GB197758A - Improvements in carrier wave transmission systems - Google Patents

Abstract

197.758. Western Electric Co., Ltd., (Western Electric Co., Inc.). Feb. 27, 1922. Wired wireless systems.- In a carrier-wave system, the transmission efficiency is automatically kept constant in spite of varying conditions of leakage. Telephone. current from line 7, Fig. 1, and a carrier current from a harmonic generator 11 at station A are supplied to a modulator 10 which sends modulated current to the line 1 through the balanced transformer 20. At the same time the fundamental frequency of the harmonic producer 11 is sent out through the filter 22, amplifier 23, and filter 24. At the station B, Fig. 2, the fundamental frequency is separated by a filter 26 and fed tc a harmonic producer 27 which supplies demodulatory currents to the device 31 which is also fed with the modulated current through the filter 30. The output current of the demodulator 31 is fed to the line 36. Fig. 3 shows the relation between, the unmodulated currents supplied to modulators and demodulators and their output current. The amplifier 23 at station A is so arranged that the amplitude of the fundamental frequency is such that under normal conditions the unmodulated current derived from it has an amplitude OD, which is greater than that required to produce a maximum output current from the demodulator 31. If, owing to line conditions, the fundamental becomes attenuated so that its amplitude is (say) OC, the output of the demodulator tends to rise to the value CG but owing to the attenuation suffered also by the modulated wave the actual output is CF which is equal to DE. In transmitting from station B, if the, fundamental has become attenuated, the output of the modulator 38 is increased to CG which is a value such that owing to attenuation the output of demodulator 16 at station A will be CF. Only one channel is shown but a number of messages are sent simultaneously over the line 1 by a modulator and demodulator at each station associated with each harmonic generated by the device. 11. In the application of the invention to a system wherein an unmodulated wave is sent along with one or both side bands, the amplitude of each unmodulated wave is controlled instead of that of a fundamental wave. The line 1 is also used for low frequency telegraphy coming in from line 2 including the usual composite set 3.