User's Manual

Digital UHF Transmitter Chapter 5, Detailed Alignment Procedures
DT835A, Rev. 1 5-4
5.2.2 IF Phase Corrector Adjustment
As shipped, the exciter was preset to
include linearity (gain vs. level) and
phase pre-distortion. The pre-distortion
was adjusted to approximately
compensate the corresponding non-linear
distortions of the amplifier trays.
Locate (A9) the IF phase corrector board
(1227-1250) mounted in the UHF exciter
tray. Because the amplitude correction
portion of the board is not utilized in this
configuration, the jumper W3 on J10
should be in the disable position and R35
and R31 should be fully counter-
clockwise (CCW). R68 is the range
adjustment and should be set in the
middle. The phase correction
enable/disable jumper W2 on J9 should
be in the Enable position to ground.
Set up a spectrum analyzer with 30 kHz
resolution bandwidth and 30 kHz
modulation bandwidth to monitor the
intermodulation products of the RF
output signal. A typical digital spectrum
is shown in Figure 5-1. There are three
corrector stages on the IF phase
corrector board, each with a magnitude
and a threshold adjustment which are
adjusted as needed to correct for any
intermod problems. Adjust the R3
threshold for the cut in point of the
correction and the R7 magnitude for the
amount of the correction that is needed.
The jumper W1 on J8 is set to give the
desired polarity of the correction shaped
by the threshold R11 and magnitude R15
adjustments. After setting the polarity,
adjust the R11 threshold for the cut in
point of the correction and the R15
magnitude for the amount of the
correction that is needed. Finally, adjust
the R19 threshold for the cut in point of
the correction and the R23 magnitude for
the amount of the correction that is
needed. The above pots are adjusted for
the greatest separation between the
digital signal and the intermod at the
channel edges.
Figure 5-1: Typical Digital Spectrum