Patent GB-574349-A (GB)
Title: Improvements in printing telegraphs
IPC: H04L21/00
Filed: 1941-01-17
Abstract: 574,349. Facsimile telegraph apparatus. EVANS. G. T., MORRELL, F. O., and FINLASON, W. E. Jan. 17, 1941, No. 686. [Class 40 (iii)] A facsimile telegraph transmitter comprises a keyboard having a number of static contacts corresponding to the number of elemental areas into which the characters to be transmitted are divided, a number of key-operated key-bars, each cut or shaped to select the particular contacts corresponding to the particular character on the key, and a distributer for connecting the selected contacts in regular sequence to the transmission line. As shown, the fixed contacts are in the form of wires b, Figs. 2 and 4, stretched transversely in notches in insulator strips b<1> under the key-bars a<1> fitted with the keys a. Each key-bar is formed with projections a<3> adapted to make contact with the wires b according to the code used. The code may be that shown in Fig. 1 in which the space occupied by each character is divided into five vertical lines comprising five elemental areas each, twenty-five elemental areas in all. For this code, the key-bar for the character H comprises five teeth a' as shown for the left key-bar on Fig. 2. The end teeth of this key-bar are long and will make contact with five wires to send signals corresponding to the two vertical lines of the character H. The three middle teeth are narrow ones and will each make contact with one wire only to send signals corresponding to the middle horizontal line of the character H. The other characters are analysed in a similar manner. These signals are sent through a distributer comprising fixed contacts b<2> connected to the wires b and a rotating brush b<3>. The distributer shown includes a number of idle contacts b<5> for spacing and a number of contacts b' for start-stop signals. The receiver comprises a similar distributer driven in synchronism and is described in Specification 574,350. To prevent irregular signals, the depression of a key is made to lock the other keys against depression, and all the keys are locked in their positions until the distributer has completed its revolution. For these purposes, a bar e<9> extends across the keyboard under the front ends a<11> of the key-bars and is fitted with end trunnions. When a key is depressed, the end a<11> of the corresponding key-bar bears on a lip e<12> on the bar e<9> and rocks the bar on its trunnions, thereby causing another lip e<99> of the bar e<9> to engage over the end a<11> of the depressed key-bar and under the ends a<11> of the undepressed key-bars to prevent their displacement. At the same time, a rod e<5> connected by a pivot to a bracket on the bar e<9> is pulled out, and a finger e<4>, Fig. 8, at its inner end deflect s a lever e<3> which releases a one-revolution clutch device e for the signal distributer. As soon as this distributer begins its rotation, a cam thereon rocks a lever e<7>, and the end e<77> of this lever locks the rod e <5> in its forward position ; and this in turn causes the bar e<9> to hold the key-bars in their positions. At the end of the revolution of the signal distributer, the lever e<7> is released, and the several parts return to normal position in readiness for the next operation. The transmitter is shown in combination with the receiver described in Specification 574,350. The circuit of the combined apparatus is shown diagrammatically in Fig. 2. If a signal arrives from a calling station by the line c, d, a relay k<1> is energized and closes a contact k<2>, thereby setting a buzzer k in operation. The motor O is started for transmission or reception by the closing of a switch n'. This switch n<1> is associated with switches n<2>, n<3>, n<4> so that when the switch n<1> is closed the switch n<2> opens and breaks the circuit of the buzzer k, the switch n<3> opens to cut off the relay k<1>, and the switch n<4> closes to connect the receiver in circuit. The normal practice will be to record locally the message transmitted to serve as a check. To cause the receiver to operate during local recording in similar condition as in reception from a distant transmission, a resistance l' is then inserted in the circuit of the receiver by the opening of a switch l by a cam on the shaft of the signal distributer.