Patent GB-973733-A (GB)
Title: Automatic monitoring in telecommunication systems
IPC: H04B1/74
Filed: 1960-12-30
Abstract: 973,733. Radio signalling. WESTERN ELECTRIC CO. Inc. Dec. 30, 1960 [Jan. 4, 1960], No. 44702/60. Heading H4L. A multi-channel communication system is provided with means for detecting a faulty channel and substituting any one of a plurality of spare channels. The system described has six working channels and two spare (protection) channels and includes a radio transmitting terminal, one or more repeaters, and a radioreceiving terminal an auxiliary circuit being provided for effecting switching to the spare channels. Signals on working channel 1, for example, are passed via a channel monitor 10 and transmitter switch 20 to a radio transmitter 40 where they are converted from an intermediate frequency to a transmitting frequency. At the repeater the signal is received by a receiver 50 and converted to the intermediate frequency, passed through a channel monitor 60 and re-radiated after heterodyning to a transmitting frequency at 70, Similarly, at the receiver terminal the signal is received at 80, monitored at 90, and passed via the receiver switch 120 to the utilization point. The channel monitors comprise transistors biased to conduct by the rectified signal, which are cut-off when the signal falls below a predetermined level. In order to check the spare channels when idle a monitoring signal is supplied to them from carrier supply 150 which is absorbed under this condition in load resistors 170. In the auxiliary circuit a tone generator 700 at the receiver terminal sends a tone for each channel via reporter circuits 800 to a separator and converter 600 at the transmitter terminal when the channels are in order. The auxiliary circuit elements may be coupled by a radio or line circuit. The separator 600 filters out the various tones and converts them to D.C. for application to the transmitter switch control 200. When a channel is not functioning correctly the corresponding channel monitor releases a relay and prevents the monitoring tone from being transmitted to the separator 600. The transmitter switch control 200 also receives a signal from the channel monitors 10 at the transmitter terminal giving an indication if the failure is due to a fault in a previous section. If the fault is in the section shown a signal is sent from the transmitter switch control 200 to the transmitter switch 20 which affects a bridging switch from the failed working channel to a selected spare channel. Also the transmitter switch control sends a signal, which is converted from D.C. to the appropriate tone by converter 500, to the receiver switch control 400 which supplies a signal to the receiver switch 120 to cause a transfer from the faulty working channel to the selected spare channel. Normally the spare channel 7 serves channels 1 to 3 before channels 4 to 6 and the spare channel 8 serves channels 4 to 6 before channels 1 to 3. In the event of the failure of one of the spare channels, the other becomes available as a replacement for any of the working channels. Also, if one of the spare channels has been taken into use, the other becomes available for any of the remaining working channels. The Specification includes circuit diagrams including logic circuits for effecting the various switching operations and the switching sequences for various operating conditions are tabulated.