Technical Handbook

Table Of Contents
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Adjust 90 Hz CLR phase adj. R179 (LF1223A) observing oscilloscope channel B until the
waveform equals left hand graph in Figure 7-2.
A significant indication of correct LF phase is that the pair of the intermediate peaks are equal
in amplitude.
7.3.4 RF Power Balance Adjustment
Connect the oscilloscope to the BNC test connector labelled SBO located on the transmitter
modules.
NOTE:
Set the scope’s input mode to DC
.
Figure 7-5 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.
Adjust until both halves fall on the same envelope waveform or the two largest sets of peak
waveforms fall on lines parallel to the baseline.
NOTE:
Changes in DDM as a result of RF power balance adjustment should be compensated with
the 90Hz and 150Hz potentiometers at the back of the LPA / GPA.
7.3.5 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.
DEMODULATION SBO: 1dB POWER
IMBALANCE (150Hz<90Hz)
DEMODULATION SBO: NORMAL