DSL (ADSL) offers much higher speeds than traditional telephone line modems. This higher speed is achieved by running signals that contain much higher frequencies that the 300Hz to 3800Hz needed for analog voice communications.
The upside of this is that much higher speed is possible, but the downside of this is that the customer's network of existing analog phones can load down the line at high frequencies, weakening the broadband signals so they can carry less information. DSL line filters are fitted to stop that happening, restoring the DSL line to working at the highest frequencies it is capable of.
How to Fit DSL Line Filters For Best Broadband Speed
There are two ways to approach using DSL line filters. There an easy way and a best way. The easy way is to go round the house and fit a DSL line filter in line with each of the phones on the house phone extension wiring. To do this one usually needs as many DSL line filters as there are phones, plus an extra one for answering machines, PC telephone modems (not DSL modems), fax machines and things like EPOS credit card verification terminals. There is no problem in using a telephone multi-way adapter after the DSL line filter to feed a phone and answering machine if they are in the same room.
The DSL modem can be plugged straight into the phone line, or via an two-way adapter with a phone provided there is a DSL line filter before the phone. Some DSL line filters have a separate socket for the DSL line, saving the cost of an adapter.
This usually works fine, and means least disruption, although in can need a lot of DSL line filters. the internal house phone extension wiring still loads the DSL signal a little bit, and DSL speed may be compromised a little bit.
The alternative, and best way to use DSL line filters usually needs the customer to shift the location of their DSL modem to near where the phone line comes into the house. This can be a hassle if there is no power there, and if the customer wants to use wired Ethernet in the home they have to provide a Ethernet cable to the place where the phone network comes in.
Many DSL modems come with a WiFi access point built in, so the Ethernet requirement is not so much of a problem now, and using WiFi can protect computers against lightning strikes coming down the phone line.
Plug a DSL line filter into the first socket where the phone line comes into the house, and remove any extension wiring that runs on from there. The DSL line filter will have two sockets, one marked DSL and the other marked phone. First plug a phone into the filter and confirm that phone service is retained. Next, plug the DSL modem into the DSL socket of the DSL line filter, switch on and confirm that the modem and the phone work correctly.
Fit a plug to the extension wiring, and plug the phone extension wiring into the telephone socket of the DSL line filter. If there is a phone at this location, use either a two-way adapter plugged into the phone socket of the DSL line filter, or add a socket to the extension wiring.
The DSL modem can then be started and the extension wiring plugged into the phone socket of the DSL line filter. That was only one DSL line filter is required, and the house phone extension loading is filtered from the DSl line at the earliest point. This optimises the DSL line speed and saves money at the same time. A more detailed description of the need for filters can be found at homephonewiring.
Use DSL Line Filters for Best DSL Speed and Reliability
The DSL line filter is an essential part of the DSL system design. Some DSL modems incorporate a filter, so they have a socket marked phone on them. These modems can be used with the second strategy, but plugging the extension wiring into the phone socket of the modem. If one of these modems is used from an extension socket, then although the phone in the same room can be plugged into the modem phone socket, all the other phones one the extension circuit must be fitted with DSL line filters for good results.
Network termination sockets including DSL line filters are available. These are designed to be used with the second 'best way' strategy.
Richard Mudhar - Originally from London, now enjoying a less hectic pace of life in Suffolk, Richard Mudhar is a keen wildlife sound recordist and ...
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