Once ADSL is installed the line will be transmitting data on another frequency from the exchange, this frequency can be picked up by a telephone and cause hissing on the line.
 A microfilter filters the broadband frequency out and also gives you an extra port to plug your ADSL hardware into as it will not connect directly to your phone socket.
Any telephone socket in your house or business will need to have one of these filters on it (unless no equipment is connected )and the placement is vital to the operation of the ADSL, see the diagram below for instructions on placing the filter correctly.

MOST COMMON MISTAKE.
Your broadband is connected in another room from your master socket
1)this is run on an extension cable so is then filters at the wrong point
2)as it is run as an extension you have now fitted 2 x filters on the same line
3)you have used an extension lead but not an adsl lead so you are unable to filter correctly .

 It is not recommended to use a telephone extension cable as it is not designed to handle digital signals. If your computer is too far away from your phone socket you will need to purchase a RJ11 cable which is designed to transmit high quality digital Broadband signals. Longer RJ11 cables are available

TEL SOCKET

TEL SOCKET

ADSL FILTER

ADSL FILTER

STEPS HOW TO CORRECTLY CONNECT
 YOUR ROUTER TO THE PHONE LINE

 MODEM  / ROUTER