GB1065026A - Improvements in or relating to colour television systems and colour television receivers for use therein - Google Patents

Abstract

1,065,026. Colour televisions. TELEFUNKEN PATENTVERWERTUNGSG.m.b.H. April 8, 1964 [April 10, 1963], No. 14590/64. Heading H4F N.T.S.C.-type signals are modified according to the P.A.L. method of transmission, whereby the phase of the I component of the colour sub-carrier is reversed for alternate lines, and in order to permit a switch at a receiver which restores the signal phase to be set in operation in the correct phase there is transmitted during the vertical flyback interval a series of special reference signals 4, Fig. 2, in addition to the normal colour synchronizing " bursts " 3 which follow the line synchronizing pulses 2. The reference signals are located on a direct voltage of approximately one half the maximum allowable sub-carrier amplitude, in order that they may be of substantial amplitude, and comprise oscillations of sub-carrier frequency which assume the phase of +Q and - Q in alternate lines. The phase of the normal synchronizing "bursts" remains fixed at +I. In a receiver the I and Q sub-carrier components are separated as illustrated in Fig. 3 by means of a delay demodulator 6, 7, 8, 9 and the additional reference signals produce outputs in the two channels as shown in Fig. 4. A single amplitude output A appears at the beginning and end of the series on each channel whilst intermediate outputs are of double amplitude in the I channel and zero in the Q channel. The I channel signal is used for controlling the switch operation and is selected by a synchronous demodulator operating at the +Q phase. Fig. 9 illustrates a receiver. The separated Q and I sub-carrier signals, which are in suppressed carrier form, are amplitude demodulated in stages 14 and 19, the required carrier being regenerated by an oscillator 12 (synchronized by the normal " bursts " at I phase) which is connected through a 90 degrees phase shifter 13 to stage 14 and through a phase reversing switch 18 to stage 19. Switch 18 is operated at line frequency by pulses 21. In accordance with the invention the switch is established in operation in the correct phase by the additional reference signals which are separated from the output of the I channel by a synchronous demodulator 24 supplied with a signal from oscillator 12 at the +Q phase over connection 26. To eliminate disturbance, by undesired signal components the connection before or after demodulator 24 may include a gate stage which is opened only during the vertical flyback interval, and the output of the demodulator may be applied to switch 18 via an amplitude discriminator. A more detailed circuit of a receiver is described with reference to Fig. 10 (not shown).