Patent GB-1321050-A (GB)
Title: Communication receiver
IPC: H04B1/16
Filed: 1970-09-21
Abstract: 1321050 Transistor circuits; radio signalling K H WYCOFF 21 Sept 1970 [29 Sept 1969] 44927/70 Headings H3T and H4L In order to obtain reduced power consumption from the direct current supply to a radio receiver in the absence of a signal, the supply is pulsed, being held steady on receipt of the appropriate signal in response to a tone modulated on the signal carrier and characteristic of the signal. One embodiment comprises an F.M. receiver in which a single calling tone is used. The discriminator 41, Fig. 2 feeds audio amplifier 160, Fig. 3, via lead 42 and also a decoder 50, Fig. 2. In decoder 50 the audio modulation is amplified in amplifier 51 and applied to a tuned filter 54, 55, 56, 71 selecting the control tone for application to a voltage-doubler rectifier 72, 73. The complete audio modulation is rectified by a voltage-doubler rectifier 62, 63, the output from which is utilized to bias back the rectifier system 72, 73 and so block it in the absence of the control tone. The presence of control tone renders transistor 81 conductive, whereby control transistors 91, 106 normally non-conductive, are rendered fully conductive so that control lines 96, 108 respectively receive positive biases. A stable multivibrator: pulser, circuit 120.- Transistors 122, 125 are back-coupled over capacitors 126, 129 and diodes 124, 128 to produce a train of narrow pulses, which are amplified by D.C. amplifier 131, 134 and applied over line 136 to intermittently energize the preliminary stages 30 of the receiver. When line 96 is positively biased, however, transistor 131 is held conductive so that transistor 134 is conductive and applies a continuous energizing potential to the line 136. Timer circuit 140 takes the form of transistors 141, 145 backcoupled as a monostable circuit, transistor 141 being normally biased non-conductive so that current does not flow in resistor 146 and transistor 145 is consequent non-conductive: no potential is then applied to the line 150, so that the audio amplifier 160 is cut off. When line 108 goes positive, however, transistor 141 becomes conductive, rendering transistor 145 conductive whereby a positive potential is applied to the line 150, so rendering audio amplifier 160 effective. This state persists after cessation of the positive voltage on line 108, due to capacitor 148 being charged, until the capacitor discharges. The positive potential applied to line 150 is also applied over circuit 155 to the D.C. amplifier transistor 131 whereby the preliminary stages 30 of the amplifier are also held conductive for an extended period. A manually operable switch 151 enables the user to retain the receiver in continuous operation when desired. Four tone calling arrangement.-A second arrangement is only rendered if the signal carrier is sequentially modulated with four different control tones, in the correct sequence. In the decoder, which receives demodulated signals on line 231, Fig. 6, the first tone is passed by a filter 241 to a rectifier 260: the complete modulation is passed to a rectifier 270 whereby rectifier 260 is so biased as to produce an output only when control tone is present. The output from rectifier 260 is applied to electronic switch 280 the output of which is applied to AND gate 290 which receives a seond input from inverter 420: if both inputs are present an output voltage is applied to timer 300. A D.C. voltage appears on conductor 303 for a duration dependent upon the setting of the timer 300, being applied to an electronic switch 310 which produces a D.C. voltage pulse on conductor 314 and switches filter 341 to pass the second control tone. This second control tone is rectified by rectifier 360 which is also biased from rectifier 270, the output from rectifier 360 operating switch 380: its output is applied to AND gate 390 which derives a second input from switch 310. The output from AND gate 390 operates a timer 400 so that a D.C. voltage appears on line 403 for a duration dependent upon the setting of the timer. This operates switch 410 the output from which is applied to reverse inverter 420 and also to the filter 241, which is thereby returned to pass the third tone. This third tone is rectified by rectifier 260 to operate electronic switch 280: AND gate 290 however is not thereby operated due to the absence of a record input from the now reversed inverter 420. The switch pulse passes through AND circuit 430 instead, thus now receiving a second input from switch 410. An output from AND circuit 430 is fed to electronic switch 410 so as to restore the inverter 400 and also via line 437 to timer 440. Timer 440 operates electronic switch 450 which applies a pulse to filter 341 which is thereby returned to pass the fourth control tone: this is rectified by rectifier 360 to operate electronic switch 380, but AND gate 390 is not thereby operated due to the absence of a second input from switch 314. The switch pulse passes, however through AND gate 460 instead, thus still receiving a second input from switch 450. The final output from AND gate 460 is applied to output line 465; an output is also applied via line 466 to reverse switch 450 whereby filter 341 is returned to the first control tone. A pulsed control circuit 470 is coupled to the outputs from switches 280, 380 and produces on line 473 a continuous output from the reception of the first control pulse until the cessation of the fourth. The specification also describes a transistor circuit for the decoder (Fig. 7, not shown). The pulse circuit 500, Fig. 9, is similar to that described with reference to item 120, Fig. 3, and this energizes the preliminary circuits of the receiver via line 516. A timer circuit 520 similar to that described with reference to item 140, Fig. 3 is also provided, operated by a control voltage on line 465. When timer 520 applies a bias to line 530 transistor 550 can be rendered conductive by pulses applied to its emitter from line 516, rendering similarly conductive transistor 551 and oscillator transistor 542 thereby producing a pulsed tone in loud-speaker 545. The control signal on line 465 is also applied to a bi-stable circuit 570 which biases line 581 whereby transistor 591 can be rendered conductive by pulses applied to its emitter from line 516, rendering transistors 592, 594 similarly conductive so as to pulse warning lamp 600. Circuit 570 also energizes line 582 to bias a transistor 611 conductive, thereby connecting a capacitor 613 in parallel with the capacitor 509 in pulser 500, so that the width of the pulses is increased. Bi-stable circuit 570 can only be reversed and the lamp 600 extinguished by opening of the manual switch 576a. The specification also describes an arrangement (Fig. 11, not shown) whereby the rate of pulsing of loud-speaker 545 and lamp 600 is dependent upon whether the fourth control tone is of less than, or persists beyond a predetermined duration, thereby permitting the transmission of two different signals.