MEASUREMENTS

K Factor Ratings
• 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 corresponding 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, K pu | se /b ar , and Kb ar . A 50 Hz square
wave is required for measurement of K50 Hz-
Figure 57. This signal contains the pulse and bar
signal 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, as shown in Figure 58. Set the
horizontal magnification to 0.20 microseconds per division.
Under these conditions, the K2T graticule indicates a 5% limit.
If you enable the X5 vertical gain in addition to the variable
gain required to normalise the pulse height, the graticule
indicates a 1% limit.
Figure 58. A 2T pulse properly positioned for a K.2J
measurement. This signal has a K?\ distortion of
slightly more than 5%.
The 1781R is also equipped with an electronic K2T 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 59. The 1781R electronic K Factor graticule
measures a 2.5% K?r distortion for this signal.
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