Patent GB-146562-A (GB)
Title: Improvements in wireless and other signalling systems using high-frequency currents
IPC: H04J1/00
Filed: 1919-03-11
Abstract: 146,562. Western Electric Co., (Western Electric Co.). March 11, 1919. Electric oscillations in line wires, telephoning and signalling by; wireless telegraphy and telephony; electric oscillations, producing.-Relates to duplex and multiplex working for wireless or wire transmission systems using high-frequency currents. In order that the transmitted currents may not affect the local receiving circuits, a differential arrangement is used in which the impedance of the transmission line or antenna is balanced by an ohmic resistance of a value equal to #L/C per unit length of line, where L and C denote the distributed inductance and distributed capacity of the line. In multiplex working in which currents of several frequencies are impressed on the line from separate generators, antiresonant or rejector circuits are connected in shunt to each individual transmitter circuit, thereby offering a path of high impedance to currents supplied by the associated transmitter, but offering a low impedance path to currents of other frequencies from the other transmitters. When messages are sent in both directions over the line by currents of different frequencies, the frequencies of the currents transmitted from one station are chosen intermediate those transmitted from the other, thereby increasing the number of signal channels in an available frequency range. The invention is shown applied to a wire-wireless telephone system in which the line L is connected at one station to three transmitter circuits T1, T2, T3 and to three receiving-circuits R1, R2, R3 or alternatively to the three circuits R<1>1, R<1>2, R<1>3. In the valve generator 0, the resonant circuit 10 12 is connected across the grid and plate of the valve 13, the filament being connected at the point 18 to the inductance 10. The oscillations from the valve 13 are modulated by the voice curnents from the microphone t in the modulator valve 1, the output circuit of which is connected to a rejector circuit 33, 34 tuned to the frequency of the generator 13. The modulated waves, amplified by the valves 2, 3, are supplied through the transformer 4 to the transmission line L. Similarly, modulated waves of other frequencies are supplied from the other transmitting-circuits T2, T3 through transformers 5, 6. In order that the energy from each transmitter may pass to line without encountering the impedance of, or being shunted by, the other transmitting-circuits, and also in order to remove the impedance of all the transmitters from the line so far as the incoming energy is concerned, rejector circuits C1, C2, C3 are connected in shunt to the secondary of each transformer 4, 5, 6, each rejector circuit 54, 55, say, being tuned to the approximate frequency of its associated transmitter, thus offering a path of high impedance to currents from the associated transmitter, but of low impedance to currents from the other transmitters and to currents incoming from other stations. To prevent the transmitted currents affecting the local receiving- circuits, the circuit 62, 63 is connected to line at the middle point 64 of the primary of a transformer, the secondary of which is connected to the receiving-circuits. The impedance of the line is balanced by an artificial line 65, which consists of an ohmic resistance; it is shown mathematically in the Specification that a line with uniformly distributed inductance and capacity tends to act as a pure resistance at high frequencies. The received waves may be separated with the aid of filters 71, 72, 73 before amplifying, as shown at R<1>1, R<1>2, R<1>3 or, preferably, the received waves are amplified by a valve 76 and then selected by tuned circuits, such as 83, 86, and detected by the valve 87 and telephone R1. Wave frequencies from 5000 to 50,000 are suitable for use in the system described, but at these relatively low frequencies the distortion of speech by the tuned selective circuits may be considerable. To remedy this, the tuned circuits may be replaced by a system of circuits which will selectively transmit the required band of frequencies with approximately the same attenuation for each frequency, for example, a filter having a relatively flat-topped transmission characteristic.