UBS Axcera LU1000AT 1000-Watt UHF Transmitter User Manual 379383

UBS-Axcera 1000-Watt UHF Transmitter 379383

Chapter 5 Exciter

UHF Analog Driver/Transmitter Chapter 5, Detailed Alignment Procedures
LX Series, Rev. 0 5-1
Chapter 5
Detailed Alignment Procedures
This transmitter was aligned at the
factory and should not require additional
adjustments to achieve normal operation.
This transmitter takes the baseband
audio and video inputs or, if the
(Optional) 4.5-MHz composite input kit is
purchased, either a single composite
video + 4.5-MHz input or separate
baseband video and audio inputs, and
converts them to the desired UHF On
Channel RF Output at the systems output
power level.
The exciter/amplifier of the LX Series
transmitter is of a Modular design and
when a Module fails that module needs to
be changed out with a replacement
module. The failed module can then be
sent back to Axcera for repair. Contact
Axcera Customer Service Department at
724-873-8100 or fax to 724-873-8105,
before sending in any module.
5.1 Module Replacement
Module replacement on the LX series
products is a relatively simple process.
All modules plug directly into the
backplane board except for the power
amplifier module, and in higher power
units, the power supply and power
amplifier modules, that plug into a blind
mating connector. To replace a module,
refer to the following procedure.
Loosen the two grip lock connectors,
located on the front panel, at the top
and bottom of the module,
counterclockwise until the module
releases. The Modulator, IF Processor,
Upconverter and Controller/Power
Supply can then be gently pulled from
the unit. There are two cables
connected to the rear of the Power
Amplifier Module in the exciter/amplifier
chassis assembly. These two cables
must first be removed before the PA
module will slide out.
After removal of the failed module, slide
the replacement module in place and
make certain it connects to the
backplane board. If the replacement
module is a PA Module replace the two
cables on the rear of the
exciter/amplifier chassis assembly. If
the replacement module does not slide
in easily, verify it is properly aligned in
the nylon tracks, located on both the top
and bottom of the module.
Note: Each Module has an assigned slot
and will not fit properly in the incorrect
slot. Do not try to place a Module in the
wrong slot as this may damage the slot
or the connectors on the backplane
board.
Each module has the name of the
module on the front, bottom for
identification and correct placement.
The Modules are placed in the unit from
left to right; (1) Blank panel, (2)
Modulator (for analog transmitters) or a
Blank panel for a Translator or digital
transmitter, (3) IF Processor, (4)
Upconverter, (5) Controller/Power
Supply and (6) Power Amplifier.
5.1.1 Initial Test Set Up
Check that the RF output at the coupler
is terminated into a dummy load of at
least 100 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 modules. The
readings should be very similar. If a
reading is way off, the problem is likely
to be in that module.
Switch On the main AC for the system.
UHF Analog Driver/Transmitter Chapter 5, Detailed Alignment Procedures
LX Series, Rev. 0 5-2
5.2 LX Series Exciter/Amplifier
Chassis Assembly
This transmitter operates using the
baseband audio and video inputs or, if
the (optional) 4.5-MHz composite input
kit is purchased, either a single
composite video + 4.5-MHz input or
separate baseband video and audio
inputs.
On the LCD Display, located on the
Controller/Power Supply Module, in
Transmitter Set-Up, push the button to
switch the transmitter to Operate. The
check of and the setup of the Audio and
Video input levels are completed using
the LCD Display and the front panel
adjustments on the Modulator assembly.
The level of the RF output includes
adjustments of the drive level to the
Power Amplifier and the adjustment of
the linearity and phase predistortion to
compensate for any nonlinear response
of the Power Amplifier. The adjustments
are located on the front panel of the IF
Processor module.
Modulator Module Assembly
NOTE: Not present in a Translator
systems.
The Modulator Assembly has adjustments
for video levels and audio modulation
levels, and other related parameters.
Connect an NTSC baseband video test
signal input (1 Vpk-pk) to the transmitter
video input jack J7 on the rear of the
tray. Jacks J7 and J17 are loop-through
connected; the J17 jack can be used as a
video source for another transmitter.
Connect a baseband audio input (+10
dBm) to the balanced audio input
terminal block TB02-1 [+], TB02-2 [-],
and TB02-3 [ground] or, if
stereo/composite audio is provided,
connect it to BNC jack J3, the composite
audio input jack.
Verify that all LEDs located on the front
panel of the Modulator are Green. The
following details the meaning of each
LED:
AURAL UNLOCK (DS5) – Red Indicates
that 4.5 MHz Aural IF is unlocked from
the Nominal 45.75 MHz visual IF.
VISUAL UNLOCK (DS6) – Red Indicates
that the Nominal 45.75 MHz visual IF is
unlocked from the 10 MHz reference.
AUDIO OVER DEVIATION (DS4) – Red
Indicates that the input Audio level is too
high. (±75 kHz max)
VIDEO LOSS (DS1) – Red Indicates that
the input Video level is too low.
OVER MODULATION (DS3) – Red
Indicates that the input Video level is too
high.
ALTERNATE IF (DS7) – Red Indicates
that an external Nominal 45.75 MHz IF is
not present to the modulator.
10 MHz PRESENT (DS2) – Red Indicates
that an external 10 MHz reference is not
present to the modulator.
Look at the front panel LCD meter on the
Control/Power Supply Module Assembly.
Set the LCD screen to the Modulator
Details video output level screen, the
screen indicates active video from 0 to 1
Vpk-pk. The normal video input level is 1
Vpk-pk on the front panel screen. If this
reading is not at the proper level, the
overall video level can be changed by
adjusting the VIDEO LEVEL control R42
on the front panel of the Modulator to the
1 Vpk-pk level on the front panel screen.
NOTE: An NTSC or FCC composite signal
should be used for video metering
calibration.
Switch the LCD display to the Modulator
Details screen that indicates the AUDIO
DEVIATION (modulation level) of the
signal up to 75 kHz.
UHF Analog Driver/Transmitter Chapter 5, Detailed Alignment Procedures
LX Series, Rev. 0 5-3
MONO SET UP: The modulator was
factory set for a ±25-kHz deviation with
a mono, balanced, audio input of +10
dBm. If the reading is not at the correct
level, adjust the MONO Audio Gain pot
R110, located on the front panel of the
modulator, as necessary, to attain the
±25-kHz deviation on the front panel
screen.
STEREO SET UP: The modulator was
factory set for a ±75-kHz deviation with
a stereo, composite, audio input of 1
Vpk-pk. If this reading is not correct,
adjust the STEREO Audio Gain pot R132,
located on the front panel of the
modulator, as necessary, for the ±75-
kHz deviation.
SECONDARY AUDIO SET UP: NOTE:
Remove any stereo or mono audio
modulation input to the transmitter
during the set up of the secondary audio.
The modulator was factory set for a ±15-
kHz deviation with a secondary audio
input of 1 Vpk-pk. If this reading is not
correct, adjust the SAP/PRO Audio Gain
pot R150, located on the front panel of
the modulator, as necessary, for the
±15-kHz deviation.
IF Processor Module Assembly
Verify that all red LEDs located on the IF
Processor front panel 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 IF
Processor module.
• 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 switch SW1 is in
the Manual ALC Gain position.
• DS4 (Mute) – Indicates that a Mute
command is present to the system.
Switch the transmitter to Standby. The
ALC is muted when the transmitter is in
Standby. To monitor the ALC, preset R3,
the manual gain adjust pot, located on
the front panel of the Upconverter
module, fully CCW. Move switch SW1,
Auto/Man AGC, on the front panel of the
Upconverter module, to the Manual
position. Place the transmitter in
Operate. Adjust the ALC GAIN pot on the
front panel of the IF Processor to obtain
100% output power on the LCD Display
mounted on the Controller/Power Supply
in the ALC screen. Move the MAN/AUTO
ALC switch back to Auto, which is the
normal operating position.
To adjust the AGC Cutback setting, raise
the output power of the transmitter to
120%. Adjust R2, AGC Cutback, located
on the front panel, CCW until the LED
DS1, AGC Cutback, just starts to flash.
Return the output power of the
transmitter to 100%.
5.2.1 Linearity Correction
Adjustment
As shipped, the exciter was preset to
include amplitude and phase pre-
distortion. The pre-distortion was
adjusted to approximately compensate
the corresponding non-linear distortions
of the Power Amplifier.
NOTE: On the IF processor board inside
the module the correction enable/disable
jumper W12 on J30 will be in the Enable
position, on pins 2 & 3.
Set up a spectrum analyzer with 100
kHz resolution bandwidth and 100 kHz
video bandwidth to monitor the
intermodulation products of the RF
output signal of the Power Amplifier.
A typical red field spectrum is shown in
Figure 5-1. There are three Linearity
Corrector stage adjustments located on
the front panel of the IF Processor
UHF Analog Driver/Transmitter Chapter 5, Detailed Alignment Procedures
LX Series, Rev. 0 5-4
Module. The adjustments are threshold
settings that are adjusted as needed to
correct for any amplitude or phase
intermod problems. Adjust the top
linearity correction adjustment R211
threshold cut in for the in phase
amplitude distortion pre-correction that
is needed. Next adjust the middle
linearity correction adjustment R216
threshold cut in also for the in phase
amplitude distortion pre-correction that
is needed. Finally adjust the bottom
linearity correction adjustment R231
threshold cut in for the quadrature
phase distortion pre-correction that is
needed. The above pots are adjusted
for the greatest separation between the
peak visual carrier and the intermod
products. NOTE: These pots affect
many other video parameters, so care
should be taken when adjusting the
linearity correction.
Figure 5-1. Typical Red Field Spectrum
5.2.2 Frequency Response Delay
Equalization Adjustment
The procedure for performing a
frequency response delay equalization
adjustment for the transmitter is done at
IF and is described in the following steps:
The center frequency for the first stage is
45 MHz. Adjust R103, the top frequency
response equalizer pot, located on the
front panel of the IF Processor Module,
for the best depth of frequency response
correction at 45 MHz.
The center frequency for the second
stage is 42 MHz. Adjust R106, the
middle frequency response equalizer pot,
located on the front panel of the IF
Processor Module, for the best depth of
frequency response correction at 42 MHz.
The center frequency for the second
stage is 43.5 MHz. Adjust R274, the
bottom frequency response equalizer pot,
located on the front panel of the IF
Processor Module, for the best depth of
frequency response correction at 43.5
MHz.
After the three delay attenuation
equalizers have been adjusted, fine tune,
as needed, for the best frequency
response across the channel.
5.2.3 Calibration of Output Power
and Reflected Power of the
transmitter
Note: Perform the following
procedure only if the power
calibration is suspect.
Switch the transmitter to Standby and
place the Upconverter into Manual Gain.
Preset R205, the aural null pot on the
Amp Control board, fully CCW. Adjust
R204, the null offset pot on the Amp
UHF Analog Driver/Transmitter Chapter 5, Detailed Alignment Procedures
LX Series, Rev. 0 5-5
Control board, for 0% visual output.
Perform the following adjustments with
no aural present by removing the aural
IF carrier jumper on the back of the
chassis assembly. Connect a sync and
black test signal to the video input jack
of the test modulator. Switch the
transmitter to Operate.
Next, set up the transmitter for the
appropriate average output power level:
Example is for 100 Watt Transmitter.
• Sync + black 0 IRE
setup/wattmeter=59.5 watts
• Sync + black 7.5 IRE
setup/wattmeter=54.5 watts
Note: The transmitter must have 40
IRE units of sync.
Adjust R202, visual calibration, on the
Amp Control board for 100% on the front
panel LCD display in the % Visual Output
position.
With the spectrum analyzer set to zero
span mode, obtain a peak reference on
the screen. Reconnect the aural carrier
jumper on the rear of the chassis
assembly. Turn the power adjust pot on
the front panel until the original peak
reference level is attained. Adjust R203
for a 100% aural power reading. Switch
to the Visual Output Power position and
adjust R205 (aural null pot) for 100%
visual power.
To calibrate the reflected output power
reading of the transmitter. Reduce
manual gain pot R3 to a 10% reading on
the LCD front panel display in the %
Output Power position. Place the
transmitter in Standby. Remove the PA
Module Sled. Remove the load from J4
on the (A4) Directional Coupler Board
and switch the LCD Display screen to the
Reflected Output Power position.
Reinstall the PA Module. Switch the
transmitter to operate. Adjust the
reflected power calibration adjust pot
R163 on the power amplifier module to a
10% reading. A reflected power fault
should be present on the LCD Display.
Reconnect the load to J4 in the module.
After this calibration is completed, move
switch SW1 on the upconverter module
to the Automatic AGC position. This is
the normal operating position for the
switch. Adjust the ALC pot on the IF
Processor is needed to attain 100%
output power. Switch to Manual Gain
(Manual AGC) and adjust the Manual
Gain pot for 100 % output power.
Switch the upconverter back to
Automatic AGC.
The Transmitter is now aligned,
calibrated, and ready for normal
operation.
This completes the detailed alignment
procedures for the LX Series transmitter.
If a problem occurred during the
alignment, help can be found by calling
Axcera field support at 724-873-8100.
5.3 Alignment Procedure for the
Bandpass Filter Assembly
The Bandpass Filter Assembly is tuned to
reject unwanted distortion products
generated when the signals are diplexed
and also during the amplification process.
The Bandpass Filter is factory tuned to
the proper bandwidth and should not
need tuned. If you think tuning is
needed consult Axcera Field Support
Department before beginning the
adjustment.
The Traps are labeled with their Center
Frequency relative to the Frequency of
the Carrier. (For Example: The Traps
labeled -4.5 MHz are tuned for a Center
Frequency of 4.5 MHz Lower than the
Frequency of the Visual Carrier.)
The Trap Sections are Reflective Notches,
adjustable across the entire UHF
Frequency Band. The electrical length of
UHF Analog Driver/Transmitter Chapter 5, Detailed Alignment Procedures
LX Series, Rev. 0 5-6
the Outer Sleeve and the Center Rod of
the Notch can be adjusted to tune the
Notch Frequency. The Depth of the
Notch is set by the gap between the
Center Conductor of the Trap Section and
the Center Conductor of the Main Line.
Tight Coupling makes a Deep Notch,
while Loose Coupling makes a Shallow
Notch.
NOTE: The Trap Sections have been
factory tuned and should not need major
adjustments. The Frequency, relative to
Visual Carrier, that the Trap is tuned to is
marked on the Notch. Fine Tuning of the
Notches Center Frequency can be
accomplished with the Tuning Bolts
located on the side of the Filter Section.
Loosen the nut locking the Bolt in place
and adjust the Bolt to change the
Frequency of the Notch. Monitor the
output of the Transmitter with a
Spectrum Analyzer and Null the
Distortion Product with the Bolt.
Red Field is a good Video Test Signal to
use to see the out-of-band Products.
Tighten the nut when the tuning is
completed. Hold the bolt in place with a
screwdriver as the nut is tightened to
prevent it from slipping.
For major tuning, such as changing the
Notch Depth or moving the Notch
Frequency more than 1 MHz, the Outer
Conductor and the Center Conductor of
the Trap Section must both be moved.
This requires an RF Sweep Generator to
accomplish. Apply the Sweep signal to
the Input of the Trap Filter and monitor
the Output. Loosen the Clamp holding
the Outer Conductor in place and make
the length longer to Lower the frequency
of the Notch or shorter to Raise the
frequency of the Notch. Loosen the
Center Conductor with an Allen Wrench
and move it Deeper for a Lower
Frequency Notch or out for a Higher
Frequency Notch. These adjustments
must both be made to change the Notch
Frequency. Moving only the Center
Conductor or the Outer Conductor will
effect the Notch Depth in addition to the
Center Frequency. The variable that is
being adjusted with this procedure is the
length of the Center Conductor inside the
Trap Filter. The gap between the Trap
and the Main Line should not be changed.
Moving only the Inner or the Outer
Conductors by itself will effect the Gap
and the Notch depth.
To effect the Notch Depth Only, both
sections will have to be moved. The
Notch Depth is controlled by the Gap
between the Center Conductor and the
Trap Section. This Gap also has an effect
on the Center Frequency. To Deepen the
Notch, Shorten the Outer Conductor and
pull the Center Conductor Out until the
Notch is back in the same place. Move
the Sections in the opposite direction to
make a Shallow Notch.
After tuning has been completed, tighten
the Clamp and the Allen Screws which
hold the Conductors. Use the Fine
Tuning Bolts to bring the Frequency In.
The Final Tuning Adjustments should be
completed with the Transmitter driving
the Output Trap Filter for at least one
hour to allow for warm-up drift.
This completes the Alignment Procedure
for the Bandpass Filter Assembly and the
exciter/amplifier assembly of the LX
Series Transmitter.

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