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Chapter 6
Maintenance
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- 6.9 -
E-2
4
Adjustment of I/Q Modulator
Note
The transmitter must have been in operation for at least 30 minutes before adjustment is
performed (operating temperature).
performed (operating temperature).
Objective
If quadrature modulation were optimal (theoretically possible), the residual carrier would be
completely suppressed. In actual practice, however, residual carriers arise (e.g. due to
crosstalk). They must be suppressed using suitable correction carriers.
completely suppressed. In actual practice, however, residual carriers arise (e.g. due to
crosstalk). They must be suppressed using suitable correction carriers.
The objective of I/Q adjustment is to suppress the undesired center carrier and undesired
carrier in the sideband with respect to a test carrier by better than 60 dB.
carrier in the sideband with respect to a test carrier by better than 60 dB.
4.1
Manual Adjustment
Preparation and test carrier measurement
1. Call the TV Settings > RF Out > IQ Adjust menu.
2. Switch on the test signal using the I/Q Testsignal switch.
3. Connect a spectrum analyzer to the
RF MONITOR
output on the front panel of the trans-
mitter and select the following settings:
Center Frequency
Frequency of the vision carrier
Span
6 MHz
Resolution BW
30 kHz
Video BW
300 Hz
Sweep
coupled