PAL SYSTEM TELEVISION MEASUREMENT : K FACTOR RATINGS

K Factor Ratings

DEFINITION
The K Factor rating system maps linear distortions of 2T pulses and line bars onto subjectively determined scales of picture quality. The various distortions are weighted in terms of impairment to the picture.
The usual K Factor measurements are Kpulse/bar, K2T, Kbar, and sometimes K50 Hz. The overall K Factor rating is the largest value obtained from all of these measurements. Special graticules can be used to obtain the K factor number or it can be calculated from the appropriate formula.
Definitions of the four K factor parameters are as follows:
K2T.
K2T is a weighted function of the amplitude and time of the distortions occurring before and after the 2T pulse. In practice, a graticule is almost always used to quantify this distortion.
Different countries and standards use slightly different amplitude weighting factors. An example is shown in Figure 55.
Kpulse/bar.
Calculation of this parameter requires measurement of the pulse and bar amplitudes.
Kpulse/bar is equal to: 1/4 [ (pulse-bar)/pulse ] X 100%.
It should be noted that some documents, including CCIR 567-2, recommend that the (bar-pulse) quantity be divided by the bar amplitude rather than the pulse amplitude. The two definitions will yield very nearly the same answer for practical levels of distortion. Check for the definition recommended by the appropriate broadcast authority.
There are also some definitions of Kpulse/bar that provide signed rather than absolute value results. Since there are several different definitions in use, it is again recommended that the definition be verified.
Kbar.
A line bar (10 or 25 microseconds) is used to measure Kbar.
Locate the centre of the bar time, normalize that point to 100%, and measure the maximum amplitude deviation for each half. Ignore the first and last 2.5% of the bar. The larger deviation of the two, expressed
in percent, is generally taken as the Kbar rating. The peak-to-peak deviation is sometimes quoted,
particularly if a 10 microsecond bar is used. This is another case where it is recommended the definition and test signal in use be verified and the information recorded along with the measurement result.
K50 Hz.
A field-rate square wave is used to measure this parameter.
Locate the centre of the field bar time, normalize that point to 100%, and measure the maximum
amplitude deviation for each half. Ignore the first and last 2.5%. The larger of the two tilt measurements, divided by two, is the K50 Hz rating.

Figure 55. The 1781R external graticule includes a 5% K2T limit.

PICTURE EFFECTS
All types of linear distortions affect K Factor rating. Picture effects may include any of the aberrations discussed in the sections on short time, line time, field time, and long time distortions.
Since overall K factor rating is the maximum value obtained in the four measurements, the picture effects cor responding to a given K Factor rating may vary widely.
TEST SIGNAL
Any test signal containing a 2T pulse and a white bar can be used to measure K2T, Kpulse/bar, and Kbar. A 50 Hz square wave is required for measurement of K50 Hz.

Figure 56. This signal contains the pulse and bar elements required for K Factor measurements.

MEASUREMENT METHODS
Waveform Monitor.
The external graticule provided with 1781R and 1481 waveform monitors includes special marks for making K Factor measurements.
To make a K2T measurement, use the vertical position control to set the black level to coincide with the 0.3 volt graticule mark.
Then use the variable gain control to set the top of the 2T pulse to the 1 volt graticule line (see Figure 57). Set the horizontal magnification to 0.20 microseconds per division. Under these conditions, the K2T graticule
indicates a 5% limit. Enabling the X5 vertical gain, in addition to the variable gain required to normalize the pulse height, will change the graticule indication to a 1% limit.
The 1781R is also equipped with an electronic K2 T graticule. Select K FACTOR in the MEASURE
menu and make sure that the horizontal magnification is set to 0.20 microseconds per division.
Set the black level of the signal to overlay the dotted electronic graticule line and adjust the pulse amplitude until it reaches the small cross drawn electronically near the top of the screen.
Use the large front panel knob to adjust the graticule size until it just touches the waveform at the point of greatest distortion. The readout will now indicate the K2T distortion in percent.

Figure 57. A 2T pulse properly positioned for a K2T measurement. This signal has a K2T distortion of slightly more than 5%.

Figure 58. The 1781R electronic K Factor graticule measures a 2.5% K2T distortion for this signal.



The external 1781R (and 1481) graticule includes Kpulse/bar marks in the centre near the top. To use
this graticule, normalize the pulse amplitude (or the bar amplitude, depending on the definition in use) to extend from 0.3 to 1.0 volts. Then compare the other signal element to the Kpulse/bar scale to obtain a
K Factor reading in percent.
There is also a 5% Kbar limit near the upper left-hand corner of the external graticule. This limit is designed for use with a 10 microsecond bar when a 1H sweep is selected. Position the waveform horizontally so that
the rising and falling edges of the bar pass through the graticule circles on the 0.65 volt line (see Figure 60). The waveform vertical gain should be adjusted so that the black level coincides with the 0.3 volt line and the
centre of the bar passes through the cross in the centre of the Kbar box.

Figure 59. With the pulse taken as the reference, the 1781R graticule indicates that this signal has a Kpulse/bar distortion of 2%.

Figure 60. This signal is properly positioned for a Kbar measurement with the 1781R graticule.


VM700T Automatic Measurement.
Select K FACTOR in the VM700T MEASURE mode to obtain a measurement of K2T.
The graticule can be set to automatically track the waveform or manually adjusted with the front panel knob. This display also provides numeric K2T and Kpulse/bar results (see Figure 61). Measurements of these parameters are also available in the VM700T AUTO mode. The VM700T provides a signed Kpulse/bar result that is negative when the pulse amplitude is smaller than the bar amplitude.

Figure 61. The VM700T 2T Pulse K Factor measurement.

NOTES
17. Pulse-to-Bar Definitions. 
There are several different methods of expressing the relationship between pulse amplitude and bar amplitude. It is important to understand the difference and know which method is specified.
Three of the most common definitions are given below.
PULSE-TO-BAR RATIO = (pulse/bar) X 100%
PULSE-BAR INEQUALITY = (pulse-bar) X 100%
K PULSE-TO-BAR = 1/4 [ (pulse-bar)/pulse ] X 100%


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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