiring no additional in-line components. This filter functions the same way as the in-line filter, but is physically located inside the telephone jack for a tidier appearance and a reduced likelihood that the added telephone line component may be pulled out of the jack or otherwise damaged.
Finally, a device known as a "duplex adapter" plugs into a standard telephone jack and splits that single jack into two available ports: one for the DSL modem and one for a standard telephone connection. The filtering is performed inside the duplex adapter, and the conversation is merged into a single, filtered telephone connection. -
Price and Availability
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DSL phone filters are inexpensive and readily available. Easy-to-install in-line filters can be purchased for around $5 as of 2009 at local electronics and discount chain stores, and duplex adapters can be found in these same venues for only slightly more money. More advanced filters, like those built into telephone jacks, may cost slightly more and may be available from telephone company stores and specialized electronics retailers. Of course, all types of DSL phone filters can be easily found in a variety of online stores and ordered for convenient delivery.
Uses
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Because DSL filters keep voice and data connections separate, the filters should be installed on each telephone sharing a line with DSL service. Other data transmissions, such as those taking place between analog (up to 56Kbps) modems, also make use of the voice portion of the telephone spectrum. For this reason, any data devices---including fax machines, analog computer modems, satellite television adapters, and security systems---should also be fitted with a DSL phone filter. Finally, it is important to remember not to attach a DSL filter to the telephone line connecting the DSL modem to the wall jack. Since the filter effectively removes the DSL spectrum, installing a DSL filter between the modem and wall jack will disable DSL service.
Exceptions
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One of the most attractive aspects of DSL service is that it allows users to receive high-speed (broadband) data service over existing telephone lines. Since most users share their home or office telephone service with the DSL connection, DSL phone filters must be used to prevent interference. A relatively new offering, however, allows DSL service to enter the home or office on its own wire, completely removing voice telephone conversations from the line and eliminating the need for DSL filters. This service, known as "Naked DSL" because it is not "clothed" in voice telephone lines, connects directly to the DSL modem and does provide connections to voice extensions. Generally speaking, Naked DSL is the only DSL deployment in which DSL phone filters are not required.
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