Data Sheet Chapter 5

4-6 kW UHF Translator Chapter 5, Detailed Alignment Procedures
837B, Rev. 0 5-15
5.4.15 Calibration of Output Power
and VSWR Cutback of the Tray
Place a wattmeter and dummy load of at
least 600 watts at the output of the tray
that is to be calibrated and switch the
front panel meter to the % Output Power
position. Preset R16, manual gain, on
(A8) the amplifier control board fully
CCW. Move switch S1 on the amplifier
control board to the Manual position.
Insert a visual-only with a sync-only test
signal to the system and verify 40 IRE
units of sync or insert a digital test
signal. Adjust R16 for 360 watts sync-
only analog, 300 watts 64 QAM or 8-VSB
digital.
To test for analog, using zero span and
aural addition, monitor a sample of the
output with a spectrum analyzer set to
the 0 span position and adjust the
spectrum analyzer so that the level of the
output is at the top line of the graticule.
Insert -10 dB of aural to the visual sync-
only test signal and adjust R16 for the
same reference level on the spectrum
analyzer as with the visual-only input.
The output power on the wattmeter
should be approximately 550 watts visual
and -10 dB aural or 300 watts 64 QAM or
8-VSB digital. Calibrate the front panel
output power meter to 100% with R2,
forward calibration, on the amplifier
control board.
Reduce manual gain pot R16 to a 50%
reading on the front panel meter in the
% Output Power position. Turn off the
tray. Remove the load from the output
of the tray and switch the front panel
meter to the Reflected Output Power
position. Switch on the tray. Adjust
reflected power adjust pot R22 on the
amplifier control board to a 50% reading.
Then adjust R29, the VSWR threshold
cutback pot, on the amplifier control
board until the VSWR Cutback LED DS1
on the front panel just lights. This sets
up the VSWR cutback circuitry. After the
setup is completed, move switch S1 on
the amplifier control board to the
Automatic Gain Control position; this is
the normal operating position for the
switch. The UHF amplifier tray is now
aligned, calibrated, and ready for normal
operation. Repeat as needed for the
other Amplifier Trays in the System
5.5 Phase and Gain Adjustment of
the UHF Amplifier Trays in each
Amplifier Array
Switch the Translator to Standby and
switch Off the Main AC Circuit Breaker
located on each of the AC Distribution
Assemblies in the Amplifier Array
Assemblies. Switch Off all the AC Circuit
Breakers, located on the AC Distribution
Assembly, for the individual Amplifier
Trays.
1. Adjust all gain controls located on
the UHF Amplifier Trays full CCW.
2. Switch On the Main AC Circuit
Breaker for the Side A Amplifier
Array Assembly and switch On the
AC Circuit Breaker for Amplifier #1.
3. Place the Translator in Operate and
adjust the Gain control on the
Amplifier Tray for 50% output
power and adjust the Phase control
to mid range.
4. Monitor the output power of the
Translator by connecting a
Spectrum Analyzer to the Sample
Jack located on the Metering Panel.
Adjust the Spectrum Analyzer for
Zero Span operation. The power
could be monitored by watching the
meters on the panel but the power
change is easier to see on the
analyzer.
5. Turn On the AC to Amplifier Tray #2
and adjust its' output power to
50%.
6. While monitoring the output power
of the Translator, adjust the Phase
Control until the power reaches a
peak. If the Phase adjust reaches
its end of travel, add a 2 inch cable