TESTS AND ADJUSTMENTS
3-25
3
Tests and Adjustments
3.1
Transmitter Alignments and Calibration
Test Equipment required:
•
Oscilloscope general purpose
•
NM 3710 Field Test Set (with 20 dB attenuator)
•
BNC Test Cable
•
Frequency Counter RF
Carry out the alignment steps in the order outlined below:
3.1.1
RF Phase feedback adjustment
RF power
LF phase adjustment
RF power balance adjustment
RF phase combiner at I/P
SDM calibration
DDM calibration
Test DDM setting
Ident tone modulation depth
RF frequency adjustment
NOTE:
If some of the functions/parameters depart considerably from normal, then repeat the steps in
sequence once more, except steps 3.1.7.1 - 3.1.9.
3.1.1
RF Phase Feedback Adjustment
Connect the oscilloscope to the BNC test connector labelled PHASE CORR. located on the
transmitter modules.
NOTE
Set the scope's input mode to DC.
The waveform observed should take a continuous form without limiting segments or deep
notches or other discontinuities.
(Each modulator develops it's own waveform shape due to spreads in insertion phases).
The dynamic maximum point should be adjusted to approximately -4 volt.
The average operating point of the PHASE CORR signal can be shifted by means of adjusting
potentiometer PH.OFFS. at the back of the LPA/GPA (See Figure 3-6).
3.1.2
RF Power
The CSB and corresponding SBO output power can be adjusted by means of the RMM Pro-
gram or the Local Display/Keyboard.
