GB1498127A - Video communication system through media of narrow bandwidth - Google Patents

Abstract

1498127 Television NISSAN MOTOR CO Ltd 16 May 1975 [25 May 1974] 20914/75 Heading H4F Bandwidth reduction in a video telephone system is achieved by dividing the 4 MHz bandwidth signal from camera 11, Fig. 1, into high and low frequency components. The signal is applied to a low pass filter 12 of pass band 0-1 MHz and to a band pass filter 13 of 2-3 MHz pass band. The components are modulated on to carriers by respective modulators 14, 16 supplied with 900 MHz and 898 MHz so that signals in the band 900 to 901 MHz are provided. A switch 18, driven at the line rate by sync. generator 19, selects alternately, a line of low frequency components and a line of high frequency components for transmission over a 1 MHz band pass channel 10. At the receiver sync. is extracted which drives a switch 22 to pass alternate lines to respective demodulators. Each demodulated high or low frequency component is stored in a respective one line delay and added to the subsequent low or high frequency component of the adjacent line in a mixer stage prior to display. This eliminates a striped effect produced by displaying adjacent lines of differing frequency range signal. A system for normally selecting a high pass band of either 2-3 MHz or 3-4 MHz, for the high frequency component, is described with reference to Figs. 2 and 3 (not shown).