| 摘要 |
<p>Detector of signalling information, of the telephone metering type, emitted in the form of periodic pulses obtained from specified- frequency alternating signals which are transmitted in analogue form by way of a two-wire (A, B) line (2), in particular to an analogue network line junction of a private-type telephone installation.
<??>This detector comprises an input filter (4) centred on the frequency (Ft) of the expected signallings, a sampler (6) connected, on the one hand, to the output of the input filter (4) and, on the other hand, to the output of a clock (7) supplying a signal (HE) whose frequency (FE) is close to the value (Ft), a low-pass filter (8) within whose band the characteristic detection signal leaving the sampler is to be included, and a level detector (9) able to supply a presence signal in respect of a characteristic level signal greater than a predetermined threshold output by the low-pass filter (8).
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