Apparatus for coupling signals to or from a two-wire line.

摘要

A filter comprising reactive components (22 to 27) which define pass and stop bands has the impedances of the components selected to minimize the sum ¦Zin-Z2 + ¦Zout- Z1¦ in the pass band, where Zin and Zout are respectively the input and output impedances of the filter and Z1 and Z2 are nominal termination impedances at respectively the input and output of the filter. The design is exemplified by a 5th order low pass filter for coupling voice-band signals to a telephone subscriber line to which above voice-band signals are also coupled via a transformer (33). A parallel resonant circuit (39, 39), which has a low impedance in the voice-band, is connected in parallel with a winding (34) of the transformer (33) to prevent degradation of the filter characteristics in the voice-band.