Patent GB-832632-A (GB)
Title: Improvements in or relating to time-division multiplex telegraph receivers
IPC: H04L5/24
Filed: 1956-05-24
Abstract: 832,632. Code telegraphy. SIEMENS & HALSKE A.G. May 24, 1956 [May 25, 1955], No. 16112/56. Class 40 (3). [Also in Group XL (c)] A time-division multiplex telegraph receiver responds to timing and intelligence elements transmitted as phase modulation of a carrier and distributes the elements that carry intelligence to their respective channels under the control of a counting chain which is stepped forward by a control pulse train synchronized by the timing circuits. The channel signal pulses which are sent as 180 degrees phase modulations of a carrier with a synchronizing or timing signal comprising a period of no phase modulation followed by a period of 90 degrees phase modulation are applied to a filter F1, Fig. 1, limiting amplifier BV to an amplifier EV and a demodulator EM providing negative and positive pulses corresponding to the zero and 180 degree phase modulations. Provision is made for ten channels, each cycle period of 20 milliseconds being divided into twelve equal intervals of 1.66 milliseconds. Ten intervals are allocated to the channels and two to the two parts of the synchronizing signal. The output of BV is also fed to a modulator circuit RM from which the output is fed via filter F2 and amplifier HV as an auxiliary frequency for demodulating the received signals in the circuit EM. A part of the output of the modulator EM is fed to the modulator RM so that for one polarity of the demodulated signal the phase of the signal output from RM is reversed so that the phase modulation is removed and an unmodulated auxiliary frequency is provided for demodulation. During the period when the 90 degrees modulation is received and the output of EM is zero an impulse is provided via the section Z1 of the distributer and a pulse generator IS to pass a pulse of predetermined polarity to the modulator RM so that the phase of the auxiliary carrier is determined for correct demodulation of the received signals during the ensuing cycle of the distributer Z1 ... Z12. The output pulses from the demodulator EM are passed to gates G1 ... G 10 corresponding to ten transmitter channels and opened in succession by the sections Z2 ... Z11 of the distributer so that the received impulses are passed to corresponding bi-stable circuits K1 ... K10 operating the contact members e1 ... e10 of relays E1 ... E10 to pass positive or negative pulses to the appropriate receiver channels. The relays E1 ... E10 remain in their operated positions for the cycle period of the distributer, which is arranged to be 20 ms., i.e. the time duration of a single element of the signals applied to the transmitter-channel. For the synchronization of the distributer Z1 ... Z12 with the incoming pulses, a part of the demodulated output at EM is fed via a rectifier circuit G1, filter TP and amplifier CV to a comparison circuit TS to which is also applied the output of a circuit RS producing rectangular pulses of a frequency corresponding to the period of the distributer cycle, i.e. 20 ms. The circuits G1, TP and CV are arranged to produce pulses at the periods during which the 90-degrees modulation of the carrier is detected, i.e. at the period when the section Z1 of the distributer is operative and producing a pulse. Owing to the delay imposed by the circuit G1, TP, CV, the circuit RS is arranged to be triggered by a pulse from the element Z2 of the distributer so that a comparison is made between the output of CV and a transition zone of the rectangular waveform from RS. Allowance is made for the difference between the delay caused by the circuit G1, TP, CV and the interval between the pulses produced by the elements Z1, Z2 and the arrangement is such that a deviation from exact synchronism results in the operation of the circuit TS to generate a positive or negative voltage which modifies the frequency of the pulse generator P controlling the operation of the distributer Z1 ... Z12. Detailed circuit arrangement, Fig. 3. The received signals after amplification in the valve VR1 are passed to a valve VR2 and also via a modulator M4 and filter F2 to a valve VR3, the outputs of the valves being applied through transformers MU1, MU2 to demodulating arrangements M1, M2, M3 allocated respectively to the message signals, the application of a voltage to the modulator M4 to derive the demodulating frequency and to the generation of the timing signal for control of the pulse generator comprising valves VR5, VR6, producing over conductor 1 a train of positive stepping pulses at a frequency of 600 p.p.s. A control voltage is applied to the modulator M4 via resistor W when the left-hand section of the double triode VR11 is conductive. The counting chain for distributing the received pulses to the channels N1 .... N10 comprises the valves V1 ... V12 of which the valves V2 ... V11 are allocated to the signal channels and the valves V12, V1 are utilized in connection with timing operations. Normally the valve VR7 is non-conductive, but the pulse produced during the period of the 90-degrees phase modulation makes the valve conducting. In the normal operation of the arrangement the contacts (a2)1 and (d2)1 are in the opposite positions from those indicated so that the distributer operates in the known manner. Also, in operation, the contact (d1)1 is closed so that the valve VR13 which is alternately conducting and non-conducting in response to the output of the valve VR6 and transformer NU applies a negative pulse to the anodes of the valves V1 ... V12 during one half of the channel period so that the sampling pulses for the information elements are limited to a portion of the channel period. The received code pulses which make conductor 4 positive in relation to conductor 5 or vice versa in association with a positive pulse from the cathode of the tube V2 ... V11 associated with the particular channel pass for channel 1, through a gate G1, G2 or G3, G4 to operate a trigger VR14 controlling a relay E1 having its contact member e1 connected to the channel N 1. The control of the distributer is effected by comparing the timing pulse produced by the' valve VR7 with the rectangular voltage produced by valve VR8 under control of pulses passed over conductors 6, 9 from the 2nd and 8th sections V2, V8 of the distributer. The valve. VR8 controls the generation of similar but delayed rectangular voltage waveforms from a double triode VR9, and the rectangular voltage waveform appearing at the left-hand anode is taken off through a relatively large capacitor C4. The delay is such that the waveform transitions coincide with the centres of timing pulses from VR7. A double triode VR10 having its two anode-cathode paths in parallel is biased by networks Gl2, Gl3 fed from transformer NU so that its two sections are normally non-conductive. The pulses from the valve VR7 makes both sections of the valve capable of conductivity and the positive and negative positions of the rectangular voltage waveform from VR9 charge the capacitor C2 in opposite senses. In the condition of synchronism the resultant charge on the capacitor C2 is zero or approximately so. The resultant voltage on the capacitor C2 is utilized to control the circuit of the oscillator comprising the valve VR5 to restore synchronism. The frequency is adjusted by means of a reactance valve VR4 connected in parallel with the frequency-controlling resonant circuit L1, C1 and having its grid connected to a centretapped secondary transformer SU to which is applied the voltage from the capacitor C2 in combination with a biasing voltage derived from a secondary winding of the transformer NU .and a bridge rectifier Gl1 and adjusted by the' potentiometer R2. Capacitor C2 is sufficiently small to permit rapid correction of synchronism, and is connected in shunt via a resistor with a capacitor C3 of large capacity which acquires the average voltage of capacitor C2 and serves to maintain a control voltage in the event of a temporary interruption of the timing pulses. The voltage across capacitor C3 is indicated by a centre-zero meter and permits potentiometer R2 to be adjusted to reduce the synchronizing control to a minimum. An arrangement involving relays A1, A2, B, D1 and D2 is provided to ensure that the counting chain V1-V12 is started at the correct phase when operations first commence. Contact (a2)1 and C2 break the counting chain between stages V1 and V2 and connects V2 to receive the timing pulses from VR7. The first timing pulse therefore triggers. the counting chain directly to start it at the correct phase and normal operation is introduced when relay B, which is a slow release relay, subsequently releases. Relay A which is operated by a trigger circuit VR12 triggered from stage V1 of. the counting chain also serves to operate an alarm if it is released due to an interruption of the counting operation due to a faulty stage. Fig. 4 (not shown), illustrates a modification in which the channel trigger circuits are replaced by pairs of thyratrons. The potentials from the cathodes of the counting chain serve to condition the thyratrons to conduct whilst actual conduction is effected by the stepping pulses from pulse generator VR5, VR6 over conductor 1, With this arrangement the signal pulses for the channels are effectively sampled only for a brief period at the centre of each, pulse.