TESTS AND ADJUSTMENTS
3-28
Figure 3-3 Power balance SBO illustration.
Perfect power balance between the 90 Hz modulated carrier and the 150 Hz modulated car-
rier is indicated when the two largest sets of peak waveforms fall on lines parallel to the base-
line. A more accurate way of observing a power balance error is to double the sweep rate in
non-trigger mode such that the second 60 Hz half of the cycle is folded back on the first half
and tracks the envelope waveform.
RF Power Balance can be adjusted by potentiometer RF-BAL on the back of the LPA/GPA
(See Figure 3-6). Adjust until both halves fall on the same envelope waveform or the two larg-
est sets of peak waveforms fall on lines parallel to the baseline (See Figure 3-3).
3.1.5
RF Phase at Combiner I/P
Connect the oscilloscope to the BNC test connector labelled SBO located on the transmitter
modules.
NOTE:
Set the scope's input mode to DC. Set the oscilloscope in normal trigger mode such that the
waveform below can be observed.
.
Figure 3-4 RF phase SBO illustration
The RF phase (90° start phase) can be adjusted by trimmer RF PHASE on the back of the
LPA/GPA. Adjust until the minima points between the smallest peak waveform reach the
baseline or a minimum.
DEMODULATION SBO: 1dB POWER
IMBALANCE (150Hz<90Hz)
DEMODULATION SBO: NORMAL
DEMODULATION SBO: 5° RF PHASE ERROR
DEMODULATION SBO: NORMAL
