Fluke PM5414V - Handbuch (Seite 26)

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3 - 1 2 OPERATING INSTRUCTIONS PM 5414 V
Multiburst contains eight full screen vertical bars of definition lines in the frequency ranges 0.8,
1.8, 2.8, 3.0, 3.2, 3.4, 3.8, and 4.8 MHz. This checks the bandwidth of the video or iuminance
amplifier in black and white or color TVs as well as the resolution of monitors and video
recorders.
9. VCR is a specially designed test pattern to check the bandwidth, linearity, sensitivity, and AGC
of the chroma amplifiers in color video recorders. This combined test pattern is divided into the
following four horizontal segments:
- Horizontal 100 % white bar covering 1/6 field for exact level adjustment.
- Eight bars of resolution of which 2.8 - 3.0 - 3.2 - 3.4 MHz are used to align the high-pass filter
for a maximum resolution in VCR bandwidth.
- The next part of the pattern contains eight steps of decreasing iinear leveis of saturation from
100 % to 0 % to check the chroma amplifier linearity and color AGC circuitry. For example,
if the chroma writing current is too high, color will be visible in the last bar where no color
should be seen normally.
- The bottom section consists of a black horizontal bar with a moving white field to check video
recorders on moving pictures.
10. Color bar: a standard color bar pattern. The vertical bars are white, yellow, cyan, green,
magenta, red, blue and black. The luminance content depends on the TV system selected and
is automatically correct after the user makes the selection. The color bar pattern in fact provides
sufficient information for a good overall check on color performance. This includes the checks
on burst keying, subcarrier regeneration, RGB amplifiers, the delay color versus B/W signal and
saturation check.
If the color bar is combined with the white pattern, the white pattern appears in the lower third
part of the screen as reference to adjust the amplitude of the color difference signals with respect
to the luminance signal on the picture tube. This signal can be used for realigning the signal
amplitude of the demodulators and matrix circuitry, as the output can be compared with the
reference bar. For example, the blue and green guns can be switched off to allow the amplitude
of the R-Y signal to be adjusted. This is done by ensuring that no difference in brightness is
observed between bars five and six and the horizontal reference bar. In a similar fashion, the
amplitude of the B-Y demodulator can be determined. After this test, the matrix circuit can be
checked with only the green gun switched on.