1369062 Testing unattended repeaters SOC ITALIANA TELECOMUNICAZIONI SIEMENS SpA 12 Oct 1971 [29 Jan 1971] 47418/71 Heading H4R In a fault location system for a two way PCM link over a number of repeater stations an interrogation pattern is transmitted from one terminal station, and detected at the other terminal to effect connection between the incoming and outgoing lines at that station. At each repeater station an efficiency detector responds to a particular respective interrogation pattern to generate a signal representative of the operational state of the detector. As described the system comprises a number of outgoing A-B lines 1 to m/2 and a number of incoming, B-A, lines m/2 to m. Fortesting, an interrogation signal having a characteristic pulse pattern with a low frequency component dependent on the particular repeater station it is desired to test, is coupled to the outgoing line at station A from generator G. At the other terminal station B the pulse pattern is detected and used to effect connection between the respective outgoing and incoming lines so that the interrogation pattern is returned to terminal station A. At each station the outputs from the amplifiers of each direction of transmission are fed to respective inputs of the filter system, shown in Fig. 3. The signals are fed via limiters L1j and L2j to diode gates d1J and d2J one or the other of which is blocked by the particular polarity of the voltage applied to the supervisory line α. The signal from the amplifier for the particular direction of transmission being tested feeds through the other gate, passes through the filter Fj to be fed over the supervisory line α to the testing terminal station as an indication of the operative state of that repeater. By reversing the potential across the line α the amplifier for the other direction of transmission is tested.