GB694091A - Improvements in multi-channel carrier telephone systems - Google Patents

Abstract

694,091. Carrier transmission. PUNCH ENGINEERING PTY., Ltd. Aug. 26, 1947 [Sept. 10, 1946], No. 23546/47. Class 40 (iv). In a single sideband multichannel carrier current telephone system transmitting a similar sideband in each of the contiguous channels, the filter economy obtained by a low signal bandwidth to carrier spacing ratio is increased by transmitting the carrier wave, so that the suppression of the lower signal frequencies in the unwanted sideband is not essential. Curves 7-9 and 16-18, Figs. 1 and 2, show the attenuation desirable to suppress unwanted energy from the adjacent band and the dotted curves show attenuation due to normal band. pass and low-pass filters in two channels in which the sidebands 1 and 3 obtained by modulating the carrier currents of frequency Sand R respectively are transmitted. Similar attenuation-frequency curves, Fig. 3, for a system using a lower signal bandwidth to carrier spacing ratio show that little filter economy is achieved since the unwanted sideband at the lowest signal frequency, i.e. point 31, must still be suppressed. The characteristic 34, Fig. 4, of the filter necessary in a system transmitting the carrier currents together with the signal sideband shows that considerably less attenuation is required in the region of point 31 and obviously appreciable filter economy is effected.