GB493026A - Improvements in or relating to radio communication systems - Google Patents

Abstract

493,026. Wireless signalling. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. April 4, 1938, No. 10321. Convention date, April 3, 1937. [Class 40 (v)] Signals are transmitted by means of at least two carrier frequencies, e.g. 1<1>, 2<1>, Fig. 1, and at least one modulation side band 31, none of the side bands lying between any two of the carrier waves, while at the receiver any or all of the side bands may be combined with any or all of the carriers. A receiver for the signals of Fig. 1 comprises a frequency changer 13, 14, I.F. amplifier and A.V.C. device 15, 17 and detector 16. When no fading occurs the output of the latter comprises two L.F. bands spaced apart by the frequency difference between the carriers 1<1>, 2<1>. The lower of the two is selected by filter 18 and fed to the reproducer 25. The upper is selected by filter 19 heterodyned at 20 by an oscillator 21 of frequency equal to the difference in carrier frequencies and also fed to the reproducer 25. When fading occurs one of the carriers may be missing, but only one of the L.F. channels is thus disabled. The channel 19, 20, 21 may be fed from a separate spaced receiving aerial to provide diversity reception and the carriers may be wobbled. The frequency of the local oscillator 21 may be automatically controlled by incoming signals and homodyne circuits may be associated with the detector 16.