GB1481305A - Information transmitting and receiving systems - Google Patents

Abstract

1481305 Quadraphonic systems EMI Ltd 13 Sept 1974 [13 Sept 1973 7 June 1974] 42982/73 and 25360/74 Heading H4R In a broadcast transmitter a matrix encoder receives four input signals, operates on the input signals to provide a corresponding number of composite signals, each including components derived from at least three of the input signals, and a carrier wave is modulated with selected combinations of the composite signals, and a pilot tone, to provide a broadcast signal the frequency bandwidth of which is substantially the same as that employed for conventional stereophonic broadcasts. As described the matrix encoder, Fig. 1 (not shown), is fed with R F , R B , L F , and L B , signals of a quadraphonic system to provide composite signals of the form The composite signals are transmitted according to one of the systems shown in Figs. 4a, 4b, of 4c. In each case the base-band signal is formed by the signal S L + S R , and the lower sideband of a 38 kHz subcarrier carries the signal S L - S R , to make the transmission compatible with a monophonic or stereophonic transmission. The upper sideband of the 38 kHz carrier carries a signal which is band limited to 3 kHz and comprises S LO , S LO - S RO or S L - S R while a further subcarrier at a frequency of 57 kHz, i.e. <SP>3</SP>/ 2 Î the 38 kHz subcarrier, carries a signal which is band limited to 3 kHz and comprises S RO , on the lower sideband only, a double sideband signal S LO + S RO , or the lower sideband carries S LO + S RO and the upper sideband S LO - S RO At the receiver Fig. 2 (not shown) the received signal is demodulated and the signals S L , S R , S LO , S RO , recovered and fed to a matrix to recover the signals L<SP>1</SP> F , L<SP>1</SP> B , R<SP>1</SP> F , R<SP>1</SP> B , which differ from the original signals only in the reduction of some high frequency components.