GB1294956A - - Google Patents

Abstract

1294956 Radio signalling ROBERT BOSCH ELEKTRONIK GmbH 20 Feb 1970 [22 Feb 1969] 8312/70 Heading H4L In a calling arrangement for radio telephony, in which a calling signal consists of a sequence of audio-frequencies, a plurality of resonant circuits tuned to the audio-frequencies forming the calling signals are switched into circuit under the control of a counter, a single counter being used both for transmission and reception of the calling signals. Reception of calling signal.-As shown in Fig. 1, the subscriber's station normally is prepared to receive a calling signal with the counter 22 at its start position supplying an output 24 and bi-stable 35 supplying an output 49 so that transistors 18 and 21 are conductive to tune the circuit 7, 8 to the first audio-frequency of the sequence. The calling sequence, demodulated at 45 is fed via a limiter 9 and coupling coil 10 to the tuned circuit 7, 8. If the first audiofrequency is correct the output of the tuned circuit is rectified at 30 and supplied via normally closed switch 32, delay 31 and OR gate 33 to step the counter 22 to its second position, and to set a monostable 34. This opens transistor switch 18 and closes switch 19 so that the circuit 7, 8 is tuned to the second audio-frequency of the sequence, which if it is correct, causes the circuit 7, 8 to be tuned to the third and last audio-frequency. If the third audio-frequency is correct, the counter is stepped to position 4 and the resulting output via delay 36 returns the counter to its initial position and via a lead 59 triggers a bi-stable 38 to switch on a warning lamp 42 and connect the loud-speaker 47 via switch 46. When the conversation is terminated, a switch 41 is manually operated to reset the bi-stable 38 and mute the receiver. If an incomplete calling signal is received the monostable 34 is reset to its stable state and returns, the counter to its initial position. Transmission of calling signal.-To initiate a call the call button 37 is depressed momentarily to set a bi-stable 48, thereby to change over bi-stable 35 to open switch 21 and close switch 17. The output of bi-stable 48 also opens switch 32, opens switch 5 to disconnect microphone 6, closes switch 29 to switch on an audio-frequency oscillator 12 whose output frequency is determined by the circuit 7, 8 and starts a multivibrator 40. Initially, the counter 22 is at position 1 so that transistor switch 14 is conductive, the resulting audio-frequency modulating the transmitter via input 70. The counter 22 is stepped up at each period of the multivibrator 40 whereby the transmitter is modulated by a predetermined sequence of audio-frequencies forming the calling signal. When the counter reaches position 4, the counter is reset to its start position via delay 36 and bi-stables 35, 38, 48 are also triggered to their other stable state. This reconnects the microphone, disconnects the oscillator 12, closes switch 32, connects the loudspeaker and switches on the lamp 42. When the conversation terminates the switch 41 is operated to return the circuit to its normal state prepared to receive a call.