Patent GB-703322-A (GB)
Title: Time division multiplex system
IPC: H04J3/08
Filed: 1949-02-23
Abstract: 703,322. Telephone exchange systems. HOMRIGHOUS, J. H. Feb. 23, 1949 [March 5, 1948], No. 4985/49. Class 40 (4) [Also in Groups XL (a) and XL (c)] In a pulse multiplex radio-telephone system having a master station and a number of substations the transmission and receiving times at the substations are determined by control pulses, characteristic of the substation, which are transmitted by the master station. Each channel is allocated three consecutive time positions in a distributer cycle, the first position being taken up by the transmission of control pulses characteristic of the outstation it is intended to control. In a system in which dialling is not contemplated, the same radiofrequency is used in both directions, the second and third time positions being used respectively for outward and inward transmission. In systems in which dialling is contemplated different radio-frequencies are used for outward and inward transmission, the second time position being used for speech or like transmission and the third time position for the transmission of signals controlling the setting up and maintenance of automatic connections. The circuit of Figs. 4 and 5 is a composite one which includes all possible embodiments of both the master station and the substations. In practice much will be omitted. Thus for a substation the pulse generating equipment of Fig. 4 is eliminated. For a master station the. timing equipment incorporating valves 189, 171<SP>1</SP>, 172<SP>1</SP>, 181<SP>1</SP>, 171, 172 and 181 is eliminated. If non-automatic working is used the right-hand halves of valves 166, 206, 210 are not present. A choice of methods of signalling is presented over switch 197 which also determines whether the incoming speech currents are fed to an automatic or manual exchange or merely to a local telephone. Generation of control pulses at master station, Fig. 4.-Saw-tooth potentials developed by the charging of condenser 65 are applied to valve 68 which provides deflecting potentials for the cathode ray tube 74 whose beam is caused to sweep successively the electrodes 79 . . . 90. Negative pulses derived from electrodes 79, 82, 85, 88 are applied respectively to the left- and right-hand halves of valve 99 and the left-hand halves of valves 100, 101 thereby producing successively low positive, high positive, low negative and high negative control pulses on lead 103 the right-hand halves of valves 100, 101 acting as phase inverters. The pulses from electrodes 79, 82, 85, 88 are also applied to valve 107 to produce a succession of equal amplitude pulses on lead 110 for gating the station control pulses through a, pre-amplifier 227, Fig. 5. Pulses derived from electrodes 80, 83, 86, 89 are amplified in valves 120, 121 to produce pulses over leads 126 ... 129 for modulation by signals outgoing to the respective substations in pre-amplifiers 206, 224 . . . 226. These pulses are also combined with those from electrodes 79, 82, 85, 88 (after the latter have passed through valves 107, 108) and fed to valve 130 whose output over lead 133 enables the transmitter at the first and second time positions of all the outstations. Pulses derived from electrodes 81, 84, 87, 90 are amplified in valves 142, 143 and fed over leads 148 . . . 151 for enabling the receive power amplifiers 166, 234 ... 236 corresponding to the four outstations at their respective. third time positions. The pulse from electrode 90 also causes 67 to discharge the condenser 65 to cause the beam to fly back during which period valve 153 cuts off the cathode ray. Operation of master station, non-automatic.- Switch 158 is put in position 1 and switch 233 thrown to connect up the receive amplifiers 234 ... 236. Switch 203 is in its third position in which the transmit and receive amplifiers 206, 224 . . . 226, and 166, 234 ... 236 of all channels are connected to appropriate exchange equipments 237 ... 240 to be described later. Calling signals may be sent by applying tone from source 201 to valve 206 to valve 206 by key 204. The frequency used may be different for each outstation so that selective calling may be obtained, if one time position is shared by more than one outstation. Alternatively vocal paging may be used. Operation of outstations, non-automatic.- According as the selecting switch 158 is in its second ... fifth position the outstation responds to low positive, high positive, low negative, or high negative control pulses. With the switch in the second position incoming control pulses are passed to valves 171, 172. Valve 172 responds only to low amplitude positive pulses since high amplitude positive pulses cause 171 to conduct also thereby cutting off 172 on its second grid. With the switch 158 in its third position valve 172 is biased so as only to respond to high amplitude pulses and valve 171 is disabled. Anode current in 172 causes its fluorescent anode to glow causing the photo-cell 176'to produce a slightly delayed pulse which enables the receive power amplifier 166 over its left-hand half during the second time position to pass the received signals to the loudspeaker 196. The pulse from valve 172 is passed to a similar valve 181 to produce a further delayed pulse in the third time position  which enables the pre-amplifier 206 and the transmitter amplifier 210 over their left-hand halves whereby speech from the microphone 202 is transmitted. Valves 1711, 172<SP>1</SP> and 181<SP>1</SP> operate in a similar manner to 171, 172, 181 when 158 is in its fourth and fifth positions to respond to the low and high amplitude negative pulses which are fed to them via a phase inverter 189. Signalling is effected by applying calling frequency from the source 201 to the left-hand side of valve 206 by means of key 204. To call another outstation of the same group switch 158 is set to the position corresponding to that outstation and key 214 operated to interchange the transmitting and receiving time positions of the calling outstation. Operation of master station, automatic working.-At the master station switch 232 is thrown so that third time position pulses from leads 148 . . . 151 may enable the righthand halves of valves 206, 210 for transmission of tone from source 201 which may be interrupted by the dial 215. Alternatively a 2-tone code may be used, introduced by cam contacts operated by a dial member 305. Incoming dial-interrupted tone is taken via the righthand half of valve 166, which is also enabled during the third time position, to the exchange equipment 237<SP>1</SP>. The left-hand halves of valves 166, 206 and 210 are energized for transmission and reception of speech in the second time position. Operation of outstation, automatic working.- Switches 310, 311 are thrown to their alternative positions. In these positions the lefthand sides of valves 166,206, 210 are energized in the second time positions for transmission of speech and the right-hand side for transmission of dialling signals and the reception of 2-tone ringing code if such is used. Operator's equipment at master station, Fig. 6.-To call an outstation, the operator throws key 204 to connect ringing tone to the grid 205 of valve 206. Tones of different frequencies may be used for each subscriber. Or the operator may connect dial interrupted tone to the grid 217 of valve 206 thereby signalling the called substation by an audible code or by means of a code ringing selector thereat. Incoming ringing tone from valve 166 is amplified by the right-hand half of valve 261 and applied to the grid of valve 262. During the positive half-cycles the fluorescent anode is activated to maintain the photo-cell 264 energized through the whole of the ringing period to cause the right-hand of valve 261 to conduct and bring up relay 267 which lights a calling lamp. The speaking circuit over transformers 250, 251 may be connected to outgoing lines by the operator in the usual way. Automatic equipment at master station Fig. 7.-Incoming tone is applied via valves 283, 287 to operate relay 288 which then repeats the dial impulses to the exchange line which is closed by the slow-to-release relay 289, 294 operating during the dial train to provide a clean impulsing loop. Outgoing calls are completed via an operator.