GB1125354A - Improvements in or relating to colour television test signal generators - Google Patents

Abstract

1,125,354. Colour television. GRUNDIG E.M.V. ELEKTRO-MECHANISCHE VERSUCHSANSTALT, INH. MAX GRUNDIG. 27 April, 1967 [27 April, 1966], No. 19532/67. Heading H4F. The specification describes means for producing a test signal for a PAL colour television receiver, comprising a grid pattern signal and a colour bar pattern signal. Production of grid pattern signal:-A square wave crystal oscillator produces pulses at twice line frequency (it being assumed that a 625 line, 50 frames/sec picture is involved). A 1 to 625 divider 2 produces frame sync pulses (two per picture for interlacing purposes) at the output of signal shaper 4, and these cause circuit 5 to produce a horizontal bar pattern signal. The output of oscillator 1 is also fed to 1 to 2 divider 3, to produce pulses 1, Fig. 2, which in turn produce line sync pulses from shaper 6, and a vertical bar pattern signal from circuit 7. The two bar pattern signals are combined at 9 together with the combined sync signals from mixer 8. The output of circuit 9 constitutes the grid pattern signal. Production of colour bar pattern signal:-Pulses 1, at line frequency cause a bistable circuit 10 to feed switching pulses II, III to oscillators 11 and 12 respectively. Oscillator 11 works at a frequency slightly higher than the colour sub-carrier frequency and is started by the switching pulses II to give the synchronous burst IV during odd lines. Similarly oscillator 12 operating at a slightly lower frequency than the sub-carrier frequency produces the synchronous bursts V during even lines. The series of bursts are combined in mixer 13 and each line is broken up into six "bars" by means of the bar pattern output of circuit 7. In the section diagram of Fig. 3, the sub-carrier vector is stationary, such that the vector of the bursts IV rotate clockwise, and that of the bursts V rotates anticlockwise. Such opposite rotation on successive lines gives a coherent colour bar display after PAL switching in the receiver. At times t 0 at the beginning of a line-sync pulse the sub-carrier oscillation is in phase with whichever burst is present. 7Ás later at the start of the colour burst gate, on an odd line the vector of burst IV has a relative phase of +45‹ whilst at the same instance on an even line the vector of burst V has a relative phase of -45 degrees. The bursts thus have the required 90 degree relationship at the start of successive colour burst gates. Either the grid pattern signal, or the colour for pattern signal may be selected by switch 15.