GB625483A - Improvements in or relating to electrical signalling systems - Google Patents

Abstract

625,483. Radio signalling. GENERAL ELECTRIC CO., Ltd., and STENNING, L. C. April 23, 1947, No. 10866. [Class 40 (v)] Relates to a radio signalling system, in which communication between two of a given number of stations is established over a selected channel, the number of available channels being less than the number of stations. Means are provided at a first station, whereby on receipt of a signal from a second station, a channel identifying signal is transmitted which conditions the second station for communication over the selected frequency channel. The Figure shows six mobile stations, each comprising a transmitter and a receiver, and a static station having a transmitter and receiver associated with a guard channel, and with each of three communication channels. If say, mobile station 3 wishes to communicate with the static station, the receiver R3 monitors the guard channel on frequency f1, and if this is free, transmitter T3 transmits a tone modulated signal characteristic of mobile station 3 at frequency f2. On receipt of this signal, the static station transmitter Ta retransmits this tone modulation at frequency f1 to indicate to the mobile station that its first transmission was received, and this is used to condition the mobile station for the next signal from the static station, which indicates the channel to be used for communication. This channel identifying signal may consist of a number of impulses which automatically operate the tuning means of the mobile transmitter T3 and receiver R3' as described in Specification 572,918. Communication may then be established at frequency f3 between T3,R3 and Tc,Rc. If the various controlling signals are not correctly received, the mobile station apparatus recommences the sequence of operations. Means such as a uniselector device, may be used to indicate engaged channels at the static station. If the static station wishes to call say, mobile station 3, transmitter Ta first transmits a tone on frequency f1 which operates means at all the mobile stations to prevent them from initiating calls. This tone is then interrupted to form the impulse signal characteristic of mobile station 3, and means such as a. uniselector are provided so that the selected mobile station is conditioned to receive the next channel identifying signal while the remaining mobile stations revert to their normal stand-by condition. A calling device may be operated at the required mobile station.' The equipment at the static station may be extended to a telephone exchange, and the mobile stations may then be provided with dialling equipments for use after a channel has been allocated. The invention may be applied to the case of an aircraft wishing to communicate with a number of ground stations in different areas. The guard channel frequency is made common to all the ground stations, and the system is used to set the aircraft equipment to the particular frequency which the ground station is using at that time. More than one guard channel may be provided.