GB525628A - Improvements in or relating to television transmitting and receiving systems - Google Patents

Abstract

525,628. Television; duplex wireless signalling. KALLMANN, H. E. Feb. 24, 1939, No. 6123. [Classes 40 (iii) and 40 (v)] Vision and accompanying sound are transmitted by one carrier which is modulated in both frequency and amplitude. Sound signals after amplification at 5, 6, Fig. 1, are frequency modulated at 7 on to a carrier from 4. The resultant carrier passes through an amplitude limiter 8 and at 9 receives vision and synchronizing signals as an amplitude modulation, and is transmitted at 14. The signal is received at 21, Fig. 2, amplified at 22, and passed through a detector and amplifier 25 to the vision receiver 23. The presence of frequency modulation in this channel does not affect the picture. The sound channel passes through an amplifier 30 to an amplitude limiter 31 which removes the vision signal, and also the synchronizing signals if they are not constituted by a cessation of the carrier and thence to a frequency detector 32, which may be constituted by balanced diodes 33, 34, Fig. 3, associated with circuits 35, 36 tuned above and below the normal carrier frequency. The use of frequency modulation for the sound channel renders it less liable to interference from motor vehicle ignition systems. If synchronizing signals are constituted by cessation of carrier then a low-pass filter 37 will remove the short duration line pulses. However long duration frame pulses could not be removed, so frame pulses can be made of the same duration as line pulses, but transmitted out of phase with the line pulses, for example “ and ¥ of a line interval away from a line pulse in an interlaced scanning system. Two associated transmissions can be made on one carrier by using crossed polarized aerials. Specifications 489,094, 489,102, 504,766 and 505,079 are referred to.