GB1212908A - Improvements in or relating to pulse code modulation transmission systems - Google Patents

Abstract

1,212,908. Testing pulse repeater stations. SIEMENS A.G. 20 Sept., 1968, No. 3785/69. Divided out of 1,212,907. Heading H4L. In a P.C.M. system means are provided for testing intermediate stations such as 8, from a terminal exchange 1. At the exchange, normal P.C.M. signals are modulated at 3 by a low frequency rectangular wave from a generator 2, the repetition frequency of the wave being adjustable to a different value for each intermediate station to be tested. The modulation takes place over several frames and is in the form of 100% amplitude modulation so that the output consists of blocks of pulses having an envelope curve defined by the rectangular waveform and whose frequency spectrum is disclosed symmetrically about the bit frequency or in the case of bipolar pulses, half the bit frequency. At the station 8 the incoming pulses are regenerated at 9 and transmitted to the receiving end. The regenerated pulses are also demodulated at 10 to recover the low frequency signal which corresponds, with the pass frequency of a bandpass filter 11 whose output is rectified to operate a relay switch 12. By this means the regenerated signal is fed back via the regenerator 13 for the opposite direction of transmission and at the exchange 1 is supplied via a comparator 4 controlled by the normal synchronizing equipment to a fault indicating instrument 5. In a modification, the test signal is transmitted on by a relay-operated switch to a further terminal exchange for processing. It may be arranged that the synchronizing signals are unaffected by the rectangular wave modulation.