ARRANGEMENT FOR ADJUSTING AN ADAPTIVE DIGITAL BALANCE FILTER INCLUDED IN A SUBSCRIBER UNIT

摘要

An arrangement for adjusting an adaptive digital balance filter (B) included in a subscriber unit (I) connected to a telephone line contains a selection unit (III), which can be connected to the subscriber unit either via the exchange or via a separately arranged switch (K). When the selection unit (III) is connected to the subscriber unit (I), the balance filter (B) is disconnected from both branches of the subscriber unit (1). A test signal generator (TS) is included in the selector unit (111) for sending a signal on the lines via both branches of the subscriber unit (1). There is further included a plurality (N) of digital filters (B1... BN) where the transfer function of any of the filters (B1... BN) closely coincides with the transfer function of the filter formed by the line impedance and the portion of the subscriber unit (I) which is connected to the line and to the balance filter (B). By means of a measuring unit (M) there is formed a criterion for determining which one of the filters (B1... BN) included in the selector unit (III) most closely matches the above-mentioned filter, and the parameters of the selected filter (Bk) are allowed to determine the parameters of the balance filter (B).