| 摘要 |
storing a phone number to prevent call without permission in a registered number recorder(5); converting the composite frequency signal transmitted through a telephone line into the digital signal, with a composite frequency decoder(2); decoding the phone number dialing transmitted through the telephone line by recognition of a central controller(1); and blocking the call by opening the telephone line for a constant time at a mode switch(8) when the decoded number coincides with the stored number.
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