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Performance Verification: Analog Section
4-12
WFM90D and WFM91D Service Manual
Chrominance Bandwidth
This procedure verifies the following requirement:
Chrominance Bandwidth: Upper --3 dB Point: F
SC
+ 500 kHz, ᐔ100 kHz.
Lower -- 3 dB Point: F
SC
-- 500 kHz, ᐔ100 kHz.
1. Connect the precision 50 Ω cable to the output of the leveled sine wave
generator. Connect the other end of the cable to the 50 Ω to 75 Ω minimum-
loss attenuator, and then connect the attenuator to the VIDEO IN connector.
2. Select EXT REF from the C onfiguration menu.
3. Set the leveled sine wave generator frequency to 3.58 MHz (4.43 MHz PAL)
and adjust the amplitude control so that the circle overlays the graticule
compass rose.
4. Decrease the frequency on the leveled sine wave generator until the edge of
the circle display reaches the --3 dB (70% ) gaps on the vertical gratic ule axis.
See Figure 4--1.
Compass rose--3 dB Points
Figure 4- 1: - 3 dB marks on the vector graticule
5. Check that the frequency readout on the leveled sine wave generator is
between 2. 98 and 3. 18 MHz (3.83 and 4.03 MHz PAL).
6. Adjust the frequency on the leveled sine wave generator until the edge of the
circle display reaches the --3 dB (70%) point gaps on the horizontal graticule
axis.
7. Check that the frequency readout on the leveled sine wave generator is
between 2. 98 and 3. 18 MHz (3.83 and 4.03 MHz PAL).