Patent GB-275538-A (GB)
Title: Telegraph system
IPC: H03M5/00
Filed: 1926-09-23
Abstract: 275,538. Western Union Telegraph Co., (Assignees of Nelson, C. F.). Aug. 6, 1926, [Convention date]. Systems using code elements and spaces distinguished by duration and polarity of current; perforated strip transmitters; repeating systems using contact-making relays; synchronous movements. - Comprises. means for enabling doublecurrent relays to be used for three-element-code telegraphy. Thus, signals comprising plus, minus, and zero elements are translated at the transmitting station into signals comprising plus and minus elements only, and these are retranslated at the receiving station into signals in the original code. Synchronisation is affected by the signals, and synchronising impulses are automatically transmitted when the type has run out. Code. A tape, Fig. 1<a>, may be perforated with holes such as 4a on one side to represent dots and holes such as 4b on the other side to represent dashes, while a space, 4<c>, is represented by the absence of a hole. Such a tape when used in the usual way gives line signals as shown in Fig. 2a, where c1 represents a dot, c2 a dash, c3 a space, but when used in the apparatus at the transmitting station A, Fig. 1, it yields line signals, as shown in Fig. 2<b>, where a dot d1 is represented by + -, a dash d2 by ++, and a space d<3> by - -. Similarly, signals of the kind shown in Fig. 2<a> when received over a cable are translated by the retransmitting system shown in Fig. 2, where the message is received on the cable relays CDR1, CDR2, and retransmitted over the line L2. Tape transmitter. As described in Specification 197,633, the contact 30, Fig. 1, is closed at every upward movement of the striker bar 9', at an instant determined by the setting of the adjustable projection 30<a>, and a current is sent through the winding 12 of the transmitter relay TR. If a space 4<c>, Fig. 1<a>, is being signalled, neither of the feelers 5, 6 can rise, and consequently the contacts 7, 8 remain open and the coils 10, 11 are idle. In response to the coil 12 the armature 14 is set to the right, sending a full period negative impulse (- -) to line. If a dash, 4b, is being signalled the feeler 5 rises and current passes through contacts 30, 8, and coil 11 so as to overpower the effect of coil 12 : the armature 14 is set to the left and a full-period positive impulse (+ +) is sent to line. If a dot, 4a, is being signalled, feeler 6 rises and current passes through coil 10 so as to overpower the effect of coil 12 and to send a positive impulse to line, the condenser K1 meanwhile acquiring a charge; but when contact is broken at 7 at the end of a half-period the condenser K, discharges through the coil 10, moves the armature 14, and so reverses the current in the line for the second half of the period, the complete impulse having the form (+ -). Retransmitter. In the apparatus shown in Fig. 2, four segments in each distributor ring correspond to one complete signal period. If the dot relay CDR1 and dash relay CDR2 of a cablecode receiver be both idle, so that a space signal is being received, the brush b3 on passing over a conducting segment of the spacing ring RD2 energizes the coil 204 and, the coils 205, 206, being idle, sets the armature 211 to the right so that the line relay 209 is actuated to send a fullperiod negative impulse to the outgoing line L2: the condenser K2 discharges, when the brush b3 breaks contact. through its shunt resistances r2 without affecting the line relay. If a dash is being received the dash relay CDR2 gives positive to the conducting segments of the dash ring 203. and an impulse passes through the brush b, to the coil 206, which overpowers the coil 204 and sets the armature 211 to the left, causing a fullperiod positive impulse (+ +) to be sent to the line. L2. If a dot is being received. the dot relay CDR1 gives positive to alternate conducting segments in the dot ring 202. When the brush b<4> passes over one of these live segments an impulse is cent through the condenser K3 and coil 205. which overpowers the coil 204 and causes a nositive impulse to be sent to line: but after the lapse of half a period the condenser K3 is discharged through the coil 205, on the brush b4 reaching the next conducting segment, and the direction of the line current is consequently reversed for the second half of the period, so that a dot signal (+ -) is sent to the line L2. The current strengths in the coils 204. 205, 206 may be regulated by making the capacities of the condensers' K3. K4. each three times as great as that of condenser K2. A coil 207 provides a locking bias to hold the armature 211 against either contact. Receiver. Each signal consists of two halves represented by (+ -) for a dot, (+ +) for a dash. or (- -) for a space. the first being a selecting half and the second a signalling half. The brush h<1> at the receiver B passes downwards over four distributor segments during the period of one impulse, the odd-numbered and evennumbered conducting segments corresponding respectively to tne selecting and signalling halves of the impulse. If a space signal is being received, the negative selecting halt of the impulse, relayed through armature 16 of the line relay MR, an odd-numbered segment of ring 17<1>, brush b<1>, and coil 18 of selecting relay, sets the armature 40 to the right, and the signalling half of the impulse consequently passes through the next even-numbered segment of ring 17<1> to the relays 28, 22, 21, setting the armatures 41, 42, both to the left, so that the recorder 24 is shortcircuited and records a space. If a dash or a dot is being received the selecting half of the impulse is positive : the armature 40 is therefore set to the left, and the signalling half of the impulse is positive : the armature 40 is therefore so wound that the negative half-impulse which completes a dot sets the armatures 41, 42 to their inward positions and so sends a positive current through the recorder 24, while the positive halfimpulse which completes a dash moves these armatures 41, 42 outwards and so sends a negative current through the recorder. Synchronizing apparatus. The line signals also pass through the corrector relay 26, and the brush b2 is so related to the brush b1 that normally it lies on an insulating segment of the ring 25<1> during the receipt of a signal, in which case every rightward movement of armature 56 causes the break relay 54 to disable the make relay 55. If. however, a signal moves armature 56 to the right when brush b2 is on a conducting segment, current passes through the brush to the make relay 55 before this circuit has been broken at 54<1>, and consequently the mechanical correcting magnet 57 is actuated to apply a phase correction. Further, if the phase error be so great that the selecting halves of the impulses fall on the even instead of the odd segments of the Ting 17<1>, a negative half-impulse will occasionally be followed by a positive half-impulse. The former will move the armature 40 to the right, while the latter will energize the relay 23, which is responsive to positive but not to negative impulses, and will effect a correction through the make relay 55. Transmission of synchronizing impulses. The modification shown in Fig. 3 is so arranged that when the tape has run out, synchronizing impulses of the form shown in Fig. 3a (AAA followed by fourteen spaces) are emitted from the sending station. The end of the lever 311, Fig. 5, is, in the absence of the tape 4, able to pass up into grooves in the tape-roller 320, and contact 312 therefore remains closed. The required signals are then sent out under the control of the contact 30 which intermittently energizes coil 12, and of the contacts 7, 8, which intermittently energize the coil 10, 11, provided that the armatures 317, 318 be closed. These armatures are controlled by biasing coils 301, 304, which tend to close them, and by opposed energizing coils 301, 302, which are permanently in circuit, so long as the contact 312 is closed. When the contact 306 is so positioned by the cam 305 as to short-circuit coil 301 or coil 302, contacts 317 or contact 318 is closed by the weaker biassing coil 305 or 304 as the case may be, and a dot or a dash is sent to line as described in connection with Fig. 1. When the contact 306 is in its middle position both contacts 317, 318 are open, and spaces are sent to line.