Patent GB-391223-A (GB)
Title: Improvements in or relating to telegraph systems
IPC: H04L1/14
Filed: 1931-10-23
Abstract: 391,223. Type-printing telegraphy. CREED & CO., Ltd. and GRIFFITH, R. G., Telegraph House, Croydon. Oct. 23,1931, No. 29444. [Class 40 (iii).] Each signal is automatically checked or repeated back by the receiving station to the transmitting station, and means are provided to prevent the checking signals from disturbing the ordinary signals. Circuits. Fig. 1 shows a d.c. station used for simplex traffic but arranged like a differential duplex station. During reception the switch 11 is automatically set to the left so that the line is connected to a retransmitting contact 14 which checks back the received signals under the control of apparatus described below. During transmission, however, this connection is broken, the switch contact 4 being set to the left by the transmitter during the normal emission of signals by contact 7 and for a short interval thereafter. At the sending station, therefore, the checked-back signals operate the receiver R which prints them for monitoring purposes. In an a.c. station, Fig. 2, one frequency is used for sending and another for checking back. When the station is receiving, as shown, the received signals pass through filter 26 and amplifier 31 to receiver R, which controls the sending back of checking signals by contact 14. The checking signals are sent by generator 22 through transformer 25, and the retransmitter contact 14 is opened to produce a signal impulse by unshort-circuiting the generator. The outgoing checking signals are prevented by filter 26 from reaching the local receiver R. When the station is transmitting, however, switch 30 substitutes filter 27 for filter 26, so that signals of checking frequency are now admitted to receiver R ; switch 23 is opened to change the frequency of the generator from the checking to the transmitting frequency ; and switch 11 is closed so as to disable the retransmitter contact 14. Signals are now sent by transmitter contact 7. In a modification, Fig. 3 (not shown), suitable for multi-channel voice-frequency signalling, two separate oscillators of different frequencies are employed ; at the receiving station a different relay is operated through each of the networks 26, 27, and a single final relay is controlled alternatively by these two. Printer and retransmitter for checking back received signals. The armature 40, Fig. 4, of the receiver magnet controls a start-stop clutch 41 for rotating shaft.43 and also sets the notched bar 42 to one or other of two positions in accordance with the polarity of the received impulses. Keyed to shaft 43 are five pairs of cam discs 45 .. 49 which control the printer and also the retransmitter. Each pair of discs, when its cams 52, 53 reach the gate 54 in the common notched bar 42, is set to one or other of two axial positions, according to the position of the bar at that moment. The pair of discs is thereafter locked against axial movement by engagement of their associated flange 55 in a groove in bar 56. The discs operate the combiner discs of the local printer, and also effect the retransmission of checking signals, their cams 52, 53 serving to displace a common notched bar 61 for this purpose. Start and stop signals are retransmitted by a sixth pair of cam discs 63.