PAL SYSTEM TELEVISION MEASUREMENT : GLOSSARY OF TELEVISION TERMS

GLOSSARY OF TELEVISION TERMS

AC-COUPLED 
A connection which removes the constant voltage (DC component) on which the signal (AC component) is riding. Implemented by passing the signal through a capacitor.
AM — Amplitude Modulation 
(AM) is the process by which the amplitude of a high-frequency carrier is varied in proportion to the signal of interest. In the PAL television system, AM is used to encode the colour information and to transmit the picture.
Several different forms of AM are differentiated by various methods of sideband filtering and carrier suppression. Double sideband suppressed carrier is used to encode the PAL colour information, while the signal is transmitted with a large-carrier vestigial sideband scheme.
APL — Average Picture Level.
The average signal level (with respect to blanking) during active picture time, expressed as a percentage of the difference between the blanking and reference white levels.
BACK PORCH
The portion of the video signal that lies between the trailing edge of the horizontal sync pulse and the start of the active picture time.Burst is located on back porch.
BANDWIDT
The range of frequencies over which signal amplitude remains constant (within some limit) as it is passed through a system.
BASEBAND 
Refers to the composite video signal as it exists before modulating the picture carrier. Composite video
distributed through a studio and used for re c o rding is at baseband.
BLACK BURST
Also called “colour black”, black burst is a composite video signal consisting of all horizontal and vertical
synchronization information and burst. Typically used as the house reference sychronisation signal in television facilities.
BLANKING LEVEL
Refers to the 0.3 volt level (with respect to sync tip) which exists before and after horizontal sync and during
the vertical interval.
BREEZEWAY 
The portion of the video signal that lies between the trailing edge of the horizontal sync pulse and the start of burst. Breezeway is part of back porch.
BROAD PULSES
Another name for the vertical synchronizing pulses in the center of the vertical inter-val. These pulses are
long enough to be distinguished from all others, and are the part of the signal actually detected by vertical sync separators.
BRUCH BLANKING
A 4-field burst blanking sequence employed in PAL signals to ensure that burst phase is the same at the
end of each vertical interval.
BURST
A small reference packet of the subcarrier sine wave sent during the horizontal blanking interval on every line
of video. Since the carrier is suppressed, this phase and frequency reference is required for synchronous demodulation of the colour difference signals in the receiver.
B-Y
One of the colour difference signals used in the PAL system, obtained by subtracting luminance (Y) from the blue camera signal (B).
CHROMINANCE 
Chrominance refers to the colour information in a television picture. Chrominance can be further
broken down into two properties of colour, hue and saturation.
CHROMINANCE SIGNAL 
The high-frequency portion of the video signal, obtained by quadrature amplitude modulation
of a 4.43 MHz subcarrier with R-Y and B-Y information.
COLOUR BLACK
See Black Burst.
COLOUR DIFFERENCE SIGNALS
Signals used by colour television systems to convey colour information in such a way that the signals go to zero when there is no colour in the picture. U and V are colour difference signals.
COMPONENT VIDEO
Video which exists in the form of three separate signals, all of which are required in order to completely specify the colour picture. For example: R, G and B or Y, R-Y and B-Y.
COMPOSITE VIDEO
A single video signal containing all of the necessary information to reproduce a colour picture.
Created by adding quadrature amplitude modulated U and V to the luminance signal.
CW — Continuous Wave.
Refers to a separate subcarrier sine wave used for synchronization of chrominance information.
dB (DECIBEL) — A decibel is a logarithmic unit used to describe signal ratios. For voltages,
dB = 20 Log10 (V1 /V2).
DC-COUPLED
A connection configured so that both the signal (AC component) and the constant voltage on which it is riding (DC component) are passed through.

DC RESTORER
A circuit used in picture monitors and waveform monitors to clamp one point of the waveform to a fixed DC level.
DEMODULATOR
In general, this term refers to any device which recovers the original signal after it has modulated a high frequency carrier. In television, it may refer to:
(1) An instrument, such as a Tektronix TV1350 or 1450, which takes video in its transmitted form (modulated onto the picture carrier) and converts it to baseband.
(2) The circuits that recover U and V from the composite signal.
EQUALIZING PULSE
The pulses that occur before and after the broad pulses in the
vertical interval.
ENVELOPE DETECTION
 A demodulation process in which the shape of the RF envelope is
sensed. This is the process used by a diode detector.
FIELD 
In interlaced scan systems, the information for one picture is divided up into two fields. Each field contains half of the lines required to produce the entire picture. Adjacent lines in the picture are in alternate fields.
FM — Frequency Modulation
(FM) is the process by which the frequency of a carrier signal is varied in proportion to the signal of interest. In the PAL television system, audio information is transmitted using FM.
FRAME
A frame (sometimes called a “picture”) contains all the information required for a complete picture. For interlaced scan systems, there are two fields in a frame.
FRONT PORCH
The portion of the video signal between the end of active picture time and the
leading edge of horizontal sync.
GAMMA 
Since picture monitors have a non-linear relationship between the input voltage and brightness, the signal must be correspondingly predistorted.
Gamma correction is always done at the source (camera) in television systems: the R, G and B signals are converted to R1/g, G1/g and B1/g. Values for gamma range from 2.2 to 2.8.
GENLOCK
 The process of locking both sync and burst of one signal to sync and burst of another, making the two signals completely synchronous.
HARMONIC DISTORTION — If a sine wave of a single frequency is put into a system, and harmonic content at multiples of that frequency appears at the output, there is harmonic distortion present in the system. Harmonic distortion is caused by non-linearities in the system.
HORIZONTAL BLANKING
Horizontal blanking is the entire time between the end of the active picture time of one line and the beginning of active picture time of the next line. It extends from the start of front porch to the end of back porch.
HORIZONTAL SYNC 
Horizontal sync is the 300 mV pulse occurring at the beginning of each line. This pulse tells the picture monitor to go back to the left side of the screen and trace another horizontal line of
picture information.
HUE
Hue is the property of colour that allows us to distinguish between colours such as red, yellow, purple, etc.
HUM 
Hum refers to the undesirable coupling of the 50 Hz  power sine wave into other
electrical circuits.
INTERCARRIER SOUND
A method used to recover audio information in the PAL system. Sound is separated from video by beating the sound carrier against the video carrier, producing a 5.5 MHz IF that
contains the sound information.
ITS — Insertion Test Signal.
A test signal which is inserted in one line of the vertical interval to facilitate in-service testing.
LINEAR DISTORTION 
Refers to distortions that are independent of signal amplitude.
LUMINANCE 
The signal which represents brightness, or the amount of light in the picture . This is the only signal required for black and white pictures, and for colour systems it is obtained as a weighted sum (Y = 0.3R + 0.59G + 0.11B) of the R, G and B signs.
MODULATED
When referring to television test signals, this term implies that chrominance information is present. (For example, a modulated ramp has sub-carrier on each step.)
MODULATION
 A process which allows information to be  moved around in the frequency domain in order to facilitate transmission or frequencydomain multiplexing. See AM and FM for details.

NON-LINEAR DISTORTION — Refers to distortions that are amplitude-dependent.
NTSC — National Television System Committee. The organization that developed the television
standard currently in use in the United States, Canada and Japan. Now generally used to refer to that standard.
PAL — Phase Alternate Line. 
Refers to one of the television systems used in Europe and many other parts of the world. The phase of one of the colour difference signals alternates from line to line to help cancel out phase errors.
QUADRATURE AM 
A p rocess which allows two signals to modulate a single carrier frequency. The two signals of interest Amplitude Modulate carrier signals which are the same frequency but differ in
phase by 90 degrees (hence the Quadrature notation). The two resultant signals can be added together, and both signals recovered at the other end, if they are also demodulated 90 degrees apart .
QUADRATURE DISTORTION
 Distortion resulting from the asymmetry of sidebands used in vestigial sideband television transmission. Quadrature distortion appears when envelope detection is used, but can be eliminated by using a synchronous demodulator.
RF — Radio Frequency. In television applications, RF generally refers to the television signal after the picture carrier modulation process.
RGB — Red, Green and Blue. 
The three primary colours used in colour television's additive colour reproduction system. These are the three colour components generated by the camera and used by the picture monitor to produce a picture.
R-Y 
One of the colour difference signals used in the PAL system, obtained by subtracting luminance (Y) from the red camera signal (R).
SATURATION 
The property of colour which relates to the proportion of white light in the colour. Highly saturated colours are vivid, while less saturated colours have more white mixed in and therefore appear pastel. For example, red is highly saturated, while pink is the same hue but much less saturated.
In signal terms, saturation is determined by the ratio between luminance level and chrominance amplitude. It should be noted that a vectorscope does not display saturation: the length of the vectors represents chrominance amplitude. In order to verify that the saturation of the colours in a colour bar signal is correct, you must check luminance amplitudes with a waveform monitor in addition to observing the vectors.
SUBCARRIER
 Refers to the high-frequency signal used for quadrature amplitude modulation of the colour difference signals. For PAL, subcarrier frequency is 4,433,618.75 Hz.
SYNCHRONOUS DETECTION —  A demodulation process in which the original signal is recovered by multiplying the modulated signal with the output of a synchronous oscillator locked to the carrier.
TERMINATION 
In order to accurately send a signal through a transmission line, there must be an impedance at the end which matches the impedance of the source and of the line itself. Amplitude errors and reflections will otherwise result. Video is a 75 Ohm system, so a 75 Ohm terminator must be put at the
end of the signal path. U — The B-Y signal after a weighting factor of 0.493 has been applied. The weighting is necessary to reduce peak modulation in the composite signal.
UNMODULATED
When re f e rring to television test signals, this term refers to pulses and pedestals which do not have high-frequency chrominance in-formation added to them.
V — The R-Y signal after a weighting factor of 0.877 has been applied. The weighting is necessary to reduce peak modulation in the composite signal.
VECTORSCOPE 
A specialized oscilloscope which demodulates the video signal and presents a
display of V versus U. The angle and magnitude of the displayed vectors are respectively related to hue and saturation.
VERTICAL INTERVAL
 The synchronizing information that appears between fields and tells the picture monitor to go back to the top of the screen to begin another vertical scan. Y — A b b reviation for luminance.
ZERO CARRIER REFERENCE
 A pulse in the vertical interval which is produced by the demodulator to provide a reference for evaluating depth of modulation.


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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