Analog Television - Digital Video and Audio Broadcasting Technology - page 26

voltage reference in the terminals and is of special importance for this rea-
son. The sync amplitude is nominally 300 mV below black. The 50% va-
lue of the falling edge of the sync pulse is considered to be the timing refe-
rence in the analog video signal. The burst (s. Fig. 2.17.) is used as voltage
and phase reference for the color subcarrier. Its amplitude is 300 mV PP . In
practice, amplitude distortions of the burst have little influence on the pic-
ture quality.
Linear distortion leads to tilt on the white bar (Fig. 2.18.). This is also an
important test parameter. To measure it, the white bar is sampled at the be-
ginning and at the end and the difference is calculated which is then related
to the white pulse amplitude.
The 2T pulse reacts sensitively to linear distortion in the entire transmis-
sion channel of relevance. Fig. 2.19. shows the undistorted 2T pulse on the
left. It has been used as test signal for identifying linear distortion since the
seventies. A 2T pulse altered by linear distortion is also shown on the right
in Fig. 2.19. If the distortion of the 2T pulse is symmetric, it is caused by
amplitude response errors. If the 2T pulse appears to be unsymmetric, then
group delay errors are involved (non-linear phase response).

13s

A

B

21s

(BA)
Tilt = * 100%
bar amplitude

H sync (50% falling edge)

Fig. 2.18. Tilt on the white bar

The 20T pulse (Fig. 2.20., center) was created especially for measure-
ments in the color channel. It reacts immediately to differences between
luminance and chrominance. Special attention must be paid to the bottom
of the 20T pulse. It should be straight, without any type of indentation. In