Sensor for detecting the traffic of information streams consisting of analogue signals on telecommunication lines

摘要

A sensor as is known from German Offenlegungsschrift 3017623 is supplemented here in such a manner that it evaluates characteristic interference signals in addition to evaluating the signals occurring within the spectral range of the useful signals. For this purpose, a low-pass filter 6 with a cut-off frequency of 300 Hz is connected in parallel on the input side with the band pass filter 3 for the useful signal range from 300 to 3,400 Hz. Its mean output voltage is compared with the mean value of the useful signals. Only when the mean value of the useful signals supplied by the integrator 7 is higher by a factor adjustable by the voltage divider 9 than the mean value of low-frequency interference signals picked up at the integrator 8, does a comparator 10 output an output signal which permits detection. A corresponding arrangement with band pass filter 11, integrator 12, voltage divider 13 and comparator 14 evaluates the frequency range of audio tones around 460 Hz. To determine whether voltages of zero frequency are present on the speech wires a, b at an amplitude which causes the stray pickup of strong interference, amplifiers 15, 16 pick up these voltages separately. Comparators 17, 18 compare them with a reference voltage. The signal detection is allowed or blocked depending on the result of the comparison. <IMAGE>