PAL SYSTEM TELEVISION MEASUREMENT : NOISE MEASUREMENT

IV. NOISE MEASUREMENTS

The electrical fluctuations that we refer to as noise form a very complex signal that does not lend itself to straightforward amplitude measurements. A number of special techniques have therefore been developed
for measuring noise. A comprehensive discussion of noise measurement is outside the scope of this publication. However, some of the methods which apply to television systems are discussed in this section.
Special filters are generally required for noise measurements.
These filters are used to separate the noise into its various frequency components for analysis. Each measurement standard typically calls for three or four measurements made with various combinations of the
filters. Note that specifications for the filters vary from standard to standard.
The tangential method of noise measurement, useful for making operational measurements of random noise, is the only method discussed in detail in this publication. While not the most accurate technique, the
tangential measurement can provide a quick way of keeping track of system noise performance over time. Tangential noise measurements are made with a specially equipped waveform monitor. This feature
is standard in the 1781R.
Specialized equipment is required to completely characterize the noise performance of a system. Until recently, these capabilities were available only in dedicated noise measurement instruments. The VM700T,
however, makes highly accurate noise measurements using filters implemented in software. The noise measurement features of the VM700T are reviewed briefly in this section.


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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