AV:Link ADSL Signal Filter - BT431A to RJ11 & BT431A

The AV:Link ADSL signal filter is a white plastic adapter that converts a single BT431A telephone plug into two outputs: one RJ11 socket for ADSL broadband connection and one filtered BT431A socket for a telephone or fax machine. The internal filter separates the high-frequency ADSL signal from the voice-frequency telephone signal, preventing interference between the two devices when both share the same phone line.

Designed for UK residential and small office installations where ADSL broadband and a landline telephone connect to the same wall socket, the filter plugs directly into the BT431A master socket or extension and requires no tools or wiring. The ADSL modem or router connects to the RJ11 socket, while the telephone or fax connects to the filtered BT431A socket. Up to four filters can be used on a single telephone line if multiple extension points need filtering, though most installations only require one filter at the master socket.

The filter weighs 25g and measures approximately 60mm x 40mm x 25mm, so it sits flush against the wall socket without obstructing adjacent sockets or furniture. The white plastic casing matches standard UK telephone wall plates and the design includes no LEDs or moving parts, making it a passive, maintenance-free component once installed.

Why is an ADSL filter needed?

ADSL broadband and telephone voice signals share the same copper line but use different frequency ranges. Without a filter, the ADSL signal can cause crackling, static or interference on the telephone line, and the telephone signal can disrupt the broadband connection. The filter separates the two signals so each device receives only the frequencies it needs.

Where should the filter be installed?

The filter plugs directly into the BT431A wall socket where the ADSL modem or router would normally connect. If you have multiple telephone extension sockets in the property and use phones on those extensions, each extension socket may need its own filter to prevent interference. Most users only need one filter at the master socket.

Can multiple filters be used on one line?

Yes. Up to four ADSL filters can be used on a single telephone line if you have multiple extension points. Each extension socket with a connected telephone or fax should have its own filter to prevent the telephone device from interfering with the ADSL signal.

Is this compatible with fibre broadband?

No. This filter is designed for ADSL (Asymmetric Digital Subscriber Line) broadband, which runs over traditional copper telephone lines. If your broadband is delivered via fibre-to-the-cabinet (FTTC) or fibre-to-the-premises (FTTP), you typically do not need an ADSL filter as the broadband signal does not share the voice line in the same way.