Patent GB-694951-A (GB)
Title: Electric multichannel impulse communication system with inconstant impulse repetition frequency
IPC: H04J3/16
Filed: 1950-01-12
Abstract: 694,951. Multiplex pulse signalling. COMPANHIA PORTUGUESA RADIO MARCONI. Jan. 12, 1950 [Jan. 12, 1949], No. 860/50. Class 40 (v). In a multichannel pulse communication system, the modulated pulses or code groups of the individual channels are interlaced with those of the other channels, but the number of pulses or code groups transmitted for an individual channel, in any given interval, depends upon the channel signal complexity, measured for example by the rate of change of signal amplitude relative to those of the other channels, each channel pulse or code group being preceded by a channel-identifying signal. Transmitter.-Each channel circuit at the transmitter has a circuit B, Fig. 2, fed by the input signal, which generates a voltage dependent upon the complexity of the signal and which may, for example, be a differentiating or quantizing circuit. The output from circuit B feeds a storage circuit C connected to one of the fixed channel contacts of a rotary selector switch F. In practice selector F is an electronic switch described below in connection with Fig. 2 (b). For each cycle of operation, the switch starts rotating from position O, the selector driver G receiving a starting pulse from the synchronizing circuit H. When the selector F reaches, for example, the channel 1 contact 28 and the voltage stored in circuit C and thereby applied to limiter I, is sufficiently great to produce an output from the latter, this output is fed over lead 4 to stop the driver G. The switch therefore rests at the channel 1 contacts, two of which are short-circuited to prepare a switch E which places the channel-identifying signal generator D in operative condition. A pulse from circuit H over lead 2 then operates the generator D which delivers the identifying code signal over lead 2a to the output amplifier L and lead 23. Thereafter the switch E closes a switch A to connect the channel signal to the sampler and coder K which generates a pulse code group which is fed over lead 3a to the output circuit. The coder is controlled by a pulse from circuit H over lead 3. The storage circuit C is discharged by a pulse, over lead 5, generated by switch E when switch A is closed. A further pulse from circuit H now restarts the movement of selector F which moves until it reaches the contacts of another channel capable of producing a stopping pulse at the output of limiter I, whereupon the next identifying code signal and channel pulse code group are generated in succession as before. To act as a synchronizing signal, the identifying signal for channel 1 is transmitted when switch F passes position O. An automatic sensitivity control A.S.C. connected to all the storage circuits C adjusts the limit of circuit I according to the number of channels exhibiting high complexity. Alternatively, resistances in parallel with tne storage circuits may be automatically regulated. Receiver.-At the receiver, a synchronizer E, Fig. 10, fed from the filter F, supplied with the incoming signals from amplifier D, operates a switch C. By this means the channel-identifying signals are fed to the driver G which positions the selector switch A to connect to the appropriate channel and the channel signal is then switched to the decoder B, the output of which feeds the selected channel circuit. Tne reconstituted signal sample is stored in circuit H wnich is discharged at an appropriate time determined by a timer I. The identifying signals may comprise a binary, ternary, &c. code group and the channel signals may consist of amplitude modulated pulses and the two signals may be A.C. impulses of different frequencies transmitted simultaneously. The circuit B, Fig. 2, may consist of a transformer or resistance-capacitance differentiating circuit. Alternatively, a quantizing circuit fed by the signal may deliver pulses to the storage circuit when the amplitude changes by one or two quanta and these pulses may be of different polarity according to the sign of the amplitude change. In another arrangement, the circuit B comprises a number of parallel-connected band-pass filters of different pass bands, but between them covering the signal band and conneted to the storage circuit through attenuators the factor of which depends upon the pass gand, Fig. 3 (not shown). An electronic selector switch which performs the functions of the switch F, Fig. 2, is described, Fig. 2 (b). This is a n-channel arrangement in which three of the channel circuits are shown, each of which comprises four valves, e.g. 143 ... 146 for channel 1. The complexity-dependent voltages are supplied from terminals 28 over phase inverters 147 to the second control grids of the first valves 143, 152, 156, which are biased beyond cut-off. Assuming all these valves are cut off to start operation, closure of switch 160 charges condenser 161, the charging current producing a pulse in transformer 163. A scanning pulse, delayed in circuit 165, is thus fed to transformer 166 and is applied to the normally cut-off first control grid of valve 152. The ensuing screen-grid pulse in this valve is fed to the first control grid of valve 156 through transformers 168, 170 and delay circuit 169. This scanning process continues through the channel circuits, channel 1 being operated by the channel n valve 156 through transformers 171, 151 and delay circuit 172. When a channel is producing a high enough complexitydependent voltage to overcome the bias on the second control grid of its first valve, say valve 152, channel 2, a negative pulse at the anode thereof triggers the multivibrator 153, 154 which has one stable position. From the anode of valve 153 a positive pulse is fed to terminal 29 to initiate signal sampling and discharge of the storage device. At a predetermined time thereafter, a pulse from the anode of valve 154 is fed through valve 155 to transformer 170 to recommence the scanning cycle. The scanning is stopped as soon as any channel triggers its multivibrator due to the high positive voltage produced in the cathode resistor 195 which is common to all the first valves 143, 152, 156 and the multivibrator valves 145, 154, 158.