| 摘要 |
PURPOSE:To detect assuredly that a PB signal is received with a proper level for a continuity test, etc. of a telephone exchange network, by dividing the output signals into groups of prescribed low and high frequencies. CONSTITUTION:An input circuit 1 consists of a transformer which performs the matching of impedance, the balanced-unbalanced conversion, etc. to a telephone circuit and an amplifier which is used when necessary. The input processing is carried out for the PB signals received by the circuit 1, and then these signals are distributed to band-pass filters 2L and 2H respectively. The filters 2L and 2H transmit only the PB signals of low and high group frequencies, and full wave rectifying circuits 3L and 3H rectify the transmitted signals of low and high group frequencies to obtain the absolute level of each input signal. A level detecting circuit 5 compares the absolute level of each input signal with the threshold voltage 4. When the absolute level is higher than the voltage 4, it is decided that the input signal levels of both low and high group frequencies are higher than the prescribed lower limit levels respectively. Then an output showing this information is transmitted to open an AND gate 8. |
