Patent GB-1164369-A (GB)
Title: A Selective Calling Method and Device.
IPC: H04W88/02
Filed: 1967-11-02
Abstract: 1,164,369. Electric selective signalling. C.I.T.-COMPAGNIE INDUSTRIELLE DES TELECOMMUNICATIONS. 2 Nov., 1967 [5 Nov., 1966], No. 49885/67. Heading G4H. [Also in Division H4] In a selective calling system featuring calling codes made up of one or more trains of regularly spaced pulses, the receiver at a station includes a comparison element A, Fig. 2, which comprises a numerical pulse divider 8, and a delay circuit 7, both of which are characteristic of the station, and which have their input sides connected to each other and to means feeding code pulses received, and their output sides connected to the respective inputs of a coincidence gate 10. When the appropriate calling code is received the delayed pulses begin to emerge from the circuit 7 as the divider 8 gives an output, and the gate 10 conducts. A train of pulses comprises an initial long pulse D, Fig. 1, a number of shorter code pulses #, and a final pulse S. The pulse S has a duration which is intermediate the durations of the pulses D, #, and as described it is associated with the pulses # in the numerical code. Pulses derived by an input unit 2, Fig. 2, from a signal input at a terminal 1, are connected both directly, and through a pulse duration selector 3 and a monostable circuit 4 to the respective inputs of an AND gate 5. The selector 3 is set to the duration D and when the initial pulse arrives it operates the monostable circuit 4, which provides a first input to the gate 5 while the remaining pulses arrive, and which when it restores re-sets the divider 8 by means of a connection 14. The output of the gate 5 is connected to the inputs of the delay circuit 7 and the divider 8 and also, through a pulse duration selector 9 which is set to a duration S, to one input of an AND gate 12. The output from the gate 10 is connected through a delay circuit 11, which has a duration of S - #, to the other input of the gate 12. Thus, output from the selector 9 following arrival of the final pulse S will coincide with delayed output from the gate 10 at the gate 12, which then provides output at a terminal 13. In another embodiment, a pulse train comprises an initial pulse (D), Fig. 3 (not shown), and three sub-trains of pulses (#), each terminated by a pulse (S) which is not included in the numerical code. A monostable circuit 4, Fig. 4, which is operated by the arrival of the pulse (D), holds for the whole duration of the pulse train. Output from an AND gate 5 is connected to an (S) pulse duration selector 9, to a first comparison element A1, and to one input each of AND gates 18, 21. The (S) pulse duration selector 9 is connected to an (S) pulse counter 15 which provides outputs in sequence to respective first inputs of AND gates 16, 19, 23. The first sub-train of pulses (#) and the first pulse (S) result in output from the gate 16, which operates a switching circuit 17 to energize the other input of the gate 18. The second subtrain of pulses (#) results in output from the gate 18 to a second comparison element A2, and the second pulse (S) results in output from the gate 19, which operates a switching circuit 20 to energize the other input of the gate 21. The third sub-train of pulses (#) results in output from the gate 21 to a third comparison element A3, and the third pulse (S) results in output from the gate 23 to a terminal 24.