GB1346257A - Telecommunications systems - Google Patents

Abstract

1346257 Transmission systems SIEMENS AG 3 Sept 1971 [4 Sept 1970] 41159/71 Heading H4R In a telecommunications system in which a receiver at one station can be switched over from a presently operational disturbed channel to another channel, with the operational channel malfunction indicated by non reception of a pilot tone transmitted thereon, a pilot generator is provided at the one station and transmits over a return channel a signal whose frequency or frequencies indicate the operational state of the available channels. As described data is fed in parallel to the inputs of two channels A and B from a transmitter 11 at a terminal station I. A pilot signal, from generator 15, is also fed to the two channels and, at a terminal station II, pilot receivers PA and PB are arranged to detect the pilots on the two channels and effect switch over from a faulty channel to a working channel in a manner as described in Specification 40504/71. The failure of one of the channels A or B is immediately detected by the respective pilot receiver PA or PB and causes the deenergization of the normal pilot generator 15 for the return path and the energization of one or the other or both the generators 16 and 17, depending on whether channel A, channel B, or both channels A and B, are faulty, the generators 15, 16 and 17 being respectively of 300, 320, and 340 Hz. At the terminal station I pilot receivers are provided for all the possible pilot frequencies on both incoming channels and a logic circuit 31, in response to the selective energization of the pilot receivers by the incoming signals lights one or more of the lamps 321 to 325 indicating the functional state of all the outgoing and incoming channels. Each pilot receiver includes a circuit which detects noise in the incoming signal and which blocks the receiver to cause change over to a substitute line if the noise level exceeds a predetermined value.