Patent GB-164242-A (GB)
Title: Improvements in high frequency electrical signalling systems
IPC: H04J1/10
Filed: 1920-06-15
Abstract: 164,242. Western Electric Co., Ltd., (Western Electric Co., Inc.). June 15, 1920. Wired wireless systems. - Modulated highfrequency carrier currents are transmitted over telephone or other low-frequency circuits, filters being used to exclude the high-frequency currents from the low-frequency terminal circuit and the low-frequency currents from the high-frequency terminal circuit. By a similar use of high and low frequency filters, the high-frequency currents may be conducted round a low-frequency repeater, or may be passed on from one to another of several distinct low-frequency circuits. For example, portions of two low-frequency circuits may be joined up in a single high-frequency circuit, to the exclusion of other portions which, owing to their being loaded or constructed in cable form, are unsuitable for high frequencies. In the multiplex carrier system shown in Fig. 1, the transmission circuit ML is connected through a low frequency filter LF to a terminal telephone line LT composited for morse signalling, and through a high-frequency filter HF to the carrier transmitting and receiving circuits TL, RL. The filter LF may consist of a number of series inductances and shunt capacities, to suppress currents of frequencies higher than the telephonic range, and the filter HF may consist of a number of series capacities and shunt inductances, to suppress currents of frequencies below the upper limit of the telephonic range. The carrier transmitting and receiving circuits TL, RL are associated with the line ML and with a balancing circuit N by means of a transformer 10 in such a way as to be conjugate with respect to each other. The balancing circuit N includes elements corresponding to the line ML and filters HF, LF, and may also include elements corresponding to the terminal telephone line LT and its compositing apparatus. In a similar way, branches TL1 - - TL4 and RL, - - RL4 of the circuits TL, RL are conjugately associated with telephone lines L, - - L, and balancing circuits M1 - - M4 and homodyne demodulators D, - - D4 N1 - - N4 by transformers 11 - - 14. Modulators in these branch circuits are supplied with carrier currents of different frequencies (for example 10,000, 15,000, 20,000, and 25,000) by an oscillation generator FG (producing oscillations of frequency 5,000) and a harmonic producer HP, filters CF1 - - CF4 and amplifiers CA1 - - CA4 being inserted in the branch connections. Outgoing modulated carrier currents are transmitted to the common circuit TL through filters such as TF1 and amplifiers such as TA1, the filters being designed to transmit currents of the corresponding carrier frequencies and of the neighbouring frequencies due to modulation. Incoming modulated carrier currents are sorted out by corresponding filters RF1 - - RF4, and after demodulation are delivered to the lines L, - - L4 through low-frequency amplifiers such as RA1 and filters such as RF1<1>, which suppress high-frequency currents. In addition to the harmonic carrier currents, currents of the fundamental frequency 5,000 are delivered to line through filters FF, FF' and amplifier FA, and are taken out at the distant station through a filter FR, so that a separate oscillation generator need not be provided at the distant station. The amplifiers, modulators, demodulators, oscillation generator and harmonic producer may be of the vacuum type.