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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

+ 500 kHz, 100 kHz.

Lower --3 dB P oint: F

-- 500 kHz, 100 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 Configuration 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 graticule 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).

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Monitor Audio Vector Manuel de service Page 76