GB829910A - Improvements in or relating to time-division multiplex telegraph transmitters - Google Patents

Abstract

829,910. Multiplex code telegraphy. SIEMENS & HALSKE A.G. May 11, 1956 [May 12, 1955], No. 14750/56. Class 40 (3). In a time-division multiplex telegraph transmitter in which each telegraph channel is explored in succession for a period approximately equal to the period of a channel pulse divided by the number of channels, the exploration is controlled by a single counting chain stepped forward by a timing pulse train consisting of two component pulse trains which control alternate stages in the counting chain and operate to step the counting chain through all its stages during the period of a channel pulse. Diagrammatic arrangement, Fig. 1.-Output at 300 c.p.s. from an oscillator S1 is squared, differentiated and rectified at DG to produce pulses at a frequency of 600 per second, which are applied to alternate stages of the counter Z ... Z12 of which the stages Z2 ... Z 11 are employed for channels A1 ... A10, and the stages Z1, Z12 for the provision of a synchronizing pulse. The pulses from S1 are also passed through a phase-shifter Ph and a dividing and shaping circuit H to produce pulses at a frequency of 50 per second corresponding to the time duration of a channel code element; e.g. 20 msecs. The stage Z1 can be triggered solely by the coincidence of pulses from DG and H so that the counter cycle is completed in 20 msecs. and channel pulses are applied to the individual gates N1 ... N10 for a period corresponding to 1¢ msecs. The corresponding code elements from the channels A1 ... A10 are also applied to the gates so that positive pulses pass to the amplifier P and a modulator M2. The pulses from H also pass to a sawtooth generator J and over the connection 5, 6 to a modulator M1 associated with a generator S2 of an audio frequency carrier. The signals may be utilized for amplitude or frequency modulation of the carrier, but in the arrangement described the positive pulses applied to the modulator M2 produce in the carrier a phase shift of 180 degrees. The pulses fed over the connection 5, 6 are utilized to effect in the modulator M1 and circuit arrangement T2, a phase-shift of 90 degrees in the carrier. Detailed circuit arrangement, Fig. 3. The 300 c.p.s. oscillations from the valve V1 and tuned circuit K1, L1 are applied by winding I of transformer T1 the circuit E and a transformer D having the mid-point of its secondary winding connected to rectifiers G19, G20 so that pulses at a frequency of 300 pass to the separate conductors 2a, 2b which are connected to the firing electrodes of cold-cathode discharge tubes Xl, X3 ... X11 and X2, X4 ... X12. Pulses from the winding II of the transformer T are also applied to the grid of a valve V2 having its anode circuit tuned by K2, L2 to a frequency of 50 c.p.s. Pulses at this frequency are applied from cathode resistor W3 to the firing electrode of the tube X1 which is then fired by a simultaneous pulse over conductor 2a and primes the tube X2 for exploring the pulse to be transmitted from channel A1. When the tube X2 is fired by the. pulse over conductor 2b a positive pulse is applied to rectifier G2 and if a positive pulse is present on channel A1 with which is associated rectifier G1, a positive pulse passes over conductor 3 to the grid of the valve V5 which is effective in the modulator M2 to change the phase of the carrier by 180 degrees. The carrier frequency produced by the valve V4 and its tuned circuit is applied by a transformer L3 to a modulator M1 to which is also applied the sawtooth voltage generated at a frequency of 50 c.p.s. by the valve V3 controlled from the screen grid of the valve V2. The fly-back period of the sawtooth voltage is equal to the length of the pulse applied over the line 1 to the tube X1 and during this period the phase of the carrier is changed by 90 degrees and the positive pulses applied over line 3 to the modulator M2 change the phase by 180 degrees. At the beginning of the next cycle of the counting ring the phase of the carrier is shifted through 90 degrees and the positive signals effect a relative phase shift of 180 degrees. At the beginning of each cycle of the counting or distributer cycle the phase of the carrier is shifted through 90 degrees-i.e. from 0 to 90, 90 to 180, 180 to 270 and 270 to 360 relative to its originalp hase and during the various cycles the positive signals produce a 180 degree phase-shift in the phasemodified carrier. In a modified arrangement, Figs. 2, 5 (not shown), the counting arrangement operates as a ring with the final or 12th cold cathode tube, when conducting, providing a priming potential for the first tube of the ring which is fired by a pulse on the conductor 2a. A pulse provided by the firing of the first tube controls a resistance capacitor circuit and a valve to generate the sawtooth waves having a period equal to that of the scanning cycle and utilized to produce the synchronizing pulses. A relay connected in the anode circuits of the tubes of the counting ring is normally energized when the counting ring is in operation but released when the power supply is cut off and the ring is inoperative. At its released contact it applies a priming potential to the first tube when the power supply is connected so that a pulse over the line 2a brings the ring into operation. The relay may be released and actuate an alarm if the distributer fails to cycle and one of its valves remains continuously conducting.