Patent GB-251683-A (GB)
Title: Improvements relating to carrier wave systems
IPC: H04M7/16
Filed: 1925-02-02
Abstract: 251,683. Le Tall, F. W., (Westinghouse Electric & Manufacturing Co.). Feb. 2, 1925. Calling systems; thermionic modulating systems; duplex signalling; tuning-apparatus, control of; thermionic valve circuits. -In a wireless or wired wireless telephone system analogous to a lock-out party line system, of the kind in which any desired station is called by sending out an appropriate number of impulses composed of modulated oscillations, the transmitter contains a valve 9 which can function either as an audio-frequency generator for calling or as an amplifier for speaking. General description. The group of stations comprises a dispatcher's station which sends on a wave-length A1 and receives on a wave-length #2, and a number of substations which send to the dispatcher's station on the wavelength #2 and receive from it on the wave-length #1. When, however, one substation calls another it reverses the tuning of its own aerials so as to send on #1 and receive #2 similarly to the dispatcher's station. Fig. 1 shows chiefly the sending apparatus and Fig. 2 chiefly the receiving apparatus, the broken conductors 34, 35, 83, 78, 97, 79, 37, 40, of each figure being supposed continuous with those of the other. Normally the apparatus is ready to receive calls from the dispatcher's station on a wave-length #1 which is picked up by the aerial 21, Fig. 2, rectified as to high frequency by the valve 23, amplified by the lowfrequency amplifier 25, rectified by the lowfrequency rectifier 28, and applied to the relay 32 so that the selector arm 87, Fig. 1. is stepped round by the requisite number of impulses until by resting on the contact 86 it causes the call bell 96 to ring. When the receiver 36, Fig. 1, is lifted, the hook switch effects a rearrangement of circuits so that received voice currents, amplified by the valve 25, Fig. 2, are diverted through the transformer 33 to the receiver 36 : and outgoing voice currents from the microphone 16, Fig. 1, are applied through the valve 9, acting as amplifier, to the modulator 4 which modulates the oscillator 3. When one substation wishes to call another, it first changes over the tuning of its receiving and transmitting circuits, so that the transmitter aerial 1 acquires a wave-length #1 and the receiver aerial 21 a wave-length #2. This may be effected by means of the local selector arm 68 which can be stepped round through the stops by manipulating the dial switch 63. The effect of this is to cut out part of the transmitter aerial tuning inductance 2, and to increase the capacity in the receiver circuits at 46, 48, 51. The call is then sent out by manipulating the dial 63 so as to energize the relay 11 a given number of times. Each time the relay 11 is energized the valve 9 is converted into a low-frequency oscillator, and acts through the modulator 4 so as to modulate the otherwise continuous oscillation of the oscillator 3, as indicated in Fig. 4. Transmitting set. Voltage for the transmitter valves is supplied by the alternator 5 which is cut in by the relay 58 when this is energized through the relay 53 on the hook switch 36<a> being lifted. Filament current is supplied through the transformer 6, and plate voltage through the transformer 7<a> and rectifier 7. The connection between the oscillator 3 and modulator 4 is of the Heising or constant current type, and low frequency oscillations are supplied to the modulator 4 by the valve 9. When the relay 11 is not energized, these low frequency oscillations are the voice currents of the microphone 16 transformed at 12 and applied to the grid of the valve 9. When the relay 11 is energized, however, through the dial switch 63, the grid is cut off from the microphone transformer 12 and connected to the low frequency tuned reaction circuit 14 so that the valve 9 becomes a generator of low frequency oscillations. These are passed on to the modulator 4 for the purpose of emitting one of the modulating-impulses that make up a call. The grid and plate of the oscillator 3 are tapped off the aerial tuning inductance 2. For sending to the dispatcher's station the tuning inductance is arranged .as shown, but when another substation is to be called up part of the inductance must be shortcircuited through the armature 43 of a self-holding relay 44. This relay is energized from the source 5 (provided that this has been cut in by the raising of the switchhook) through the action of the relay 73, whose circuit is closed by the selector 68 or otherwise. the selector 68 being responsive to a train of ten impulses given by the dial switch 63. The selfholding circuit of the relay 44 is broken at 44<a> and the parts are restored to the position shown when the source 5 is cut out by the replacing of the receiver. Preventing interference between transmitting and receiving aerials. The aerials are operated by a tuned circuit which comprises the conductors 37, 40, Figs. 1 and 2, part of the inductance 2, Fig. 1, a condenser 41, Fig. 2, and resistance 39. When the wave-lengths are changed by the operation of the relay 44, the condenser 51 is added in parallel to the condenser 41. Receiving set. When the wavelength of the transmitter is changed as described above, the converse charge in the receiver circuits is effected through the armature 75 of the relay 44, which closes a circuit including the conductor 78, battery 76, earth return 79, and relays 45, 47, 49, in parallel. The relays 45, 47, when energized, add capacity to the aerial and tuned secondary circuits respectively, while the relay 49 adjusts the separator circuit as described above. Received signals are rectified at 23 and the low frequency output is amplified by the valve 25. When the receiver 36, Fig. 1, is off the hook, the relay 26 is energized through the conductor 97, and in that case the output of the valve 25 is taken through the transformer 33 and conductors 34. 35, to the receiver 36. Receiving calls : selector circuits. When on the other hand the receiver 36, Fig. 1, is on its hook the relay 26, Fig. 2, is de-energized, and the output of the valve 25 is passed through the transformer 27 to the low-frequency rectifier 28. The call signal comprises the unbroken carrier wave modulated at intervals so as to produce a given number of modulation impulses, too such impulses being shown in part at p, and q, Fig. 4. The grid of the low frequency rectifier 28 acquires a blocking charge on the receipt of each of these impulses and so causes the relay 32 to release its armature 32<a> and close the circuit of the relay 84, Fig. 1. The selector arm 87 is thus stepped round, and if the number of impulses is that appropriate to the station the circuit of the bell 96 is closed by the relay 89 on the energization of this through the contacts 86, 87, conductors 88, 92, and battery 59. The selector arm 87 after a short pause returns to its normal position in the usual way, but the circuit of the relay 89 is held on by the relay 91, and the bell continues to ring until the switchhook is lifted, when the relay 17 is energized and the hold-on circuit is broken at 17<a>. A station cannot be called when its switch hook is lifted, the calling action being interrupted by the relay 17 and also by the relay 26. Sending calls. As described above, carrier radiation is continuously emitted so long as the switch-hook is lifted, and a call is effected by modulating the radiation, at intervals, a given number of times. For this purpose the dial switch 63 is manipulated so as to energize the relay 11 the required number of times. When the relay 11 is energized the grid of the valve 9 is connected to the filament through a tuned reaction coupling 14. The valve thus becomes a low frequency oscillator which acts through the modulator 4 on the oscillator 3.