Patent GB-706010-A (GB)
Title: Improvements in or relating to signalling arrangements for multi-channel telecommunication systems
Inventor: WRIGHT ESMOND PHILIP GOODWIN
IPC: H04J3/04
Filed: 1950-02-28
Abstract: 706,010. Voice-frequency signalling; multiplex systems. STANDARD TELEPHONES & CABLES, Ltd. Feb. 23, 1951 [Feb. 28, 1950], No. 5074/50. Class 40 (4) [Also in Group XL (b)] In a multi-channel carrier current communication system, two-way supervisory signals for all the channels are transmitted over a narrow band telegraph channel in one of the communication channels by time-division multiplex. The 12-channel system shown employs an electronic distributer, comprising multi-gap cold cathode gas , discharge tubes of the type described in Specifications 639,827, [Group XL (b)], and 692,415, [Group XL (a)], which is stepped at 50 steps per second by pulses derived from a basic 4 Kc. frequency in the carrier system. The distributers are pulsed from separate sources and have 28 outlets which are allocated two per channel for the transmission of a two-unit code and the remainder for synchronizing. The distributer, Fig. 4, comprising the tubes MCC, MCD, MCE and CF, is stepped by positive pulses on rectifiers MR 4-10 which are derived from the cathode of tube SD, Fig. 3, at each 80th pulse of the 4 Kc supply connected to the gate TGA of the tube MCA. The asterisks in the tubes denote the rest position which can be established by a -ve pulse on the restore lead R; such a negative pulse is applied by the start switch KR and by the stop tube SZ. The controlled station, Figs. 5 and 6, is supplied with pulses from two sources # 1  and # 2  which are 180 degrees out of phase and minor corrections of asynchronism are made by inserting an additional pulse from # 2  between the normal stepping pulses from # 1  when the distributer is slow and by suppressing one of the pulses from # 1  when the distributer is fast. This is achieved by comparing the distributer stepping with the reversals in the incoming signals. A synchronism control tube SB is fired on step MCA K10 and MCB K4 of the divide-by-80 arrangement, and on each succeeding step until at step MCA K9 and MCB K8 a tube CB fires and extinguishes SB. From MCA K10 and MCB K8 a tube FB is fired, extinguishing CB and remains fired until SB refires on the next cycle. The cathode potentials from these three tubes are applied to tubes C, S and F together with a positive pulse derived from a pulse change in the incoming signal which is detected by tubes RM, RS and applied over a transformer PTI. Correction is effected according to which of the tubes CB, SB, FB is firing at the time of the pulse change. To guard against the distributers getting out of step a " phasing " signal is transmitted which comprises a "mark" on the final step of the distributer followed by a " space " on the first three steps of the next cycle, and when examination reveals a '' mark " whilst the controlled distributer is on any of the first three steps, tube SDA strikes and ' fires a stop tube SZ which trips a start tube ST and sends a negative pulse over the R lead. The following reversal causes the start tube to restrike and the " out of phase " detector checks again for the three spacing elements and so on until the spacing elements appear in their correct position. A tube OSO is struck at the end of each distributer cycle but with SDA fired due to an out of phase condition, OSA fires and quenches OSO. The +ve bias on a rectifier MR 64, connected to the trigger of a tube BA rises slowly due to a resistance R1 and condenser C1 in the cathode circuit of OSA and if OSA does not restrike after a predetermined interval tube BA strikes to release a relay AL which removes the anode supply from the synchronizing and phasing alarms operates the appropriate alarms and restores the distributer to its idle condition. Further reversals cannot then restart the distributer. Distributer stop alarm arrangements also trigger the tube BA and if necessary an alarm can be sent over the phasing positions to the controlling station. The switchboard, Fig. 1, is connected to an outgoing relay set which sends and acknowledges inter-exchange supervisory signals and keys VF dialling pulses over the carrier channel. The two-element supervisory signals key an oscillator-modulator OM through a sender in the periods allotted by the distributer, and the oscillations pass to line through a band pass filter BP to a telegraph receiver, Fig. 2, at the distant end. Here the distributer allots the incoming signals to their corresponding relay set which connects a voice-frequency receiver VR to the appropriate carrier channel and the received digits step the automatic switches. Supervisory signals are returned from the incoming relay set. The insertion of the operator's plug, Figs. 9 and 10, operates a relay M which prepares a holding circuit and energizes a rejay MM to remove a " wetting " potential from the line, start a flicker earth, operate a relay MX and send a seize signal " mark-mark " by earthing a line AS to the sender. The two signal elements of the channel described are sent on points 4 and 5 of the distributer and the oscillator is controlled by the potential on lines AS and BS at the time that the rectifiers MR75 and MR76, Fig. 7, are biased +ve by the firing of MCC K4 and K5 respectively. A proceed-to-dial signal " mark-mark " is sent back over distributer points MCD K9 and MCE K1 and, to avoid distortion, the incoming signals are sampled only when a +ve potential is developed on MCA K1 MCB K5 and on the appropriate distributer point, i.e. a central portion of the signal. Relays ARA and BRA in the detector, Fig. 7, respond to a " mark " on the first element and a "space" on the second element respectively to operate relays MA and SB in the relay set. The returned proceed-to-dial signal operates relay MA to lock MS, which had previously marked the line busy, and replaces the full earth on the high resistance winding of relay M by the flicker earth to flicker the operator's supervisory lamp. The operator then throws a dial key to energize relay AM, which in turn energizes a relay DT to prepare the dialling out circuit, prepares relay LR and fully lights the supervisory lamp. VF impulses are keyed to the line by relay AM in response to the dialled digits. Relay LR, when operated by the restoration of the dial key, prevents false line signals by holding the relay AM and releases relay DT which operates a relay LRR to complete the speech circuit and maintain the supervisory lamp. LRR sends " mark-space " an end-of-dialling signal which releases the distant VF receiver and relay AM releases. When the called party answers, both relays MA and SB are operated and the supervisory lamp is dimmed. Relay SB restores and the supervisory lamp is again fully lighted when a called party clear " mark-mark " signal is received and the operator in clearing releases M, MM, LR and LRR to send a releasing " space-mark " signal to release the distant automatic equipment. On release a "space-mark " fully-clear. signal is returned and relays MA and MS are released.  The seize signal operates relay MA in the I/C relay set, Fig. 11 and 12, to start the VF connector, Fig. 13, hunting for the calling circuit and operates a relay MAA to complete a test and switching circuit. Relay ST in the VF connector is operated by the earth applied to the start line by relay MA. It connects a test relay TR to arc H and completes the stepping circuit to a uniselector LF. When the wiper of H finds battery, relay TR operates to cut the drive and operate a relay K, which locks up, connects the incoming dialling pulses to the VF receiver and operates a relay KR to maintain a supervisory lamp LS and release the start relay ST. The relay TR also extends a low resistance earth to the contact on arc H for guard purposes. Relay AR is energized over the A line by a contact of relay KR and it completes a line loop to pick up a group selector. Earth on the P wire operates relay RG which sends the proceed-to-dial signal by earthing line AS. The incoming dialling pulses are repeated by the VF receiver as D.C. impulses to relay AR which sets the switches accordingly..The end-of-dialling signal operates relay SB as well as MA and relay SB in operating a relay SBA releases relays MA and MAA, the latter releasing slowly. Should delay occur before dialling is commenced an S pulse on lead PS operates a relay SP which locks up and prepares a relay CL for operation by a Z pulse on lead PZ. Should CL be operated, relay MAA releases, releasing in turn relays AR, B and RG, which sends back a line-free signal and restores MAA at the calling end. Although dialling over the telegraph channel is not possible, key pulsing or register-to-register selection may be sent over an additional telegraph channel. Termination arrangements for connecting a transmission terminal incorporating a signalling terminal to an exchange are described with reference to Fig. 14 (not shown). The signals between the exchange and the signalling terminal are conveyed over a " half duplex " earth return telegraph channel in each leg of the speech conductor. In a modification, Fig. 15, (not shown), one of the speech lines is used for signalling in each direction and the signals are effected by three current conditions, i.e., no current, low current and heavy current. The output of an oscillator of the oscillator modulator, Fig. 14 (Prov.) (not shown) is fed to line via transformers and rectifier networks. The latter is controlled by a flip-flop arrangement which responds to the multiplex sender. Conventional VF receivers are described with reference to Figs. 15, 16 and 22 (Prov.) (not shown).