This is a small adaptor that plugs into your phone line, allowing information to be split and filtered between VOICE and DATA. Using this allows an ADSL broadband Internet connection and voice line to run / be used at the same time from one phone socket.
Microfilters are often also referred to as Splitters and any home with a DSL (ADSL) based broadband connection should ideally install such a device on each phone line extension for the related telephone line (i.e. connect them into the wall box where you connect your phone) to avoid interference problems.
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> Splitter