Patent GB-660654-A (GB)
Title: Improvements relating to printing telegraph systems
IPC: H04L1/00
Filed: 1948-05-31
Abstract: 660,654. Multiplex type-printing telegraphy; electric synchronous movements. GRIFFITH, R. G. May 31, 1949 [May 31, 1948], No. 14699/48. Class 40 (iii). [Also in Group XL (c)] Each unit of a five-unit code is transmitted as a positive element followed by a negative element or vice versa. At the receiver, the first elements are used to produce normal units of corresponding sign and are also compared with the second elements and if these are not of opposite sign for any one unit due to mutilation during transmission, error conditions are set up and an error signal is printed. An allspacing or blank combination is used for this and in view of this the blank combination is not used for transmission and if encountered in the transmitting tape is automatically replaced by an all-marking shift signal. In one arrangement, each code combination is transmitted twice and an error signal is only printed if both transmissions are similarly mutilated or if both elements of one unit are inverted in one of the transmissions. The invention is applied to a four-channel multiplex system and at the receiver the reconstituted normal five-unit code may be converted into a start-stop code of the same total duration. Transmitting arrangements; tape transmitter, Fig. 2. Tape-controlled contact levers C1 ... C5 connect positive or negative battery to distributer contacts b ... f and b1 ... f1, the last three levers controlling storage relays D ... F so that the tape may be stepped on to set up a new combination as soon as the distributer brush B2 has left contact c or c1, contacts P1, P2 being opened at this time. The combination picked up by brush B2 is repeated by relay IRA to conductor 1. When an allspacing signal is set up on the tape, no positive potential is connected through diodes D1 ... D5 to the grid 23 of a gas-tube T1 so that tube T1 is extinguished and tube T2 is fired to operate relay A which causes an all-marking signal to be transmitted. The release magnet RM is energized to release the distributer for a half-revolution at the correct instant by a pulse over lead 10 from commutator RC, Fig. 3. Code-unit conversion; multiplex transmismission. Lines 28 ... 31, Fig. 4, represent on the same time-scale five-unit sequences recorded in four tape transmitters TTA ... TTD, Fig. 2, and commutator RC sends release pulses over leads 10 ... 13 at the instants corresponding to points 32 ... 35 respectively. Commutator SC transfers samples of the code units on leads 1 ... 4 from the four transmitters to the respective keyers AK ... DK, each sample being taken at the middle of a unit and the four messages being sampled in succession (at points 36 ... 39, Fig. 4). In each keyer the signal samples control a flip-flop valve V1 having its anodes 46, 45 connected respectively to pairs of anodes 47, 48 and 49, 50 in double-triode valves V2, V3. The voltages on the pairs of anodes for the code transmission 28 in the first channel are shown at 51, 52, Fig. 4. A light-chopper disc LC produces pulses at four-millisecond intervals in photo-electric cell PC1 and these pulses are distributed by commutator PD over eight brushes PD1 ... PD8, two pulses going to each keyer, the first to the left-hand grids of valves V2, V3 and the second to the right-hand grids. These pulses 53a, 53b, Fig. 4, bridge a four-millisecond interval in the middle of each code unit. If the code unit registered on valves V2, V3 is a positive one, valve V2 is rendered conductive over its left and right sections consecutively and correspondingly cathode potentials are fed over diodes D6, D7 to the grids of a flip-flop main transmitting relay V4 so that the 32-millisecond first (positive) unit of signal 28 is sent out as a four-millisecond positive element followed by a four-millisecond negative element, as shown at 68, Fig. 4. The first (negative) unit of the second channel is similarly sent as a negative element followed by a positive (69) and the resultant output signal is the combination of signals 68 ... 71 as shown at the top of Fig. 9. The Provisional Specification refers to an alternative conversion arrangement utilizing pairs of discharge lamps scanned by rotating mirrors and controlling pairs of photo-electric cells which produce the marking and spacing elements. Receiving arrangements; testing for mutilation. The incoming composite signal operates a flip-flop main receiving relay, Fig. 6 (not shown), which produces, for a positive signal, 75 volts negative potential on lead 86, Fig. 7, and 100 volts positive potential on lead 87, these potentials being reversed for a negative signal. Leads 86, 87 are connected to the anodes 98, 97 of triodes GS, GM. A photoelectric cell PC2 controlled by a light-chopper disc transmits impulses at 4-millisecond intervals to commutator DR which distributes the impulses in pairs to the four channels, the first of the pair for the A-channel going to the grids of triodes GS, GM. These pulses occur at the centres of the unit elements as shown at 1, 2, Fig. 9. With anode 97 at positive potential, triode GM conducts on the first pulse and the change of potential at its cathode causes flipflop valve R1 to be set in marking position and since the next pulse to triodes GM, GS (1a, Fig. 9) is 32 milliseconds later, a signal 108a corresponding to the original signal 28, Fig. 4, is set up on valve R1. The anodes of valve R1 are connected to the anodes of two triodes R2, R3, the grids of which are controlled by the second pulse from commutator DR. These valves are associated with a flip-flop valve R4 controlling the two windings of the output relay SR, the operation of which is thus delayed until the test for mutilation is made. The second pulse from commutator DR also passes to the grids of triodes HM, HS connected similarly to valves GM, GS. The cathodes of triodes HM, HS are connected respectively to the left and right anodes of two flip-flop valves R5, R6, the pairs of grids of which are oppositely connected to the anodes of valve R1. Thus, the left-hand grid of valve R5 and the right-hand grid of valve R6 are connected to anode 94. For a positive element followed by a negative element (or vice versa) the right (or left) section of valve R6 will have positive potential on both grid and anode and a positive potential from the cathode will be applied to grid 146 of flip-flop valve R7 to cause the operation of the upper windings of relays EA, EB to signify no mutilation. If both elements are of the same sign, relay R5 will operate to control valve R7 in the opposite direction to energize the lower windings of relays EA, EB to indicate a mutilation. The cathode outputs of the two halves of valve R5 are combined through diodes D8 for the control of valve R7 but are separately applied over leads 162, 163 to two pentodes, Fig. 8 (not shown), having glow-discharge lamps in their anode circuits to indicate whether mutilation has added a marking signal (due to noise) or a spacing signal (due to fading). The operations controlled by relays EA, EB are referred to in a later paragraph. Synchronizing, Figs. 10, 11. Potentials on leads 86, and/or 87 are connected through condensers 169 and/or 170 and a diode D9 to the left-hand grid of a gating valve GV, Fig. 10, producing pulses 173, 174, Fig. 11, at each change of sign. A further commutator SD on the main driving-shaft transmits gating pulses 176, one for each half-revolution, arranged, when synchronism is correct, to embrace the change of sign in the middle of a signal unit. These pulses are applied to anode 183 of valve GV and when a negative pulse 174 occurs during a gating pulse 176, the right-hand section of valve GV conducts and a synchronizing pulse 180 is produced at the cathode 182. A second light-chopper disc on the main shaft controls a photo-electric cell PC3 to produce a squarewave 179 which controls a flip-flop valve R8 placing positive battery alternately on advance and retard valves AV, RV. If pulse 180 is generated too early, advance valve AV operates to produce a short pulse which is applied from the cathode through a diode D10 to a valve CAV and stored on a condenser 191. When sufficient pulses have arrived to raise the charge on the condenser to a predetermined value, it fires a gas tube T3 operating relay SAR which energizes the armature of D.C. motor 77a to advance the stator of the synchronous motor driving the main shaft, Fig. 5 (not shown). A circuit over the right-hand section of diode D13 and resistance 190a prevents excessive charge on condenser 191 if, for example, advance pulses continue to arrive whilst phase-correction is in progress. When the phase has been advanced sufficiently, retard pulses operate valve RV to control tube T4 in a similar manner. The retard pulses also pass over lead 204 to the grid of an advance-reset valve ARV which operates at each pulse, and the consequent reduction of potential at point 209a extinguishes tube T3 and partially discharges condenser 191 over the right-hand section of diode D12 and resistance 209. By suitable choice of the value of resistance 209, the reduction of the potential on condenser 191 to a value insufficient to reoperate tube T3 can be made effective after more than one retard pulse so that a single retard pulse occurring, due to excessive distortion, during a succession of advance pulses will not interfere with the correction. Operation when error occurs; conversion to start-stop code. With the circuit arrangement shown in Fig. 13, the transmitter is modified to send each code combination twice and an error indication is only passed to the printer if the same unit is mutilated in both transmissions or is completely inverted in one transmission, e.g. from 68 to 69, Fig. 4. Three commutators C3 ... C5 are driven synchronously with the main shaft driving commutator DR, Fig. 7 &c. by an alternator geared to the shaft, Fig. 5 (not shown). Commutator C3 has two groups of five segments