Bandstop filter for e.g. intercom system - has current compensating inductor and resonant circuit for preventing HF signals passing to rest of household mains supply network

摘要

The filter has a current-compensating inductor with two coil halves wound in the same sense on a closed ferrite core. The windings (2,3) of both coil halves are connected to a centre tapping (4,5) by a capacitor (6). The windings and capacitor are tuned to a resonant frequency. The second capacitor (7) and second coil (8) form a resonant circuit connected between the mains-side connection (9) of the winding and the neutral conductor. The second coil is a tuning coil. The filter's casing consists of two parts (21,21') with recesses and holes etc. for the components. A central recess (22) holds the current-compensating inductor in one part of the casing. Lateral recesses (26) hold the circuit board (25) carrying the second capacitor, second coil and connection terminal.