Patent GB-449609-A (GB)
Title: Loud-speaking and amplified telephone systems
IPC: H04B3/20
Filed: 1934-12-24
Abstract: 449,609. Direct-call and automatic exchange systems. TELEPHONE PRIVE NATIONAL, 13, Rue Delambre, Paris. Dec. 24, 1934, Nos. 36952, 36953, and 36954. Convention dates, Dec. 30, 1933, Dec. 30, 1933, and Aug. 3, 1934. [Class 40 (iv)] In a telephone system employing amplifiers and loud-speakers with voice-operated means for controlling the operation of the amplifiers in accordance with the direction of speech, each sub-station is provided with a key by means of which control of the system, independent of the voice-control, may be obtained at any time. The invention is described with reference to two-station direct-call systems and to an automatic exchange in which the amplifiers are associated with finder-connector links. Direct-call systems, Fig. 1. When subscriber St presses call-button a, battery is connected to amplifiers AM1, AM2 and the sound of buzzer Ro is transmitted by microphone M to loudspeaker IHP. During speech from St to ISt, relay C operates cutting out resistance af3 and opening the output circuit of amplifier AM2. Subscriber ISt may break in by operating key Ii which bridges the open contact of relay C. At the end of conversation the operation of key d restores contact a1 which remained closed after a was released. In a modification, red, green, and white lamps at each station are controlled by relays C, IC to indicate the condition of the system at any time. Automatic exchange systems, Fig. 3 ; callfinder CA. The operation of calling key ar partially operates relay A over its lower winding in series with the left-hand winding of relay Y. Interrupter EI operates call-finder magnet CA and when the line is found, relay T operates over wiper c of the final selector SU in its normal position, wiper c of CA, upper winding of A, and key dr. Relay B operates and locks in series with magnet CA, and relay A now operates all its contacts, lighting red lamp R to give a dialling signal, and extending the dialling loop over wipers d, e to both windings of Y. Final selector SU. Impulses are repeated by relay Y to magnet SU in series with relay J which short-circuits its left-hand winding, and releases T. At the end of the digit when J releases, relay U operates, its short-circuit at normal contacts 2 of the final selector being now open, and extends the loop. Called line busy. Relay T does not operate, the red lamp remains lit at the calling station, and no ring-back signal is heard. Called line free ; ringing. Relay T operates in series with relay IA which lights red lamp IR. Relay T operates relays D, ID, IID, E, of which relay D closes the filament circuit of triodes L1 ... L4, and connects the microphone circuits of the calling and called lines to transformers Tr1, Tr3, respectively ; relay ID connects the loud-speaker circuit of the calling line to transformer Tr4 and energizes relay IS to light the white lamp IBl at the called station ; whilst relay IID connects the loud-speaker circuit of the called line to transformer Tr2 and operates relay S to light the white lamp Bl at the calling station. Relay E connects buzzer Ro to transformer Tr1, its signals passing through amplifier L1 and transformer Tr2 to the calledparty's loud-speaker IHP. Some of the signal reacts upon the microphone IM and passes back through amplifier L3 and transformer Tr4 and thence partly to loud-speaker HP to give a ring-back signal and partly to rectifier L4 which after an interval operates relay IG. Relay IH operates due to the removal of a short-circuit and disconnects the calling relay E. Relay IC now operates, short-circuiting the called party's loud-speaker, disconnecting the anode circuit of amplifier L1, inserting a resistance IRS in the circuit of relay IS which drops its heavy (lower) armature and lights green lamp IV, and disconnecting relay S to light red lamp R. Contacts 6 of IC fleetingly shortcircuit relay IG to prevent it being influenced during these operations. Call refused. Operation of refusing key Idr releases relays T, IA and causes the re-operation of E and also the operation of relay NR which changes over the connections to triodes L1, L3 so that a buzzer signal passes to the calling subscriber who then releases the connection by operating key dr. Call accepted; talking circuits. When neither party is speaking, relays G, IG, H, IH, C, IC are de-energized and resistances RC, IRC are inserted to prevent singing. When subscriber St speaks, his microphone is connected over transformer Tr1, amplifier L1, transformer Tr2 to loud-speaker IHP. Some of the speech also passes to rectifier L2 to operate relay G which in turn operates H and C whereby resistance RC is cut out, the opposite path is shortcircuited, and the anode circuit of the opposite amplifier L3 is disconnected. Similar circuits exist for speech in the opposite direction. The sub-station lamps are also controlled by relays C, IC and indicate the condition of the circuits at any instant. Breaking-in ; stabilizing the circuits. Operation of key Iin by subscriber ISt when subscriber St is speaking operates relay IIN which disconnects relays G, H so that the interrupting subscriber may gain control of the system by speaking into his microphone. Keys in, Iin may also be used by the respective subscribers before each utterance, in the case of noise on the line which might hold relay G or IG operated. The circuits may be stabilized in one direction, i.e. rendered independent of the continuance of speech, by operating key ar which closes a circuit over wiper d of CA and winding W3 of Tr4 for the left-hand winding of relay F, already partially operated over its right-hand winding in parallel with C. Relay F now operates fully and holds relay H operated independently of G. It is still, however, possible for the other subscriber to break in by means of key Iin.