GB624740A - Improvements relating to television transmitters and receivers or the like - Google Patents

Abstract

624,740. Diplex pulse signalling; pulse modulation. STILLWELL, P. F. T. C. Jan. 27, 1947, No. 2417. [Class 40 (v)] In a modulated pulse transmission system, audio signals are divided into a band below half the pulse repetition frequency, and a band above that frequency which is mixed with local oscillations to produce a second band of frequencies below half the pulse repetition frequency, both resulting bands being transmitted separately. As applied to a 605-line television system in which the synchronizing pulses are modulated by the audio signals, said signals are passed to both a 0-6 kc/s. filter 8, Fig. 2, and a 6-10 kc/s. filter 9. The output of filter 8 modulates the width of the synchronizing pulses. The output of filter 9 modulates the output of an 11 kc/s. oscillator 12, the resultant lower sideband being selected by the filter 13 and used to width modulate further pulses arranged to follow the synchronizing pulses during the blanking interval. Alternatively, the synchronizing pulses may be modulated both in width and amplitude to carry both parts of the audio signal. At the receiver, Fig. 3, the two sets of pulses are separated by gating, the synchronizing pulses are demodulated by a filter 14, whilst the further pulses are demodulated by a filter 16 before being mixed with 11 kc/s. oscillations from an oscillator 18, the lower sideband being passed by filter 19 and added to the other band of signals. For a low fidelity receiver only the 0-6 kc/s. band of signals need be demodulated. Specification 613,857 is referred to.