User's Manual

Digital UHF Transmitter Chapter 5, Detailed Alignment Procedures
DT835A, Rev. 1 5-2
Table 5-3: 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
5.2 (A4) UHF Exciter Tray (1294-
1111; Appendix C)
The UHF exciter tray operates using the
digital IF output from the DM8-R
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 5-3 shows the jumper
positions for the 6-dB pad on the
delay equalizer board for an input
level of between 0 to -10 dBm.
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
adjustment to the drive level of the
amplifier arrays, the adjustment of the
linearity and phase predistortion to
compensate for any nonlinear response
of the amplifier trays, and also gain and
phasing adjustments to the UHF amplifier
trays.
Verify that all red LEDs on the ALC board
are extinguished. The following details
the meaning of each LED when
illuminated:
• DS1 (input fault) – Indicates that
either 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. This is normally due to
excessive attenuation in the linearity
signal path or the IF phase corrector
signal path, or that jumper W3 on J6
is in the Manual ALC Gain position.
• DS3 (modulation loss) – Indicates a
loss of modulation at the input of the
board
• DS4 (Mute) – Indicates that a Visual
Mute command is present (DS4 is not
used in this configuration.)
• DS5 (modulator enable) – Indicates
that the modulator IF output is
selected. This is only used if a