GB1475339A - Radiotelephone station - Google Patents

Abstract

1475339 Automatic exchange systems THOMSON-CSF 5 Nov 1974 47882/74 Heading H4K A radio telephone station, including a telephone handset with a receiver and microphone has an additional audio monitoring device distinct from the handset receiver for producing a tone when a traffic channel is free. The radio system is of the type wherein a number of radio frequency channels are available for use by a number of mobile stations and a separate service channel is used for channel allocation from a central fixed station. The invention resides on the provision of a monitoring loud-speaker 14 which is only enabled when the handset 16 is on-hook and which, in addition to supplying ringing tone, is used to enable the mobile subscriber to initiate a call and monitor the progress of the call up to the point where the called station goes offhook, without his having to lift the handset 16. Indeed if the handset 16 is lifted before the called subscriber replies the call set up procedure is terminated. To initiate a call the mobile subscriber depresses a call button which operates contact A to set a bi-stable 34. A calling tone is then transmitted on the service channel by transceiver 40. The control station responds by sending a binary word indicative of a free channel or the service channel to cause the receiver 10 and transmitter 23 to automatically time to the allocated channel and to cause a transcoder 41 to supply the identity of the calling mobile to the transmitter 23 for transmission over the allocated channel. To guard against the possibility of two simultaneous requests for service. The control station transmits the identity back to the mobile or the allocated channel and if the received identity agrees with that of the mobile, a proceed to send tone is supplied to the loudspeaker 14. The mobile subscriber then signals the identity of the called subscriber using a keyboard 30 (Fig. 2, not shown) wherein each digit is represented by a single tone. The frequency generator comprises an audio frequency oscillator adapted to operate on eleven different frequencies, one of which corresponds to the calling tone. The central station calls the required station by transmitting on the service channel the station's identity followed by the identity of the frequency channel to be used. A ringing signal generator 32 is then enabled to supply a ringing tone to the loud-speaker 14 in the called station. A mobile subscriber can lock his unit against unauthorized use by use of a key which causes contact C to be opened.