Patent GB-741541-A (GB)
Title: A simplex radio-telephone system comprising a fixed station and a plurality of mobile stations
Inventor: LUTZ ANTONIUS JOHANNES
IPC: H04W88/02
Filed: 1951-01-11
Abstract: 741,541. Exchange systems. STAATSBEDRIJF DER POSTERIJEN, TELEGRAPHIE EN TELEFONIE. Jan. 11, 1951 [Jan. 14, 1950], No. 857/51. Class 40 (4). [Also in Group XL (c)] Mobile stations have access over radio links to a switchboard at a fixed station. When a mobile station calls the fixed station on a carrier YY common to all mobile stations, the fixed station returns a carrier XX which disables both the speech and calling signal receivers at all other mobile stations. The fixed station carrier XX is transmitted continuously for the duration of the call. Telephone receivers in the mobile stations are cut off during transmission of YY and YY is cut off during reception. The fixed station calls a mobile station by transmitting dialled impulses as interruptions in a modulation on the carrier XX. A selector is driven by the impulses at each mobile station but the called number is recognised only at the called station which transmits the carrier YY when the call is answered. Fixed station switchboard, Fig. 1. An incoming carrier YY from a calling station operates relays AD, CD and BD follows after a delay. A calling signal is given by lamp OL, relay ED pulls up and relays PH, DD, P follow with transmitting lamp ZL. Relay P starts the transmitter (not shown) for carrier XX. Incoming speech is transmitted to the operator at switchboard BP over contacts cd1, cd2 and line aa, bb. When the incoming speech ceases, the carrier YY is cut off at the calling station, CD falls back and outgoing speech is transmitted over transformer Tr to the transmitter. The operator answers a call by pressing key S2. Relay Z pulls up and relays PH, DD, P are held independently of relay ED and the incoming carrier YY. To call a mobile station, the operator presses key S2 and dials the number to generate pulses at i. Relay Z pulls up over off-normal dial contacts ac. The transmitter is started as before but relay DD does not operate and allows relays A, X to pull up and start a modulation generator KG which is connected to the transformer Tr over contacts x1, x2. The modulations are interrupted by an impulsing relay contact a2. A call can be ended by throwing switch S2. Mobile station, Fig. 2. Switch S1 is closed when the station is in service. To make a call, a microphone key Mt is operated and relays B, P pull up. Relay B locks and P starts the transmitter which stops whenever Mt is released. The microphone M is linked to the transmitter by means of transformer Tr2. When the fixed station carrier XX is received, relay FD pulls up after a delay. A telephone receiver T and a loudspeaker L are linked to the output valve VB by a transformer which is short-circuited by relay P during transmission of XX. If the fixed station calls, the modulation frequency is detected by valve VB and relays S, V pull up before FD. Impulses operate the driving magnet Dr of the switch SK and at the end of the digit, dialling relay V falls back, VS pulls up and the detector valve VB is cut off. If the number transmitted is the number of the station (5), relay B pulls up over contact 5 of the first bank of SK. At the end of a call, the carrier XX is cut off at the fixed station, FD falls back and condenser Co discharges through B to release it. Specification 677,836 is referred to.