| 摘要 |
<p>To permit address-free fault location on digital communication paths with several intermediate repeaters, one or more identification signals must be recognized in the intermediate repeaters with sufficient certainty. The identification signals are digital signals with periodically recurring sections which are marked with a string of successive like bits (e.g., 0 bits) and have different durations for a first identification signal and a second identification signal. The circuit contains a time discriminator (1) which responds when a string of successively received like bits is characteristic of a section of an identification signal. It then provides a pulse equal in length to this section to a frequency discriminator (2) which responds when such pulses recur at a frequency characteristic of an identification signal. The frequency discriminator thus delivers an output voltage whose amplitude is typical of one identification signal or the other because of the different pulse durations. By comparing this voltage with reference voltages, a following comparator (3) derives control signals indicating the reception of the respective identification signal.</p> |
