Grundig FG 5 Bedienungsanleitung Seite 11

A quartz oscillator generates a 312.5kHz square wave pulse, corresponding to
20 times the line frequency. Circuit stages, primarily equipped with ICs, form a
series of frequency dividers and generate line and frame pulses and all other
control pulses. :
A separate stage delivers line and frame blanking signals which are mixed with
the frame and line frequency signals. Finally, the mixed signal is combined with
signals containing individual picture information and then forms the composite
video signal.
The grey scale containing 8 steps is formed by adding square wave signals with
a repetition frequency with suitable multiple of the line frequency and with an
amplitude relationship derived from a suitable resistance matrix.
The cross-hatch pattern is generated by alternating a square wave signal of ten-
times line frequency with its complementary signal at several times the frame
frequency and by using this signal as video information.
The grid raster uses pulse spikes of 0.2 us duration for the vertical lines and of
64 us duration for the horizontal lines. The same stage also adds impules re-
quired for the circle display. Blanking signals allow individual displays of the
different line signals.
The circle video impulses are obtained from a comparator circuit, fed by the line
frequency and a parabolic shaped voltage which is again obtained from double
integration of the square wave line and frame blanking pulses.
The individual colour and colour synchronising potentials are derived from a
quartz oscillator which generates the colour sub-carrier of 4.433618 MHz at a
high degree of accuracy and constancy. To form the switched R-Y component,
corresponding to PAL requirements a 180° phase shift is applied to the colour
sub-carrier at alternating line frequency. Simultaneously there is a constant 90°
phase shift to generate the B-Y component. Both components pass through
identical amplifier stages with bi-filiar output circuits after which the vectors
-++ (R-Y) — (R-Y) + (B-Y) — (B-Y) reach the electronic switch.
This shapes in a resistance matrix the amplitude and phase of the alternating
burst and the individual colour signals. Depending on the control pulse applied,
a coloured area, the 4-vector display or the standard test picture will be formed.
A mixer stage superimposes the colour signal and burst upon the black-and-white
composite video signal. This stage also allows a 90° phase shift of the 4 colour
difference vectors with the burst angle remaining unchanged to generate the
special test pattern.
The composite video signal is fed to a phase reversal stage to obtain the correct
polarity required by the VHF and UHF modulators and to provide an inverse
signal for the video amplifier polarity switch. The 6 MHz sound carrier may be
added to the input of the phase reversal stage. If required, it may be modulated
with 1 kHz.
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