| 摘要 |
The telephone subscriber filter has a blocking filter (5; 5') which keeps the charge pulses which arrive via the exchange line with frequencies in the vicinity of the upper voice band limit, preferably around 4 kHz, away from the telephone device and which comprises a reactance filter in the form of a chain circuit with the structure of an impedance-balanced filter; it is, however, designed on the telephone device (2) side for a complex termination comprising an 800-1000 OMEGA ohmic resistor (R2) and a 30-50 nF capacitor (C2) connected in parallel with it and on the exchange side for a real termination with a 1000-1200 OMEGA ohmic resistor (R1). A frequency converter (9) is connected downstream of the charge pulse receiving circuit (6') which converts the charge pulse frequencies into a frequency of 12 or 16 kHz which is suitable for conventional high-frequency metering and whose output on the blocking filter (5') side facing the telephone device (2) is coupled with the speech wires. <IMAGE> |
