| 摘要 |
A signal transmission control apparatus connected between a telephone line and a terminal device controls signal transmission therebetween in no-ringing service. First DC and AC circuits of the apparatus become conductive in response to a DC control voltage from the telephone line. The first DC and AC circuits are connected to the telephone lines and the leads of a primary coil of the transformer of the apparatus. The secondary coil of the transformer is connected to the terminal device and an amplifier and first detection device of the apparatus. A subsequent AC calling signal from the telephone line, received on the first AC circuit, effects conduction in second DC and AC circuits through serial operation of the first detection circuit, a control circuit, a switching transistor and closure of relay contacts. The second DC and AC circuits are of lower resistance and impedance, respectively, than the first DC and AC circuits, respectively to indicate operation of the apparatus to the telephone line and minimially to affect signal transmission of AC information through the transformer primary and secondary coils.
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