R3131 Spectrum Analyzer Operation Manual
2.3.4 Measuring the VA Ratio
23.4 Measuring the VA Ratio
The VA ratio is the ratio between the video signal and the audio signal used in television carriers.
When the audio signal level is too low in relation to the video signal level, bass sound is produced. In the
opposite situation, the video signal has interference caused by cross modulation from the audio signal.
Therefore, the VA ratio must be kept at a moderate level. The spectrum analyzer provides you with an easy
way to adjust this ratio.
Measurement conditions:
This example shows how to measure the VA ratio for the first UHF channel(91.25MHz).
Use appropriate parameter values to make the measurements shown below.
Setup
1. Connect the trunk amplifier as shown in Figure 2-66.
R3131 Spectrum analyzer
r
Power on
cm
..,, 13130 13
131313 0 0
.= 1030 13
1303 0
0 moms eas• 0
M 8E1E1 El
0 0 0
Impedance Converter
ZT-130NC
Trunk amplifier
0
Monitor terminal
Figure 2-66 Setup for Measuring the VA Ratio
2. Turn the power on.
Checking the trunk amplifier
3. Activate the output of the trunk amplifier.
Initialization
This resets the current settings to the factory defaults.
4. Press SHIFT and CONFIG (PRESET).
The default settings have now been reset.
Setting the measurement conditions
This activates the 75 SI mode used with an external converter.
5. Press LEVEL and Input 50 W75 a
2-71
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