Patent GB-384691-A (GB)
Title: Improvements relating to telegraph signalling apparatus
IPC: H04L5/22
Filed: 1931-07-08
Abstract: 384,691. Code telegraphy. IMPERIAL & INTERNATIONAL COMMUNICATIONS, Ltd. and HIGGITT, H. V., Electra House, Moorgate, London. July 8, 1931, No. 19694. [Class 40 (iii).]. In double-current cable-code signalling, the dot-transmitting and dash-transmitting con. tacts become effective alternately. Multiplex distributers of the cam or of the rotary type may be employed. In the transmitters TA, TB, a dot is + +, a dash --, and a space OO, but in the line L a dot is ( + +), a dash (--), and a space ( +-), as described in Specifications 267,180 and 294,715, [both in Class 40 (iii), Telegraphs, Electric]. Transmitter TA, Fig. 9, operates half a signal period ahead of transmitter TB; thus line A, Fig. 11, represents letter A sent by transmitter TA, and line B represents letter B sent concurrently by transmitter TB. The dot armatures 7, 9 of both transmitters when not operated rest on negative back contacts 11, 13, but when operated they abut on positive front contacts 15, 17 ; and the dash armatures 8, 10 are similarly arranged but with reverse polarities..The dot armatures 7, 9 are connected to contacts 25, 26 of a mechanical switch 19 which provides access to the dot levers alternately for half a period each, the phases of the switch-operation being shown by the lines A19, Fig. 13, for channel A and lines B19 for channel B. Similarly the dash levers 8, 10 are connected to contacts 27, 28 of a switch 20 which makes contact for alternate periods as shown at A20 and B20. Thus the dot contact-period for channel A overlaps the dash contact-period of the same channel by a quarter of a signal-period, the pair of contactperiods being followed by an empty quarter of a signal-period, and the arrangements for channel B are similar but in opposite phase. The tongues of switches 19, 20 are connected to contacts 33, 34 of a mechanically operated switch 35, whose tongue feeds the line L and makes alternate contacts represented by lines 3519 and 3520, Fig. 14. Switch 35 divides the line time evenly between dots and dashes, while switch 19 divides the time allotted to dots evenly between the two channels A, B, and switch 20 similarly divides the dash time between the channels. The result is that alternate half periods of line time are allotted to channels A, B, as shown at L, Fig. 15. The contact-periods of the switches, shown in Figs. 11-14, are also shown by the circular arrows in Fig. 9. When spaces are being transmitted on both channels, the line L is connected for successive quarter-periods to the four back contacts, the two transmitters TA, TB in turn, and space signals as shown at 63, Fig. 15, are sent to line. When a dot signal is sent, for instance by transmitter TA as at 50, Fig. 11, it appears in the line L as at 61, 62, the first half 61 of the line signal being sent by the back contact of dash relay 8, as in the case of a space, while the second half 62 is sent by the dot relay 7 which has access to the line for the corresponding quarter-period. When a dash signal is sent, for instance by transmitter TB as at 54, Fig. 12, it appears in the line as at 85, 86, the first half 85 being sent by dash relay 10, which has access to the line for the corresponding quarter-period, while the second half is sent by the back contact of dot relay 9, as in the case of a space. Instead of selecting one half or other of a divided battery SB, the contacts may select one coil or other of a differential line-relay, Fig. 10 (not shown) ; and in a further modification the mechanicallyoperated switches 19, 20, 35 are replaced by a rotary distributer, Fig. 18 (not shown). Monitoring receivers are connected to the line L through contacts R, Fig. 9, which open for the periods indicated by the short lines RA, RB, Fig. 16. The monitor records in the two channels are in the form shown at ra, rb, Fig. 17, dots being denoted by large positive indentations as at 69, 70, and dashes by large negative indentations as at 71, 72. Spaces are indicated by the absence or smallness of the indentations, such as 66, corresponding to them, since they are communicated to the receivers at the moment when polarity is being reversed at their middle points. At the receiving end of the line, the channels may be separated by means of the apparatus described in Specification 386,784 or according to the Provisional Specification 328,945, [Class 40 (iii), Telegraphs, Electric].