Patent GB-259328-A (GB)
Title: Improvements in wave signalling systems
IPC: H04B1/66
Filed: 1925-07-21
Abstract: 259,328. Western Electric Co., Ltd., (Bell Telephone Laboratories, Inc.). July 21, 1925. Telephone currents, inverting and transposing frequencies of.-The original signal frequencies are changed prior to transmission, by being passed through a confined medium in which a rotary receiver moves with or against the signal wave-front at a speed comparable with the wave velocity through the medium, thereby modifying the output in accordance with Doppler's prin. ciple. The process is reversed at the receiving end to restore the signals to their original form. The wave is operated on in small portions, each portion being compressed to 1/n<th> its original duration. In order to fill up the gaps each small portion is repeated n times. Alternatively different signals may be transmitted simultaneously in one channel of a width n times the normal width allotted to each signal, in which case the elements are not repeated but the gaps are filled with one compressed portion of each of the separate signals. Thus the bands necessary to separate different signalling channels are eliminated. Or the signalling wave may be compressed uniformly throughout thereby increasing the available frequency channels in the transmitting medium, particularly in multiplex signalling. The concentration of signal energy allows of greater selectivity in reception and ensures a higher value of signal strength to interference noise. As an additional feature, for secret signalling, the coupling arrangement may be such as to introduce a reversal of wave amplitude with respect to time, the original form being restored at the receiving end. Fig. 1 is a diagram of the basic arrangement. The original signal wave flows through a channel A, B which may be either an artificial electric line or an air tube. A coupling or receiving element C moves with or against the wave front, and transfers the energy modified in accordance with Doppler's principle into the transmission line L. For a particular ratio between the speed of wave propagation and that of the arm C, the original signal-wave, represented by successive portions A - - G, Fig. 2, row (1) is sent to line L in the form shown in row (2). Each portion is compressed and repeated four times, the order of appearance being shown by the index numerals. At the receiving end R the compressed portions of the wave are picked up by the " expanding " arms 1, 2, 3, 4 of a similar coupling device C<1> in the order shown in row (3). Each arm therefore receives a wave similar in form to the original signal but out of phase as indicated in rows (4) to (7). Retardation lines L2 - - L4 are therefore inserted as shown in Fig. 1, between the respective arms and the final receiving device, and effect the readjustment indicated in rows (8) - - (11), Fig. 2, where each element is synchronized and may be superposed to re-form the original wave. If the coupler arm C is rotated in the same direction as the signal wave the transformation may consist of a time reversal only. Or the wave front may be expanded in. stead of being compressed. Fig. 15 shows a practical embodiment of the coupling arrangement of Fig. 1. The signal wave from an artificial line A is fed into metal segments a on a stationary wheel b shunted across successive cells C, L of the line network. A second wheel c is mounted coaxially with the wheel b, and is rotated relatively thereto, carrying insulated plates d through which the modified currents are transferred to the output line B by electrostatic coupling. Or a similar coupling-device depending upon electromagnetic coupling may be employed. As shown in Fig. 19, the artificial line may be segmented into six parts, each terminated by a non-reflecting impedance network N. This reduces the degree of distortion inherent in the longer line one complete cycle of operation corresponding to the traverse of the rotating coupler over each single segment. Fig. 13 shows an arrangement for acoustic conversion. Two microphones 14, 15 mounted on radial arms are rotated in a circular air-tube 10 fed with air waves from a source of sound 12, the waves being led off through a pipe 13. The converted wave energy, in electrical form, is fed through slip-rings and brushes to an amplifier A &c.