| 摘要 |
PCT No. PCT/US93/09047 Sec. 371 Date May 23, 1994 Sec. 102(e) Date May 23, 1994 PCT Filed Sep. 27, 1993 PCT Pub. No. WO94/08417 PCT Pub. Date Apr. 14, 1994A Radio Frequency Interference Filter (10, 12) is connectable in series in the tip (T) and ring (R) branches of a telephone circuit. A first suppression stage (20) has a first inductor (L1) connectable to the tip (T) branch of the circuit and a second inductor (L2) connectable to the ring (R) branch of the circuit. The second suppression stage (22) of one embodiment of the filter (10) has a transformer (T1) with one winding (W1) connected in series with the first inductor (L1) for the tip (T) branch of circuitry and the second winding (W2) connected in series with the second inductor (L2) for the ring (R) branch of circuitry. In a second, alternative embodiment of the filter 12, the second suppression stage (22) has one ferrite-core inductor (L3) connected in series with the first inductor (L1) for the tip (T) branch of circuitry and a second ferrite-core inductor (L4) connected in series with the second inductor (L2) for the ring (R) branch of circuitry. A fuse (F1, F2) may precede each inductor (L1, L2) to protect the filter (10). The filter (10, 12) may be encapsulated to provide protection from adverse environmental changes.
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