Patent GB-333556-A (GB)
Title: Method of and apparatus for operating cable telegraph systems
IPC: H04L25/49
Filed: 1929-05-07
Abstract: 333,556. Western Union Telegraph Co. March 30, 1929, [Convention date]. Type-printing telegraphy; restoring or modifying imperfect signals. - A marking or selecting signal element is denoted differentially, i.e. by a change of polarity in the line-current while a spacing or non-selecting element is denoted by a continuance of polarity. Signals composed of equal + and - elements according to this code may be distorted by the line into combinations of + - and zero elements but reconverted into Baudot code by the zero elements being treated as marks and the + and - elements as spaces, the need for a Gulstad or like interpolators for lost impulses being thus avoided. The signal periods may be of non-uniform length; alternatively the marks may be two, three or more times as long as the spaces and the fundamental signal-frequency is thus reduced. Line and instrument faults produce errors of synchronism which are detected by the misprinting to which they give rise and are corrected manually step by step. Transmitter for differential non-uniform code. According to one code, marks are twice as long as spaces and are denoted differentially, i.e. by changes of polarity; thus the letter A punched on a tape according to the ordinary code as (++ - - -), Fig. 4 (a), is transmitted when following a (+) impulse as (- - + +, +, +, +) Fig. 4 (b), and the latter combination can be signalled at a higher message-speed without blurring, Fig. 4 (c). The contacts t1, t2, Fig. 2, are in this case set to the marking bar MB, and the contacts t3, t4, t5 to the spacing bar SB, by a tape punched in the ordinary code for the letter A. For each space (t3, t4, t5) the fork-tine ft makes one to-and-fro vibration; each contact at 13 energizes relay 15, so as to rotate the distributing cam-shaft RC; and establish contacts at C3, C4, C5 in succession; and each contact at 12 is without effect on the line relay R4, since battery negative is applied at both emds N, SB, of the circuit that runs through relay R3 and contact C3, C4, C5. Thus the relays R1, R2, R3 and unaffected and the outgoing space signals are of unit length and comprise continuances of the existing line polarity. For each of the first two contacts t1, t2, however, the duration of the signal is doubled and the polarity of the line is changed, to denote a mark. At the end of the preceding signal-element, fork-contact at 13 energizes the relay 15 and rotates the shaft RC one. step, so as to establish contact at C1. At the same time the lower (restoring) winding of relay R1 is energized in parallel, and armature t1 is set to the left if not already in that position. The ensuing fork-contact at 12 makes a circuit from MB to N via t1, 01, r1 and lower (energizing) windings of relays R2, R3 so that armatures r2, r3, are moved to the right. The effect of the movement of armature r2 is that the next contact at 13 fails to energize the stepping magnet 15; instead, the circuit is diverted by armature r2 to the upper winding of the relay R1 so as to move armature r1 to the right in readiness for restoring the armatures r2, r3. Thus, for marking signals the duration of the signal element is doubled while the right-ward movement of armature r3 causes condenser K to discharge through line relay R4 so as to reverse the position of armature r4 and change the polarity of the line current. Since the condenser K is charged in parallel with the line, successive discharges of the condenser will alternate in sign, and the armature r4 will alternate in position. The second time that contact is made at 12, the upper (restoring) windings of relays R2, R3, are energized, while at the next contact at 13 the lower (restoring) winding of relay R1 is energized; this contact at 13, therefore, operates the stepping magnet 15 to begin a fresh cycle of operations. The sixth distributor contact 14 operates the tape-feed magnet 23. In a simplified form of the apparatus a specially punched type may be employed instead of the Baudot tape used in Fig. 2. In the modified tape the duration of the signals is determined by the spacing of the tape-holes, which are arranged longitudinally; and the magnet R3, Fig. 2 (RR, Fig. 6, not shown) is directly controlled by this tape. Receiver for differential non-uniform code. The signal for letter A, sent as above, arrives in the form shown in Fig. 3F but is passed to the receiver through the condenser K2 in the form shown at, 3G. At every change of polarity (denoting a mark) the relay R6, controlled by the line relay, sends ran impulse through the condenser K2 and momentarily energizes relay R7 or R8, closin, a circuit through one of the printer magnets PR, selected by that one of the contacts C1 - - C5 which is closed at the moment, through contact r7 or r8 and contacts r1 and 12<1>. Relay R<1>2 is thus energized and cuts off the stepping magnet 15<1> so as to double the duration of the signal period in the manner described in connection with the transmitter. When no change of line-polarity occurs on the other hand, the circuit through the printer PR and relay R<1>2 is broken at r7, r8, the printer registers a space-element, and a signal period of unit length is determined. The relay R<1>3 serves for retransmission. Transmitter for differential uniform code. Figs. 8, 9, 10 illustrate the use of a code in which marks and spaces are denoted differentially, i.e. by changes and persistences of polarity respectively, the signal periods being of uniform length. The need for a Gulstad or like interpolator of lost impulses is obviated by this arrangement. The ordinary Baudot code (a), Fig. 8, would be distorted, by the cable to the form (b); but according to the invention the signals (a) are transformed to the form (a) before emission. Thus the rotor RC, Fig. 9, is moved one step each time the fork-contact 13 is closed; and each time the fork-contact 12 is closed the relay R3 is energized or not according as that one of the tape-controlled contacts t1 - - t5, which is accessible via one of the contacts C1 - - C5, is on the marking bar MB or on the spacing bar SB. When the relay R3 is momentarily energized against the bias of the circuit BS, condenser K discharges through relay R4 so as to reverse the polarity of the line. In a modification, Fig. 10, the tape-controlled contact t2, for example, connects the marking bar MB or spacing bar SB, as the case may be, to its associated contact 2 on the distributor B via one or other pair of relay windings w, w, or w1, w1, according to the position in which the armature t1 was set under the control of the contact t1. If contacts t1, t2 have been set to the same bar MB or SB the armature r2 does not move, but if the contacts t1, t2 are oppositely set a change of polarity is sent to line via contact 2A of distributor B1. Receiver for differential uniform code. Signals transmitted as at (c), Fig. 8, are distorted by the cable to the form (d), but are reconverted to the ordinary Baudot form (e), indentical with (a), by the receiver, which treats zero elements as marks and + and - elements as spaces, the zero elements having been produced by changes of polarity at the transmitter. To this end the receiver relay NL, Fig. 10, is so connected that when its arm t is central the circuit of one of the printer magnets PR is completed via the distributor D and armature op, but when a current of either polarity is received the magnet OP is energized and the printer-magnet circuits are broken at op. Synchronous movements.-The receiver fork N' Fig. 2, is synchronized with the transmitter fork N by the impulse sent through condenser K1 at each change of polarity in the line signals. When the tape has run out, synchronizing signals are automatically transmitted, since all contacts t1 - - t5 are set to the marking bar MB, Fig. 2, and therefore effect reversals of the polarity of the line. In case the receiver should be out of phase with the transmitter, however, a message may start with a series of signal groups denoting a " space," which is (- - + - -) in ordinary code, so that according to the present code, Fig. 5<a>, the polarity is reversed before the third element of each group. The stepping magnet 15, Fig. 5, receives a momentary + at r3 at each change of polarity in the line, and so steps the rotor RC one step for each signal group until the phase has been corrected, i.e. until the change of polarity occurs when contact C3 is closed. Magnet R4 is then energized and holds on, giving + at r4 to the stepping magnet 15, which thereafter maintains the correct phase by acting one for each signal element. If misprinting, due to phase errors, should be observed, the receiver stepping magnet 15<1>, Fig. 2, may be cut out for one signal-element-period at a time by the manual operation of a key (Fig. 11, not shown), an arrangement of relays and condensers ensuring that only one step shall be lost for each operation of the key. The latter operation is repeated until misprinting ceases. Break-in signals. A service message may be interposed in the middle of an ordinary message without disturbance of the paging. The received signals operate the ordinary printer A, Fig. 7, until the all-blank signal is received; the signals are then diverted by the armature f to the service-message printer B until the further all-blank signal arrives, when the signals revert to the ordinary printer A. The contacts Z1, associated with the printing- magnet PM of printer A, are closed for each letter-signal but are open for the all-blank signal. The current-impulse through the contact C6 then operates the relay D, which is no longer shunted by the printing-magnet, so that the condenser K discharges through xelay 'F, whose armature f cuts out printer A and cuts in printer B; the condenser-discharge also passes through relay E whose armature e reverses the polarity of the charge applied to the condenser through the spring-returned armature d. Mu