Patent GB-861249-A (GB)
Title: Improvements in or relating to telegraph transmission systems
IPC: H04L12/00
Filed: 1957-06-21
Abstract: 861,249. Code telegraphy. SIEMENS & HALSKE A. G. June 21, 1957 [June 21, 1956], No. 19696/57. Class 40(3) In a telegraph transmission system, a voicefrequency generator located in a subscriber's loop is frequency-modulated by a telegraph transmitter at the subscriber's set without the interposition of a relay or relays, and the resulting frequency-modulated voice frequency signals are transmitted to a telegraph receiver without the interposition of a relay or relays. The circuit arrangement, Fig. 2, of a subscriber comprises the receiving magnet EM of a teleprinter having its transmitting contact sk connected in the circuit of a voicefrequency generator S normally connected at a1 and generating a frequency fs when a power supply unit NGS is connected whilst the receiver limiter BE is connected over contact a3 in the position shown to a section of the filter FW responsive to the frequency fe to which all receivers, normally in operative condition through a power unit NGE are tuned in the rest or non calling state of the system. On the initiation of a call, the operation of a key closing contacts ATI energizes a relay A which at contact a5 connects the unit NGS and at contact a2 changes the frequency of S to fe which is passed over contact a1 via section fe of the filter to the line a/b. At the receiving station the frequency fe is passed via the section fe of the filter FW to limiter BE operating relay B which at contact b1 connects the units NGS to the transmitter and at a contact (not shown) switches in his teleprinter. Also the transmission of the frequency fs from the called subscriber passes at the calling station over operated contact a3 and limiter BE to operate relay B which starts the teleprinter of the calling subscriber, and information transmitted from the called subscriber passes over operated contact a4 to the section of the discriminator D tuned to the frequency fs. At the called station the information passes over dial contact nsi1 bridging capacitor Cn filter section fe, contact a3 (unoperated), over contact a4 (unoperated) to the section of the discriminator D tuned to the voice frequency fe, and via amplifier V to the magnet EM of the teleprinter. At the end of transmission from the calling station the normal frequency fe is discontinued for a predetermined period so that relay B at the distant station is de-energized and at opened contact b1 disconnects the unit NGS. At a contact (not shown) the motor is stopped. The discontinuance of the frequency fs from the called station effects the release of the relay B at the calling station which at a contact (not shown) opens the driving circuit of the motor at that station which is returned to the rest condition by the release of the key ATI and the consequent de-energization of relay A. Fig. 3 (not shown) comprises a diagrammatic arrangement of subscriber stations, as represented by Fig. 2, connected to exchanges linked by a trunk line having a number of channels. Frequency changers provided at each end of the trunk line transpose the modulated frequencies of connected calling subscribers to different frequencies associated with the available channels, and at the exchange connected to the called subscribers, the trunk line frequencies are reconverted to the receiving frequencies of the subscribers of that exchange.