Patent GB-876752-A (GB)
IPC: H04W84/02
Abstract: 876,752. Radio signalling. WESTERN ELECTRIC CO. Inc. Dec. 2, 1959 [Dec. 12, 1958], No. 40902/59. Addition to 793,991. Class 40(5) In a system of the type described in the parent Specification, providing two-way radio telephone communication between any one of a number of dispatchers' stations and units of a mobile fleet individual to that dispatcher's station, via a control station, and in which "calls waiting" are registered in a sequence circuit at the control station, additional facilities are provided whereby mobile units other than those of a mobile fleet associated with a dispatcher, defined as urban mobile units, may be interconnected via the control station with a dial telephone exchange. Means at the control station exclude the telephone exchange from access to the radio transmitter when a dispatcher's station is connected, and exclude the dispatchers' stations when the exchange is connected. As shown, conductors R5, T5 and R1, T1, represent terminations in telephone circuits assigned to dispatchers No. 5 and No. 1 respectively, there being five dispatchers, each dispatcher having an individual channel control circuit such as that shown in Fig. 2 associated with conductors R5, T5, and Fig. 5 associated with R1, Tl. Conductors R o  T o , indicate a connection to the two-way operator's trunk circuit at the exchange. The common equipment comprises a system control circuit shown in Figs. 7, 8, 9, and a circuit extends from the common equipment to the radio transmitter via conductors T T , R T , Fig. 6, and to the radio receiver via conductors T R , R R . A telephone 3-03 and associated circuit, Fig. 3, is used for testing and monitoring. Each dispatcher has a corresponding tone generator Fig. 1 or 4, for modulating the transmitted carrier to call his particular fleet and each fleet of mobile units transmits on a common carrier modulated with a distinctive frequency to call the corresponding dispatcher by operating a tone operated switch, Fig. 1 or 4. Outgoing call by dispatcher-system idle. Initiation of a call by say Dispatcher No. 5 energizes relay 2-L5 which is followed by relays 2-LA5 and 9-TOA. Operation of relay 2-LA5 connects a meter 2-16, which measures the time the dispatcher is connected to the system, to an A.C. source, energizes a recorder 9-03, which provides a printed time-of-day record, and energizes relays 2-P5 and 1-LB5. Relay 2-P5 is followed by relay 9-BL which starts the recorder, and 2-C5, which provides an alternative circuit for relay 1-LB5. Relay 9-BL also switches on a "transmitter busy" lamp, Fig. 9, and switches on the transmitter via repeating coil T and a remote relay (not shown). Relay 9-BL is followed by relay 9D which causes relay 9-CI to pick up to prepare a circuit for interrupting the transmitted carrier. Relay 9-TOA locks and is followed by slow-release relays 9-TOB and 9-TOC which determine the time for which the calling tone is transmitted. Relay 9-TOC is followed by relay 8-TOS which in conjuction with operated relay 1-LB5 connects the tone generator. 1-T9, Fig. 1, to the transmitting amplifier 6-TA, Fig. 6. Operation of relay 1-LB5 also connects the dispatcher's line circuit T5, R5, to the radio stations via transformer D5. Relay 8A picks up when relay 2-P5 operates and is followed by relay 8-RVT and slow-release relay 8-B and all the RV relays except relay 2-RV5 associated with the calling dispatcher operate. Operation of the RV relays applies a "busy tone" source, Fig. 8, via repeating coils D1 &c. to all dispatchers' lines other than the calling dispatcher. Relay 8-RVT operates to apply the busy tone to the two-way operator's circuit. When the transmitter is radiating conductor T is earthed and relay 6-SS operates via lamp S thus releasing relays 9-TOA, 9-TOB, 9-TOC, and 8-TOS to disconnect the tone generator. The selectors in the fleet of mobile units individual to the calling dispatcher open squelch units in response to the tone modulation to remove muting. The dispatcher designates the required unit by voice and the mobile unit answers by removing the handset and momentarily operating a push-to-talk button to transmit a burst of carrier. This operates a relay (not shown) at the control station receiver whereby relay 6-COD operates and is followed by relay 9-E, thus releasing slow-release relay 9-D and slow-release relay 9-CI. This interrupts the transmitted carrier for a time sufficient to disable all the mobile receivers except the one answering the call. At the conclusion of the call the mobile unit push-to-talk button is released to release relay 6-COD. The dispatcher replaces his handset and relay 2-L5 is released thus releasing the remaining relays and removing the busy tone from the other dispatchers' lines. Incoming call from a dispatcher mobile unitsystem idle. Mobile units can complete calls only when the system is not in use but may register "calls waiting" during an "enforced waiting" period, when the system is idle. When the system is idle the "Tone switches", Figs. I and 4, are bridged across the line to the radio receiver and conditioned to respond to the incoming signals via transformer TR. A dispatcher mobile unit originates a call by transmitting a burst of carrier modulated with the channel identification tone which operates relay 6-COD and 9-E as before but they have no function in this case. The incoming tone actuates say relay 1-K5 associated with the tone switch, Fig. 1, which is followed by relay 2-MR5. Relay 2-P5 operates and is followed by relay 8-A and relays 8-B, 8-RVT, and all RV relays associated with other dispatchers are energized. Relay 2-C5 operates and locks relay 2-MR5 through the key 8-09 and operates relay 1-R5 followed by relays 9-BL as previously described to switch on the carrier, and relay 8-TOS. A ringing signal having a one second ringing interval followed by a one second silent interval to ring the dispatcher's bell is obtained from the relay combination 9-SA, 9-SB, 9-SC, in combination with an interrupter 8-04 and AC-DC ringing generator 7-02. During each ringing interval a D.C. pulse operates relay 7-RG to connect the "low-tone" equipment 6-LT, Fig. 6, to the radio transmitter to indicate to the calling mobile unit that the dispatcher's line is being rung. A relay 1-T P5 operates when the call is answered, and releases relay 1-R5 to disconnect the ringing circuit. Relays 9-BL and 6-SS are released and relay 2L operates. The system then operates as when a dispatcher is calling with the exception that relay 9-TOA is not operated since it is not necessary to transmit the identification tone. Outgoing call to urban unit originated by traffic operator-system idle. When the operator "plugs in" relay 3-CA is operated via conductors T o , R o , and is followed by relays 9-CC, 9-CE, and 9-CB, which reverses the connections of T o , R o  in known manner to prevent dial pulse transmission. Relay 9-CH operates and is followed by relays 8-PT and 9-CK. Relay 8-PT is followed by relays 8-CT, 8-A, 8-B, and this relay combination determines the sequence in which waiting calls are registered. Relay 8-A operates the RV relays associated with the dispatchers' control circuits to bridge a busy tone on all dispatchers' lines as previously described. Relay 8-CT operated completes the circuit of relay 7-MD which disables the tone switches, operates relay 7-CF which connects conductors T, R, to the repeating coil OT and activates the recorder 9-03, and operates relay 9-BL to switch on the transmitter carrier, whereupon relay 6-SS operates. Relay 9-CK operated energizes relays 9-CL and 9-CM, followed by 9-CP and 9-CR. The urban mobile units respond to alternate bursts of 600 and 1500 c/s. tones from the selective signalling oscillator, Fig. 6, and before transmitting dialling pulses similar bursts are sent to ensure that selectors in all the urban mobile units are in a released condition. Relays 9-CK and 8-CT operated energize relay 6-PD which is followed by slow-release relay 6-SR. Relay 6-DS operates and applies 600 c/s tone across the repeating coil T. With relays 6-SS, 8-CT, and 9-CR operated, relay 9-CJ operates and releases 9-CK which in turn releases relays 6-PD and 9-CL. The release of relay 6-PD operates relay 6-SW which applies the 1500 c/s. tone across transformer T, and de-energizes relay 6-SR but it does not have sufficient time to release. The release of relay 9-CK also releases slow-release relay 9-CL to re-energize relay 6-PD followed by 6-SR and 6-PD2. The release of relay 9-CL releases relays 9-CM, 9-CP, and 9-CB which restores the connection of conductors R o , To, to normal to give the operator a "start dial" signal and provides an alternative path for relay 6-PD. Each dialling call consists of four digits totalling 23 or 25 pulses beginning and ending with 600 c/s. Upon the completion of the dialling cycle a delay of 4À5 seconds is provided to permit call indicators in the mobile units to operate. A final tone of 1500 c/s. is sent to clear the mobile unit selectors and turn off the call indicator after which the signalling oscillator is disabled and conductors R, T, connected via transformer T to the radio transmitter. The first dialling pulse releases relays 3-CA, 9-CC, and 6-PD and relay 9-CO operates and locks. At the end of each dial pulse relays 3-CA, 9-CC, operate and are followed by 6-PD, and a capacitor 7-14 in the timing circuit of tube V4 starts charging and at the beginning of each dial pulse relays 3-CA and 9-CC release to discharge the capacitor via resistor R1 6 and cause re-cycling of the timing circuit. The release of relay 6-PD at the start of each oddnumbered dialling pulse energizes relay 6-PD3 via a winding of relay 6-PD2 and relay 6-SW is released to apply the 600 c/s. tone to the transmitter and the operation of relay 6-PD at the end of the dialling pulse terminates the 600 c/s. tone transmission. In response to the start of each even-numbered dialling pulse, relay 6-