User's Manual

300-Watt Digital UHF Transmitter Chapter 5, Detailed Alignment Procedures
DT830A, Rev. 1 5-1
Chapter 5
Detailed Alignment Procedures
This transmitter was aligned at the
factory and should not require additional
alignments to achieve normal operation.
This transmitter operates using a single
64-QAM or 8-VSB digital input.
Check that the RF output at J2 of (A11)
the coupler is terminated into a dummy
load of at least 300 watts. While
performing the alignment, refer to the
Test Data Sheet for the transmitter and
compare the final readings from the
factory with the readings on each of the
trays. The readings should be very
similar. If a reading is way off, the
problem is likely to be in that tray.
Switch on the main AC and the UHF
exciter circuit breakers on the AC
distribution panel behind the rear cabinet
door.
5.1 (A4) UHF Exciter Tray (1294-
1111; Appendix C)
The UHF exciter tray operates using a
digital IF input from the DT1B modulator
or other digital IF source.
The digital IF connects to J6 on the rear
of the UHF exciter, which is cabled to the
delay equalizer board, and then to the IF
relays on the ALC board. To operate
using the digital input, the modulator
select must be present. The jumper must
be connected from J11-10 and J11-28 on
the rear of the UHF exciter or jumper
W11 on J29 must be on pins 2 and 3.
To align the UHF exciter tray using the
digital IF input, apply the digital IF, with
the test signals used as needed, to the IF
input jack (J6) on the rear of the tray. In
addition, check that the modulator select
is enabled by having W11 on J29 on the
ALC board between pins 2 and 3.
Set the input matching jumper J9 to
positions 1 and 2 for a 50-Ω input, or to
positions 2 and 3 for 75Ω, on the delay
equalizer board (1072090).
Table 5-1 shows the jumper positions for
the 6-dB pad on the delay equalizer
board for an input level of between 0 to
-10 dBm.
Table 5-1. Jumper Positions on the 6-dB Pad
IF Input Range 6-dB Pad W1 on J23 & W2 on J27
-5 to 0 dBm Enable 2-3 2-3
-10 to -5 dBm Disable 1-2 1-2
The output level of the delay equalizer
board should be -11 to -6 dBm with a
response of 0.1 dB across the channel.
The IF connects to the (A8) ALC board
(1265-1305). The IF section of the UHF
exciter tray includes adjustments for
automatic level control (ALC), linearity
(amplitude pre-distortion), and phase
(phase change vs. level) pre-distortion
for correction of the non-linearities 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 require adjustments at
this time.
Move the Operate/Standby switch located
on the UHF exciter tray to Standby. The
setup of the RF output includes
adjustments to the drive level of the four
UHF amplifier trays, the adjustment of
the linearity and phase predistortion to
compensate for any nonlinear response
of the amplifier trays, and also gain and