Patent GB-1396600-A (GB)
Title: Selective signalling apparatus with storage of call signals
IPC: H04W88/18
Filed: 1972-11-28
Abstract: 1396600 Radio signalling MOTOROLA Inc 28 Nov 1972 [6 Dec 1971] 54914/72 Heading H4L In a radio paging system, e.g. for hospitals, the receivers are provided with means for storing a call so that if it is inconvenient to receive a call on a particular receiver it can be determined later if a call has been made on that receiver. As shown in Fig. 1, audio signals from the receiver 12 are amplified (18, 20, 22), and supplied to an audio transducer 24, the energization of the amplifiers being controlled by a regulator 28 and OR gate 30. As described, the selective code is tone A followed by tone B, which are selected by filters 34, 36 respectively and supplied to decoder 35. The reception of tone A for a predetermined time causes detector 38 to discharge capacitor 39 and at the termination of the tone the capacitor 39 recharges to trigger the inverter 42 and rapidly discharge capacitor 43. This provides a low input to inverters 45 until capacitors 43, 44 are charged via resistor 41. The low input to inverter 45 provides a high input to AND gate 46 which is delayed by the charge of capacitor 39 and the discharge of capacitor 43. Detector 48 responds similarly to tone B to discharge capacitor 49 whereby inverter 52 supplies a high input via OR gate 54 to the AND gate 46. The output of gate 46 is supplied via resistor 58 and OR gate 30 to turn on the regulator 28 so that the audio amplifier is operative and is also supplied via inverter 57 to the input of inverter 45 so that the AND gate 46 maintains an output so long as tone B is present. The output of gate 46 is also applied to an astable circuit 60 and AND gate 64 which also receives the output of circuit 60, whereby tone oscillator 66 is activated intermittently to supply signals to audio amplifier stage 20, which are reproduced at 24. When the pager is for use with tone only, the output of gate 46 is also applied via RC circuit 70, 71 and OR gate 54 to the input of gate 46 to enable the tone oscillator to operate for an additional time after the tone B ceases. The memory circuit 75 is coupled to the audio amplifier 18 and the output of gate 46 by a switch 78. When the switch is closed and the decoder provides an output, transistor 80 maintains the audio amplifier disabled. An input is supplied to AND gate 82 which receives a second input from inverter 84, the output of gate 82 being supplied via OR gate 54 to maintain the output from gate 46. The switch 78 is also connected to one input of AND gate 86 which receives its other input from the positive terminal 26 in the audio amplifier. The output of gate 86 is supplied via delay 88 to render transistor 90 conductive to supply a second delayed input to gate 46 to hold it operated for a period of time after the input on conductor 69 ceases. A reset switch 95 when operated causes transistor 96 to conduct so that the output of inverter 99 via OR gate 30 actuates the regulator 28 to energize the audio amplifier and reproduce the tone from oscillator 66 if a call has been received. Also one input to gate 86 falls and removes the input to delay 88 and the inverter 87 resets the delay so that transistor 90 becomes non-conducting to unlatch the decoder 35. When switch 95 is released, transistor 96 becomes non-conducting and monostable 100 is triggered which via inverter 84 removes the second input to gate 82 to remove the clamp potential from gate 46 whereby the audio amplifier is de-energized. The stored call may also be reproduced by opening the switch 78. In tone and voice pagers, switch 102 is used instead of switch 95.