| 摘要 |
A call barring device for a telephone terminal connected to the telephone network and operating according to a multi-frequency dialling procedure can be manually activated and de-activated. When it is activated, dialling signals are suppressed, whereas incoming calls are allowed through. To enable the call barring device also to be used independently of the terminal, a low-pass filter, which is normally enabled, is inserted into the connection line. Furthermore, a ringing signal receiving circuit, which, when activated, supplies an auxiliary current, is connected to the connection line. In addition, a main power supply is also provided which can be activated when the terminal is seized and which is connected to the connection lines. Both the main and auxiliary power supplies and the ringing signal receiving device are connected to a disablement device which disables the low-pass filter only when either the ringing signal receiving device responds or the main power supply is subsequently activated.
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