Patent GB-600258-A (GB)
Title: Improvements in or relating to electric pulse communication systems
IPC: H04J3/00
Filed: 1945-01-05
Abstract: 600,258. Pulse multiplex signalling. STANDARD TELEPHONES & CABLES, Ltd. Jan. 5, 1945, No. 560. Convention date, Jan. 26, 1944. [Class 40 (v)] In a pulse communication system with a transmitting terminal, a receiving terminal and one or more branch terminals, which may be a multiplex system, means are provided at branch terminals for selecting demodulating and suppressing the pulses of a channel or channels and producing a further pulse train or trains in the transmission medium. The pulses in a typical multiplex system based on the invention are shown in Fig. 2 in which nine interlaced channels are taken as an example. From the west terminal eight channels are transmitted, channel 8 being omitted, curve a, and channel 1 being modulated with synchronizing signals. At a branch terminal A channels 1, 4, 9 are selected by increase of amplitude and clipping at level 90, curve b, and the remaining channels together with channel 1, further channels 4A, 9A inserted in the gaps left by suppression of channels 4, 9, curve c, and a further channel 8A, in the channel 8 gap, are passed on, curve d. At a branch terminal B channels 2, 5 are selected, curve e; and suppressed, curve f, new channels 2B, 5B being substituted therefor, curve g. At a third branch terminal C, channels 1, 3, 9A are selected, curve h, 3 and 9 are suppressed, curve i, and a new channel 9c re-inserted, curve j. Thus, the east terminal receives channels 1, 6, 7 from the west terminal, 4A, 8A from branch terminal A, 2B, 5B from branch terminal Band 9c from branch terminal C, intercommunication between branches A and C being provided by channel 9A. Similar transmission from the cast to the west terminal may also be provided. West terminal. At the west terminal the lines 101 ... 109, Fig. 3, from the signal sources are connected through hybrid coils 111 ... 119 to modulators 121...129 and through lines 110 to the demodulators associated with the incoming channels. A common base wave source 130 feeds all the modulators through individual phase-shifters 131 ... 139. The time modulated and interlaced pulses from the modulator outputs are passed to the communication medium 150 through switches 142 ... 149, no switch being provided in the synchronizing channel 1 which is always operative and switch 148 being open as channel 8 is not in use. A synchronizing signal source 151 of frequency f1 is connected to modulator 121. Two further synchronizing signal sources 152, 153, of frequencies f2, f3, are connected to switches 154, 155 through which they may be applied to modulators 122, 123, 125, 127 or 128. As shown, f2 is fed to channel 2 and f3 to channel 5. Branch terminals. At branch terminal A the synchronizing signal from channel 1 is used to synchronize a square wave pulse generator 231, Fig. 4, being selected from the incoming pulse train by deblocker selector 201, of the type 302, Fig. 10, described later, demodulator 211 and filter 221. The output of generator 231 is applied directly to selector 201 for channel 1 and through delay networks 204, 209 set to select channels 4, 9 in selectors 214, 219 fed with the incoming pulse train through switches 284, 289 and feeding demodulators 224, 229 and their associated signal reproducers. In order to suppress these channels in the transmitting medium 150, a channel suppressor 241 of the type shown in Fig. 9, described later, is provided. The control pulses for this circuit are derived from the outputs of delay networks 204, 209, which are reversed in phase in units 234, 239 and fed through mixer 240. To supply the three new channel pulse trains 4A, 8A, 9A to the transmission medium, a local base wave source 243 synchronized by the pulse generator 231 feeds modulators 254, 258, 259 through phase-shifters 244, 248, 249. The modulator outputs are applied to the transmission medium 150 through switches 274, 278, 279 and coupling circuits 264, 268, 269. Similar arrangements at branch terminals B and C are provided to select, suppress and produce desired channels, Fig. 5 (not shown). East terminal. At the east terminal, Fig. 6, the signals from 150 are applied to deblocking selectors 511 ... 519 through switches 501 ... , 509, of which 503 is open as no channel 3 signals are present. The deblocking oscillator 551 is synchronized by channel 1 signals from demodulator 521 and filter 541 and its output is fed to the selectors through delay networks 552 ... 559, and the subsequent demodulators 522 ... 529 feed the lines 572 ... 579 to the reproducers through hybrid coils 562 ... 569 to which are also connected the lines 580 leading from the channel modulators for outgoing signals from the terminal. Monitoring signals in channel 1 are separated by filter 531 and fed through hybrid coil 561 and line 571 to a receiver 581. Carrier signalling. When the signal pulses modulate a carrier, the west-east and east-west transmissions are on separate frequencies F1, F2. At a branch terminal, Fig. 11, F1, F2 are separated by filters 71, 81 detected at 72, 82 respectively and then applied to the deblocker demodulator circuits shown below the line A-A, Fig. 4. The suppression signals are applied to channel suppressors 73, 83 respectively in which an amplifier valve is biassed thereby. New channels are inserted by modulators 75, 85 which receive the carriers F1, F2 respectively from sources 74, 84 and feed their outputs to mixers 76, 86 connected to the transmission medium. Alternatively, the carrier frequencies may be radiated from aerials. . Pulse modulator. The production of a pulse train time modulated by a signal and a synchronizing source may be accomplished by the circuit of Fig. 8. The signal source 101 through filter 20, and the synchronizing source 151 are connected respectively to the grids of triodes 30, 31 whose parallel outputs are fed to the series-connected primaries of a mixing transformer 33. Energy from the base wave sinusoidal source 130 is applied to a further primary 36 and the secondary coils 37, 38 are connected to symmetrically biassed triode rectifiers 39, 40 with paralleled outputs connected to pulse shaper 41. The modulating currents upset the symmetry of the rectifier output 20A to produce output 20B of the same cadence frequency, but with displaced pulseproducing cusps. Deblocking selector and demodulator. The selector valve 61, Fig. 10, has the signal pulse train applied to one grid from line 60 and deblocking pulses from pulse generator 332 applied to another grid, connected to a diode D.C. restorer 62. When both grids are energized simultaneously, the signal pulse concerned appears in the output and is fed to one grid of a valve 63, another grid of which is connected to a circuit 64 tuned to a harmonic of the pulse cadence frequency. The resulting oscillatory pulses in the anode circuit have amplitudes depending on the spacing of the applied signal pulses and are passed through a low-pass filter 65 to give the demodulated signal output. If a synchronizing signal is present, it is selected by filter 322 and fed to the pulse generator 332. The remaining demodulated waves pass to the reproducing device through filter 382. Channel suppressor. Circuits suitable for the mixer 240 and channel suppressor 241, Fig. 4, are shown in Fig. 9. The mixer valve 240 receives, on its two input grids, suppressor pulses 51A, 52A derived as previously described. The combined output 53A is fed to triode 53, a suitable D.C. restorer 54, 55 being provided. The signal pulse train 50A is applied to a second triode 50 and the combined paralleled outputs 59A fed to a clipper valve 57 passing only those pulses which do not correspond to the suppressor pulses 51A, 52A. The invention is not confined to multiplex systems, but may be applied to select and suppress pulses in a line connecting several branches and to transmit remodulated pulses in place of those suppressed. Specification 600,252 is referred to.