Patent GB-248798-A (GB)
Title: Improvements relating to telephony and telegraphy
IPC: H04M11/06
Filed: 1924-09-11
Abstract: 248,798. Joly, P. Sept. 11, 1924. Duplex telegraphs.-Telephone subscribers are enabled to telegraph to each other over the usual cord circuits of a common battery exchange system by means of impulses which induce currents over the usual condensers, transformers &c., in a secondary circuit connected to a two-way repeating arrangement called a telemixte. The Spedfication describes a number of telemixtes for simplex and duplex working and a number of substation arrangements, some of which are designed to enable a subscriber to receive a telegraph message in his absence. Several telemixtes in cascade may be used and thermionic amplifiers may be included between the outgoing end of a cord circuit and the telemixte. A lay out of the system is shown in Fig. 1. A substation 1 sends telegraph impulses over the exchange apparatus 3. Currents induced in the line 4 control a repeating relay 6 through a differential transformer 5. The repeated impulse is without affect on the other repeating relay 6 bis since the current affects both primary windings of transformer 5 bis to an equal extent, the line 4 bis &c. being balanced by an artificial line 7 bis. The messages exchanged may be recorded at the telemixte by apparatus connected between the common pole of the batteries 9, 10 and the respective artificial lines 7, 7 bis. Modified telemixtes. The primary windings of transformer 5 may be split as shown in Fig. 6 or two transformers may be used, Fig. 8, or differential relays 23, Fig. 10 may be used without transformers. Further arrangements are described the object of which is to feed one or both of the lines normally with current from a battery in the telemixte. In a further arrangement, Fig. 17, no artificial lines are employed. Further simplex arrangements are described in which the differential transformers of a duplex arrangement control a single relay, and in which a single differential relay is employed. Substation arrangements. As shown in Fig. 20, incoming signals control a relay 33 which, owing to the arrangement of the artificial line 34 and differential transformer 5, is unaffected by the operation of the transmitting contact 31. Transmitted messages however affect a relay 32 for producing a local record. The station works duplex if the relay 32 is made to control a separate recording instrument. Modified systems are described in which the differential transformer is replaced by two transformers, and in which no transformer is provided, signals being received. direct by a differential relay. In the above arrangement it is necessary to have a local battery for feeding the signal-recording apparatus 35. In a further modification, Fig. 26, current for feeding the signal recording apparatus 204 is derived from the exchange battery. With this arrangement it is necessary to keep the steady line current constant irrespective of the position of the receiving relay 203. Accordingly an impedance 207 equivalent to the apparatus 204 is provided and relays 208, 209 are arranged as shown or in series with the apparatus 204, 207. The effect of this is that the line is always bridged by the same impedance, 204, 208 or 207, 209 according to the position of the receiving relay 203. Signals are transmitted by the contact 205. Sparking preventing. The receiving relay 11, Figs. 3 and 4, controls the signal recording apparatus 12 by means of a circuit comprising resistances 13, 15 and a condenser 14 or by means of an arrangement comprising equal resistances 17 and equal batteries 18, 19. Resistances 8, Fig. 1, prevents sparking at the contacts of relay 6. Starting and stopping arrangements. In systems without provision for recording messages in the subscriber's absence the substation comprises in addition to the apparatus described above, a two or three-position switch for connecting up at will the transmitting and receiving apparatus. The switch is arranged in one position to energize a relay which locks itself up, starts the motor of, and completes circuits for the telegraph apparatus. The circuits closed by this relay may be made directly by the key. Fig. 29 shows a system in which the recording magnet 204 is fed from the exchange battery, the arrangement being substantially the same as that shown in Fig. 26, relay 209 however being omitted. With the key in the mid-position, shown the apparatus is canable of receiving a message in the absence of the subscriber. With the key in the left hand position the station is an ordinary telephone station and ringing current affects the bell 213 or, if the telegraph apparatus is running, a transmitting telegraph station. The telegraph apparatus is started by energizing momentarily a relay 216. This is effected by throwing the key to the right or, if the key is in the mid-position, by means of incoming ringing current. Relay 216 energizes relay 217 which locks up in series with relay 218 when 216 falls back. The motor 215 starts up and assuming the key is in the " receive " position the line wires are connected together over 222, 202, 220, 207, 203, 205, 219, 204, 206. Relays 219, 222 pull up and respectively open a point in the circuit of the receiving relay 221 and complete the circuit of the receiving relay 203. Relay 219 is slow to release and remains energized during a message. The termination of the message has the effect of throwing relay 203 permanently. on to its right hand contact, whereupon relay 219 falls back and relay 220 which is too sluggish to be energized when its circuit is made momentarily by the signal impulses, pulls up and energizes the re-setting relay 221 which brings relay 203 back to the contact shown and unlocks relays 217, 218 whereupon relays 220, 222 and finally 221 fall back to complete the restoration to normal. Resetting may be effected at the station itself by the opening of key 223 or by a key (not shown) for energizing relay 221 or by operation of the hook switch 210. The system shown in Fig. 25 is similar, but the telegraph apparatus 114 is fed from the local battery 111. The apparatus is set into action when the relay 118 is energized either by means of the key 107 bis or by incoming ringing current. Relays 108 bis, ter, are locked energized when relay 118 falls back, the motor 109 is started, and the line wires are bridged through the relay 121 and a primary of the receiving trarsfonner (not shown). Relay 119, pulls up over 114, 113, 112 and disconnects the re-setting relay 120. Relay 121 after an interval connects up the receiving relay 115 to the secondary of the transformer. The return of the system to normal takes place automatically at the end of a message because relay 115 then stays on its right hand contact long enough to release relay 119 and energize relay 120 which unlocks relays 108 bis, ter. This produces a current impulse which restores relay 115, and after a further interval relay 121 falls back to break the circuit of relay 115. Specification 25362/99 is referred to.