Data Sheet Chapter 5

4-6 kW UHF Translator Chapter 5, Detailed Alignment Procedures
837B, Rev. 0 5-6
response; it may have changed with the
adjustment to the envelope delay.
5.3 UHF Exciter Tray with Receiver
Tray, or either (Optional) Baseband
or (Optional) 4.5-MHz Composite
Input
The IF section of the UHF exciter tray
includes adjustments for automatic level
control (ALC), linearity (amplitude
predistortion), and phase (phase change
vs. level) predistortion for correction of
the nonlinearities of the RF amplifier
trays. The upconverter section also
includes adjustments to the local
oscillator chain tuning and the local
oscillator center frequency tuning. Both
of these were completed at the factory
and should not need to be adjusted at
this time.
Move the Operate/Standby switch on the
UHF exciter tray to Standby. The setup of
the RF output includes adjustments to
the drive level for the UHF amplifier
trays, the adjustment of the linearity and
phase predistortion that compensate for
any nonlinear response of the amplifier
trays, and the gain and phasing
adjustments of the UHF amplifier trays.
Verify that all red LEDs on the ALC board
are extinguished. The following list
describes the meaning of each LED when
it is illuminated:
• DS1 (Input Fault) – Indicates that an
abnormally low or no IF is present at
the input of the board
• DS2 (ALC Fault) – Indicates that the
ALC circuit is unable to maintain the
signal level requested by the ALC
reference. Normally, this is due to
excessive attenuation in the linearity
signal path or the IF phase corrector
signal path or because jumper W3 on
J6 is in the Manual ALC gain position.
• DS3 (Video Loss) – Indicates a loss of
video at the input of the board
• DS4 (Mute) – Indicates that a visual
Mute command is present (not used
in this configuration)
• DS5 (Modulator Enable) – Indicates
that the modulator IF output is
selected. This LED is only used if a
receiver tray is present in the system.
DS5 is always on when there is no
receiver.
The ALC is muted when the translator is
in Standby. To monitor the ALC, check
that the on/off circuit breakers on the AC
input assembly in the rear of the
Amplifier Array Cabinets are Off and
switch the translator to Operate. Adjust
the power adjust gain pot on the front
panel of the UHF exciter tray to obtain
+0.8 VDC on the front panel meter in the
ALC position. On (A8) the ALC board,
move jumper W3 on J6 to the Manual
position, between pins 2 and 3, and
adjust R87 on the ALC board for +0.8
VDC on the front panel meter in the ALC
position. Move jumper W3 back to Auto,
between pins 1 and 2; this is the normal
operating position. The detected IF signal
level at J19-2 on the ALC board is
connected to the transmitter control
board that distributes the level to the
UHF amplifier trays. The level is used as
a reference for the automatic gain control
(AGC) in each amplifier tray.
5.3.1 (A6) (Optional) Delay Equalizer
Board (1227-1204; Appendix D)
This board has been factory tuned and
should not be retuned without the proper
equipment. If it is necessary to tune the
board:
1. Select a sinX/X test signal as the
video source to the delay equalizer
board.
2. Monitor the video output of the
board at video sample jack J2 with
a video measuring set (VM700) that
has been adjusted to measure
group delay.