Data Sheet Chapter 5

4-6 kW UHF Translator Chapter 5, Detailed Alignment Procedures
837B, Rev. 0 5-19
Return CB1, the Main AC circuit breaker
for the Side A Amplifier Array, to the On
position.
5.12 IF Phase Corrector Adjustment
of the Translator
As shipped, the exciter was preset to
include linearity (gain vs. level) and
phase (phase vs. level) predistortion. The
predistortion was adjusted to
approximately compensate the
corresponding non-linear distortions of
the amplifier trays and should not require
additional adjustments.
Locate (A9) the IF phase corrector board
(1227-1250) mounted in the UHF exciter.
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, to +6.8
VDC, and R35 and R31 should be fully
CCW. R68 is the range adjustment and
should be set in the middle of the range.
The phase correction enable/disable
jumper W2 on J9 should be in the enable
position to ground.
Switch the video input test source to
select an NTSC 3.58-MHz modulated
staircase or ramp test waveform and set
up the station demodulator and
monitoring equipment to monitor the
differential phase or intermodulation
products of the RF output signal. There
are three corrector stages on the IF
phase corrector board, each with a
magnitude and a threshold adjustment,
that are adjusted as needed to correct for
any differential phase or intermodulation
problems. If necessary, adjust the R3
threshold for the cut-in point of the
correction and the R7 magnitude for the
amount of the correction.
Jumper W1 on J8 is set to give the
desired polarity of the correction that has
been 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.
Note: Adjusting these pots changes
all visual parameters and should be
done cautiously.
On the IF phase corrector board (1227-
1250), preset pots R7, R15, R23, and
R35 fully CW and R3, R11, R19, and R31
fully CCW.
Set the waveform monitor to differential
step filter and the volts/division scale to
.1 volt. Center the display around
blanking.
Gradually adjust pots R3, R11, and R19
CW, as needed, on the IF phase corrector
board to minimize the observed thickness
of the intermodulation as seen on the
display.
While performing the preceding
adjustments, the intermodulation beat
products between the colorburst and the
aural carrier at 920 kHz above visual
carrier should be observed on the
spectrum analyzer. The frequency will
vary for different video systems. When
the adjustments are performed properly,
the intermodulation products on the
spectrum analyzer should be at least -52
dB down, with a red field input, from
peak visual carrier. The intermodulation
distortion, as displayed on the waveform
monitor, should be no more than 1 unit
of IRE. The pot R31 on the IF phase
corrector board is used for any extra
intermodulation corrections that may be
needed.
Note: Any adjustment to the above
pots affects other visual parameters
and some slight adjustments to all of
the pots may be needed to
simultaneously meet all of the
specifications.