UBS Axcera LU1000AT 1000-Watt UHF Transmitter User Manual 379393

UBS-Axcera 1000-Watt UHF Transmitter 379393

Chapter 5 External Amplifier

LX Series Power Amplifier Assembly Chapter 5, Detailed Alignment Procedures
LX Series, Rev. 0 5-1
Chapter 5
Detailed Alignment Procedures
This Power Amplifier Assembly along with
the 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 power amplifier assembly of the
Innovator 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.
The power supply and power amplifier
modules, plug into a blind mating
connector located on the chassis. 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. There are two cables
connected to the rear of the Power
Amplifier Module. 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 blind
mate connector. Replace the two cables
on the rear of the 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 blind mate connectors.
5.1.1 Initial Test Set Up
Check that the RF output at the coupler
is terminated into a dummy load of at
least the rated output of the system.
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.
5.2 Innovator 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
LX Series Power Amplifier Assembly Chapter 5, Detailed Alignment Procedures
LX Series, Rev. 0 5-2
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: The Modulator Assembly is not
present in a translator system.
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 45.75 MHz visual IF.
VISUAL UNLOCK (DS6) – Red Indicates
that the 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.
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 45.75 MHz IF is not
present to the modulator.
10 MHz PRESENT (DS2) – Red Indicates
that an external 10 MHz reference in 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.
Switch the LCD display to the Modulator
Details screen that indicates the AUDIO
DEVIATION (modulation level) of the
signal from 0 to 100 kHz.
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
LX Series Power Amplifier Assembly Chapter 5, Detailed Alignment Procedures
LX Series, Rev. 0 5-3
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
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.
LX Series Power Amplifier Assembly Chapter 5, Detailed Alignment Procedures
LX Series, Rev. 0 5-4
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
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 43.5 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 43.5
MHz.
The center frequency for the second
stage is 42 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 42 MHz.
After the three delay attenuation
equalizers have been adjusted, fine tune,
as needed, for the best frequency
response across the channel.
Note: The frequency response
adjustment is done at IF, so the
frequency cut-in points will be
reversed at the UHF frequencies.
5.2.3 Calibration of the Transmitter
Forward Output Power Level
Note: Perform the following
procedure only if the power
calibration is suspect.
Switch the transmitter to Standby and
preset R51, the aural null pot on (A4) the
visual/aural metering board, fully CCW.
Switch the LO/Upconverter sled to
Manual Gain. Adjust R48, the null offset
pot on the visual/aural metering board,
full CW. Adjust CCW until 0% visual
output is displayed on the LCD Display in
the System Visual Power position.
Perform the following adjustments with
no aural present by removing the jumper
cable, the aural IF loop-through, that is
connected on the rear of the
exciter/driver chassis. Connect a sync
and black test signal to the video input
jack of the exciter/driver. Switch the
transmitter to Operate.
Next, set up the transmitter for the
appropriate average output power level
using the Manual Gain pot on the
LO/Upconverter sled:
LX Series Power Amplifier Assembly Chapter 5, Detailed Alignment Procedures
LX Series, Rev. 0 5-5
Example is for 1000 Watt transmitter.
• Sync + black 0 IRE
setup/wattmeter=595 watts
• Sync + black 7.5 IRE
setup/wattmeter=545 watts
Note: The transmitter must have 40
IRE units of sync.
Adjust R28, visual calibration, on the
(A4) visual/aural metering board for .8V,
at TB30-14 and TB30-12 return, on the
exciter/driver assembly, then adjust
display to read 100% on the front panel
meter in the System Forward Power
position.
With the spectrum analyzer set to zero
span mode, obtain a peak reference on
the screen. Reconnect jumper cable on
the rear of the exciter/driver. While in
the Visual Output Power position, adjust
L3 for a minimum visual power reading
on the LCD display. Turn the power
adjust pot on the LO/Upconverter sled
front panel until the original peak
reference level is attained. Peak L1 and
C8 for a maximum aural power reading,
then adjust R20 for .8V, at TB30-15 and
TB30-12 return, on the exciter/driver
assembly, then adjust LCD display for
100% system aural power reading.
Switch to the Visual Output Power
position and adjust R51 for 100% visual
power on system LCD display.
5.2.4 Calibration of the Transmitter
Reflected Output Level
On the meter, in the Visual Power
position, turn the power adjust pot to
25%. Move the Reflected cable on the
(A11) coupler to the unused “INC” port
on the coupler. Then adjust R39 on (A4)
the visual/aural metering board for a
.2VDC, at TB30-13 and TB30-12 return,
on the exciter/driver assembly. Then
adjust the LED display for 25% reading in
the System Reflected Power position. At
this 25% reference power reading a
reflected power fault should appear on
the System Errors Menu. Turn the power
adjust pot slightly CCW and the fault
should be clearable on the System Error
Menu. Turn the pot CW until the Fault
appears. The reflected output power is
now calibrated.
Switch the transmitter to Standby and
move the Reflected power cable on the
A11 Coupler back to the “Reflected Port”.
Switch the transmitter to Operate and
adjust the front panel power pot for a
100% visual power reading. Switch the
LO/Upconverter to the Auto AGC position
and adjust the ALC Gain adjust pot on
the front of the IF Processor module for
100% visual power reading, if needed.
5.3 (A9) 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.
5.4 (A10) UHF Trap Filter Assembly
The Traps on the output Trap Filter 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 first section of the
Trap Filter filters out the Visual Carrier
plus 9 MHz (fv+9 MHz). The second and
fourth sections work together to filter out
the lower spurious product (fv-4.5 MHz).
The third section is tuned to remove the
(fv+8.08). The output of the Trap Filter
is an "N" Type Connector.
The Trap Sections have been factory
tuned and should not need major
LX Series Power Amplifier Assembly Chapter 5, Detailed Alignment Procedures
LX Series, Rev. 0 5-6
adjustments. The Trap Filter is
comprised of four trap sections
connected to the main transmission line.
The Trap Sections are Reflective Notches,
adjustable across the entire UHF
Frequency Band. The electrical length of
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.
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 +8.08 MHz Product. 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.
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 a 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. NOTE: THE
TRAP FILTER IS TYPICALLY ADJUSTED
FOR A NOTCH DEPTH OF 10 dB.
5.4.1 The Effects of Tuning the
Output Trap Filter
Lengthening Outer Conductor Only -
Notch Frequency Up, Shallower Notch.
Shortening Outer Conductor Only - Notch
Frequency Down, Deeper Notch.
Inserting Inner Conductor Deeper - Notch
Frequency Down, Deeper Notch.
Inserting Less Inner Conductor - Notch
Frequency Up, Shallower Notch.
Tuning Bolt In - Notch Frequency Down.
Tuning Bolt Out - Notch Frequency Up.
Moving both Inner and Outer Conductors
to keep the Same Gap inside - Center
Frequency Moves, Notch Stays the Same.
After tuning has been completed, tighten
the Clamp and the Allen Screws that hold
the Conductors. Use the Fine Tuning
Bolts to bring the Frequency In. The
Final Tuning Adjustments should be
completed with the Transmitter driving
LX Series Power Amplifier Assembly Chapter 5, Detailed Alignment Procedures
LX Series, Rev. 0 5-7
the Output Trap Filter for at least one
hour to allow for warm-up drift.
The Transmitter is 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.

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