Patent GB-442891-A (GB)
Title: Improvements in or relating to printing telegraph systems and apparatus
IPC: H04L17/00
Filed: 1934-08-17
Abstract: 442,891. Type-printing telegraphy. CREED & CO., Ltd., and SALMON, R. D., Telegraph House, Croydon. Aug. 17, 1934, No. 23795. [Class 40 (iii)] Errors in the transmission of messages by a 5-unit code are rendered obvious by the use of a code which makes the errors cumulative. Code. The message is originated in the ordinary Baudot code, but each character is signalled as a group of impulses which indicate the difference between that character and the preceding character. For instance, if the first Baudot element in the character to be signalled is the same as the first Baudot element in the preceding character, a space is sent as the first impulse in the transmitted group ; but if not, a mark is sent. Thus the group denoting each character depends on the previous character, and errors are cumulative. Transmitter, Fig. 2. Five combination bars 16 are moved to right or left by the key 4 and remain in that position until reset by depression of another key. When a bar 16 moves in either direction-i.e. when its setting is other for the character to be signalled than for the preceding character-it trips a latch 5 through an interponent 14 and so rocks a selector lever 7 which is adapted to hold the top of one or other of two levers 10 so that a shuttle 11 may be actuated by a cam 9 for controlling the emission to line of one of the five impulses. The selector levers 7 are reset by a cam-actuated bar 6 after the transmission of each character. Receiver using combiner combs, Fig. 3. Each of the five combiner combs 22A remains in the position to which it was set for the preceding character, unless it is reset by its cam 1A being released and performing half a revolution ; this occurs when a marking impulse is received. The received impulses control the magnet armature 36 and so the selector lever 37, which holds or fails to hold the top of a cam lever 35. Consequently a cam 38 moves or fails to move the transfer bar 40 to the left and so releases or fails to release the cam-shaft 1 for the purpose of changing the setting of the corresponding combiner comb 22A. Receiver comprising differentially geared typewheel, Fig. 6. In this embodiment the typewheel (not shown), is set as described in Specification 436,296, through five epicyclic gears which impart to it ¢  #, <1>/16 and <1>/32 of a revolution respectively. Each gear has a planet-wheel frame 6c which is moved to one or other of its two settings at each half-revolution of the clutch 6a. This clutch is released or not, during each signal period, according as the corresponding impulse is a mark or a space. To this end the impulse sets a selector lever 37 and so through cam 38 and levers 35 sets a transfer bar 1d to the left for a spacing impulse or to the right for a marking impulse. Only in the latter instance does the striker 1b engage the distance piece 44 so as to actuate the levers 45, 46 and release the halfrevolution clutch 6a, setting the corresponding planet-wheel frame 6c to a position different from that which it had for the previous character. Transmission of unison signal. For automatically sending an all-blank unison signal as soon as signalling has ceased for a given time, a system of relays, Fig. 5, may be provided. A delay-action switch closes contact S1, when signalling has ceased for one second, and so pulls up the sluggish relay H. Through contact H1 a magnet M pulls up and actuates an allblank key 3 Fig. 2 (not shown) for resetting all combination bars 16 at the transmitter into their spacing positions. Through contact H2 a sluggish relay N pulls up, connects spacing battery to line at N1, and closes at N2 the circuit of a sluggish relay O which at O1 cuts out the relay H and restores the status quo. Unison devices at receiving station. For setting transmitter and receiver into unison when an error in transmission has occurred, a unison signal comprising five spacing elements is sent repeatedly to line. This eventually has the effect of setting all the receiver combs to the spacing position. At the receiver shown in Fig. 3 a cam 53 is provided which rotates a little slower than the cam 38. During a message, the cams are stopped at the end of each signal period and so keep substantially in phase with one another, but during the receipt of the unison signals they rotate continuously and fall out of phase, Fig. 4 (not shown). Now, during each revolution, a depression 24, Fig. 4 (not shown) on the cam 38 permits a frame 57 to rise, and this frame carries five rockers 59 each bearing two peckers 16, 21. Where a comb lever 22 is in its lower position so as to engage a pecker 21, the pecker 56 will rise; and this pecker is pushed to the left during each revolution by cam 53 acting through bell-crank 54. Normally the latter action occurs before the rising of the pecker, but during the receipt of unison signals, when the cams 38, 53 have become sufficiently out of phase the pecker 56 catches a projection 40A during its leftward movement and so moves the bar 40 to the left and causes the comb 22A to be set to its upper position through release of the cam 1A. But where a comb 22A is already in its upper position this action does not take place, since the spring 20 tilts the rocker 59 and prevents the pecker 16 from rising. Thus eventually all the combs are set to their upper positions in correspondence with the all-space unison signal. In the receiver shown in Fig. 6 an analogous arrangement is adopted. A cam 68 is tripped by a lever 67 at each revolution of the shaft of the main cam 38, and acts in conjunction with cam 68 (if the corresponding epicyclic gear is in the marking position) and levers 69, 61 to move the distance pieces 44 to the left. Normally this has no other effect, the cams being so timed that the distance pieces 44 have returned to the position shown by the time that the striker 1b acts ; but when the cams 38, 68 fall out of phase under the influence of the unison signals, the result is that the clutches 6a return to their spacing positions.