PAL SYSTEM TELEVISION MEASUREMENT : STEADY STATE (STATIC) SYNC GAIN DISTORTION

Steady State (Static) Sync Gain Distortion

DEFINITION
Steady state gain distortion of the sync signal is present when horizontal sync amplitude is dependent on APL. This parameter is evaluated by measuring sync amplitude at high and low APL (typically 12.5% and
87.5%). The amount of distortion may be expressed as a percentage of the amplitude at 50% APL or as a percentage of the maximum amplitude. This is an out-of-service test.
Steady-state gain distortion of the picture signal is also sometimes measured. In this case, the effects of APL changes on peak white are evaluated.
PICTURE EFFECTS
If only sync is affected, small amounts of static gain distortion will not be noticeable in the picture.
Large amounts of distortion may affect the ability of some equipment to derive synchronization information and/or to clamp the signal. If the picture signal is also affected, luminance levels will be APL dependent if
this type of distortion is present.
TEST SIGNAL
Any test signal with variable APL can be used to measure steady-state sync gain. A 700 mV signal element such as a white bar is required for steady-state picture gain measurements.

Figure 93. A staircase signal with variable APL.

MEASUREMENT METHODS
Waveform Monitor. 
To make a measurement, first select 50% APL and use the waveform monitor variable gain to set the sync
amplitude to 100%. Vary the APL of the signal to 12.5% and then to 87.5%. At each APL level, record the amplitude of sync. The peak-to-peak variation for the three levels, expressed in per-cent, is typically quoted as the steady-state sync gain distortion.
This measurement can be made with the 1781R voltage cursors in the RELATIVE mode.
Figures 94 and 95 illustrate the measurement procedure.

Figure 94. The sync pulse measures 300 mV at 50% APL.

Figure 95. At 87.5 APL, the sync pulse measures 260 mV. This indicates a steady-state distortion of about 13%.

Lihat juga

Table of Contents

Preface	3
Good Measurement Practices	4
EQUIPMENT REQUIREMENTS	4
CALIBRATION	6
INSTRUMENT CONFIGURATION	6
DEMODULATED RF SIGNALS	8
TERMINATION	8
DEFINITION OF THE PAL TELEVISION STANDARD	8
PERFORMANCE GOALS	8
Waveform Distortions and Measurement Methods	9
I VIDEO AMPLITUDE AND TIME MEASUREMENTS	9
Amplitude Measurements	10
Time Measurements	12
SCH Phase	15
II LINEAR DISTORTIONS	18
Chrominance-to-Luminance Gain and Delay	19
Short Time Distortion	24
Line Time Distortion	26
Field Time Distortion	28
Long Time Distortion	30
Frequency Response	31
Group Delay	36
K Factor Ratings	38
III NONLINEAR DISTORTIONS	41
Differential Phase	42
Differential Gain	46
Luminance Nonlinearity	50
Chrominance Nonlinear P h a s e	5 2
Chrominance Nonlinear Gain	5 3
Chrominance-to-Luminance Intermodulation	54
Transient Sync Gain Distortion	55
Steady-State (Static) Sync Gain Distortion	56
IV NOISE MEASUREMENTS	57
Signal-to-Noise Ratio	58
V TRANSMITTER MEASUREMENTS	6 0
ICPM	61
Depth of Modulation	63
GLOSSARY OF TELEVISION TERMS	64
APPENDICES
APPENDIX A - PAL COLOUR BARS	67
APPENDIX B - SINE-SQUARED PULSES