| 摘要 |
PURPOSE:To obtain a master-subordinate system interphone which allows a secret talk even when respective subordinate equipments are of exactly the same constitution by employing the same frequency f1 for transmission from a master equipment to each subordinate equipment and also using the same frequency f2 for transmission from each subordinate equipment to the master equipment. CONSTITUTION:A hook signal goes up to a level H by the off-hook operation of the mater equipment 4 to put a tone oscillation circuit in operation, and an FF 36 closes an analog switch 24 by the H-level signal to operate a transmitting circuit 20. When the name of a specified slave equipment is called through a microphone 14, a modulated carrier f1 is transmitted to respective slave equipments 6. The receiving circuit 64 of each subordinate equipments demodulates the carrier, the output of a tone detecting circuit 68 goes up to H, and an FF 74 is set to close an analog switch 65, voicing the name of the subordinate equipment. The hook signal goes up to H by the off-hook of the subordinate equiment and a modulated carrier f2 is transmitted to the master equipment. The output of the detecting circuit 30 of the master equipment goes up to H and the oscillating circuit 19 stops. Output of detecting circuits of other 68 subordinate equipments go down to L by the ceasing of tone signals and switches 65 are opened. The switch 65 of the specified subordinate equipment, on the other hand, is held closed. |
