ADSL Help > Micro Filters

This section provides an outline of how and where to use microfilters within an ADSL broadband installation. Most of the UK's telephone lines are made from copper, which is used to connect your home or business to the telephone exchange. If the lines to your house or business are not copper (perhaps they are aluminium or fibre), then you will almost certainly not be able to use ADSL, since this technology has been designed to work with copper wires only.

Any reference to telephony equipment below includes telephones, fax machines, Sky receivers, alarm autodialers etc.

An illustration of a typical non-ADSL household is shown in Fig. 1. The copper wire from the exchange to the master socket and the extension wiring do not carry the higher frequency ADSL traffic, hence there is no problem with the telephony equipment.

Fig.2. shows the problems which could be experienced with using telephony equipment on unfiltered lines. The higher frequency ADSL signals interfere with the lower frequency telephone signals causing line discruption.

The probable scenario following a BT Engineer installation of ADSL is illustrated in Fig.3. An ADSL Adapter faceplate is added to the Master Telephone Socket, which then provides two sockets (one unfiltered for ADSL and one filtered for telephony equipment).

This option provides a much neater result than using separate filters at each extension. The possible downside is the extension wiring (now filtered) provides no ADSL signal, so you will need to connect your computer via the ADSL point at the Master Socket. This is fine if your computer is near to Master Socket. If not, you will need to have an ADSL 'unfiltered' extension fitted for hooking up the computer. If you are opting for an 'Engineer Install' system, the engineer will normally undertake this upon request, or s/he may be able to suggest a more suitable configuration.

If you are undertaking a 'Self-install' package, Fig.4 offers one possible scenario. As the wiring to each extension is left 'unfiltered', it will enable you to connect your computer to any of the extensions, but it does mean you will need to use a filter for each item of telephony equipment you use.

This option is likely to be the easiest to install and provides the most flexibility (since at each point there is a filtered and unfiltered connection). The downside is you may need to purchase a number of filters and depending on the type of filters used, the end result probably won't be as tidy as the Engineer Installed option.

Fig. 5 is another alternative for self-install and is almost a replication of the Engineer Installed option, but using a micro filter instead of adapting the Master Socket. You are not permitted to tamper with the BT Master Socket, but you are allowed to filter the signal after it leaves this socket.

The disadvantages are similar to those of the Engineer Installed option and you may need to install an ADSL unfiltered extension if your computer is not near to the Master Socket.

The above scenarios are not intended to cover all possible alternatives, but are used to represent the more likely cases. It may be that a combination of two or more of the scenarios would be better suited to your situation.