GB1407088A - Telecommunication systems - Google Patents

Abstract

1407088 Radio signalling SIEMENS AG 29 Sept 1972 [22 Oct 1971] 45013/72 Heading H4L A multichannel telecommunication system is provided with means for automatically switching over to a spare channel in the event of a fault in a radio link. As shown in Fig. 1, a radio relay system is provided with operational channels I to IV and two substitute channels. A filter W feeds six radio receivers ME whose outputs a1 to a6 are connected via receiving switching network NE to a transmitting switching network NS whose outputs c1 to c6 are connected via respective transmitters MS and common filter W to a transmitting aerial. The remaining relay stations are connected similarly and may include transmission line sections, the return path being identical. Four supervisory channels are provided for transmitting back to the transmitter of a link such as SA2 information regarding the condition of the respective channels I to IV and controlling the changeover to a spare channel. These signals may be transmitted via the return link or by a special line or radio link. Each supervisory channel has a transmitter KS which may be switched to transmit one of three frequencies to an associated receiver KE under the control of receiving network NE to denote that operation is normal or to denote which of the two spare channels is to be utilized. Each transmitter KS1, Fig. 2, comprises an oscillator 4 which normally operates at frequency f 0 (system normal) or may be switched via line 1 or line 2 to frequencies f 1 or f 2 respectively. The output of the oscillator is filtered at 5 and supplied via a filter 6 in the receiver KE1, amplifier 7 and limiter 8 to a frequency discriminator 9 whose two amplitude maxima coincide with frequencies f 1 and f 2 which lie symmetrically above and below f 0 . Frequencies f 1 or f 2 produce a response in circuits 10 or 11 respectively which is used to effect the required switching. A circuit 12 produces a further signal at terminal 3 when either f 1 , f 2 or f 0 is present whereby in the absence of f 1 or f 2 the circuit is monitored. If a fault causes the signal at terminal 3 to be outside the normal range it may be arranged to maintain the switching state existing before the fault.