UBS Axcera 420A Low Power Television User Manual Chapter 4

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Document Title	Chapter 4

100 Watt High Band VHF Transmitter
Chapter 4, Detailed Alignment Procedures
Chapter 4
Detailed Alignment Procedures
If this transmitter contains the (optional)
4.5 MHz composite input kit, the
baseband video input is used when the
baseband video is connected to J2 and a
baseband select is connected to J18 pins
6 and 7 on the rear of the tray.
Note: J13 is a loop-through
connected to J3. It can be used as a
composite audio source if the jumper
W4 on J12 of the aural IF
synthesizer board is removed.
The baseband audio is not used with the
(optional) 4.5 MHz composite input.
Check that the RF output at J15 of the
transmitter 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 meter readings on the
tray. They should be very similar. If a
reading is more than 10% different, a
problem with the tray may exist. Switch
on the on/off AC circuit breaker on the
rear of the tray.
Observe the front panel meter on the
tray. In the video position, the meter
indicates active video from ≅ 0.3V to
1.0V. With an input video of 1 Vpk-pk,
the display should indicate 100 IRE units
at white. If the reading is at not the
proper level, the overall video level can
be changed by adjusting the video level
control (R15) on (A5) the sync tip
clamp/modulator board (1265-1302).
4.1 Alignment of the 420A
Transmitter
Switch the meter to the audio position
that will indicate the audio deviation
(modulation level) of the signal; the
meter indicates from 0 to 100 kHz. The
aural IF synthesizer board was factory
set for ±25 kHz deviation with a balanced
audio input of +10 dBm. If the reading is
not the correct level, adjust the balanced
audio gain pot R13 on the aural IF
synthesizer board, as needed, to attain
the ±25 kHz deviation. The aural IF
synthesizer board was factory set for
±75 kHz deviation with a composite
audio input of 1 Vpk-pk. If the reading is
not correct, adjust the composite audio
gain pot R17 on the aural IF synthesizer
board, as needed, for the ±75 kHz
deviation.
4.1.1 Baseband Section
This tray has adjustments for video and
audio modulation levels and other related
parameters.
Connect an NTSC composite video test
signal input (1 Vpk-pk) or an (optional)
4.5 MHz composite input to the
transmitter video input jack J2 on the
rear of the tray.
Note: J2 is a loop-through connected
to J1. It can be used as a baseband
video source if the jumper W1 on J3
of the sync tip clamp/modulator
board is removed.
Connect the baseband audio, if it is
balanced audio (+10 dBm), to the
terminal block (TB1) or connect the
composite audio (stereo) (1 Vpk-pk) to
the BNC jack (J13).
420A, Rev. 0
4-1
100 Watt High Band VHF Transmitter
Chapter 4, Detailed Alignment Procedures
4.1.2 IF/Upconverter Section
•
The upconverter section of the tray
includes adjustments for automatic level
control (ALC), linearity (amplitude predistortion), and incidental phase (phase
change vs. level) pre-distortion for
correction of the non-linearities of the RF
amplifier section of the tray. The
upconverter section also includes
adjustments to the local oscillator chain
tuning and the local oscillator center
frequency tuning. Both of these
alignments were completed at the factory
and should not need to be adjusted at
this time. Move the Operate/Standby
switch located on the front panel of the
tray to Standby.
Check that the jumper W3 on J6 of (A8)
the ALC board (1265-1305) is in the Auto
position and adjust the power gain pot
(R1) on the front panel of the tray to
obtain +0.85 VDC on the front panel
meter in the ALC position. Move the
jumper W3 on J6 to the Manual position
and adjust R87 on the ALC board for
+0.85 VDC on the front panel meter in
the ALC position. Move the jumper back
to Auto; this is the normal operating
position. The detected IF signal level at
J19-2 of the ALC board is connected to
the transmitter control board. This signal
supplies the voltage to the high-band
mixer/amplifier board where it is used as
an automatic gain control (AGC) for the
RF output signal of the upconverter
section in the amplifier section of the
tray.
The set-up of the RF output includes an
adjustment to the drive level of the
amplifier section of the tray, the
adjustment of the linearity, and the
(optional) incidental phase predistortion
which compensate for any nonlinear
response of the amplifier section.
4.1.3 Amplifier Section of the Tray
Note: Power is applied to the
amplifier boards when the
transmitter is switched to Operate.
Verify that all red LEDs on the ALC board
are extinguished. The following list
details the meaning of each LED when
illuminated:
•
DS1 (Input fault) – Indicates that
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 due to excessive
attenuation in the linearity or ICPM
corrector signal path or that jumper
W3 on J6 is in the Manual ALC Gain
position
•
DS3 (Video loss) - Indicates a loss of
video at the input of the board
•
DS4 (Visual mute) - Indicates that a
Visual Mute command is present (The
visual mute is not used in this
system.)
420A, Rev. 0
DS5 (Modulator Enable) - Indicates
that the modulator output is selected
Switch the transmitter to Operate and
verify that the visual power reading on
the front panel meter is 100%. If not,
adjust the front panel power adjust pot
to achieve 100%.
Switch the input video test source to
select an NTSC 3.58 MHz modulated
staircase or ramp test waveform. Set up
the station demodulator and monitoring
equipment to monitor the differential
gain and phase of the RF output signal.
If a synchronous demodulator having a
quadrature video output is available, it
can be used with an X-Y oscilloscope to
display incidental carrier phase
modulation (ICPM). As shipped, the
exciter was preset to include linearity
(gain vs. level) and incidental phase
(carrier phase vs. level) predistortion.
The predistortion was adjusted to
approximately compensate the
4-2
100 Watt High Band VHF Transmitter
Chapter 4, Detailed Alignment Procedures
corresponding non-linear distortions of
the amplifier that is driven to place the
sync level near saturation.
stretch the signal above the white region.
Back off on the corresponding magnitude
control R13 as required. Next, advance
the second threshold control R37 to
stretch the signal above the black range
and then back off on the magnitude
control R18 as required. Adjust the third
threshold pot R40 to stretch sync. Back
off on the corresponding magnitude
control R23 as required. Go back through
the white through black and sync
correctors to touch up the effects of ALC
level changes resulting from the
adjustment.
4.1.4 Linearity Corrector Adjustment
The IF linearity correction function
consists of three non-linear cascaded
stages, each having adjustable
magnitude and threshold, or cut-in,
points. The threshold adjustment
determines at what IF signal level the
corresponding corrector stage begins to
increase gain. The magnitude adjustment
determines the amount of gain change
for the part of the signal that exceeds the
corresponding threshold point. Find the
ALC board on the tray level control
locations drawing (1265-5305) to locate
the adjustments for the three linearity
corrector stages. Because the stages are
cascaded, the order of correction is
important. The first stage should cut-in
near white level, with the cut-in point of
the next stage toward black, and the last
stage primarily stretching sync.
Note: If additional sync stretch is
required, adjust R43 on the (A5)
sync tip clamp/modulator board.
4.1.5 IF Phase Corrector Adjustment
As shipped, the exciter was preset to
include linearity (gain vs. level) and
incidental phase (carrier phase vs. level)
predistortion. The predistortion was
adjusted to approximately compensate
the corresponding non-linear distortions
of the amplifier trays.
To adjust the linearity correctors, check
that the IF phase corrector jumper W2 on
J9 of the IF phase corrector board is
disabled. Also check that the jumper W1
on J4 of the ALC board is enabled. Select
a 3.58 MHz modulated staircase or ramp
input test video signal and monitor the
differential gain at the output of the
transmitter.
Locate (A9) the IF phase corrector board
(1227-1250). The amplitude correction
portion of the board is not utilized in this
configuration; as a result, the jumper W3
on J10 should be in the disable position
and R35 and R31 should be fully CCW.
R68 is the range adjustment and should
be set to the mid-point of the range. The
phase correction enable/disable jumper
W2 on J9 should be in the enable
position.
Check that the ALC is set to +0.85 VDC
on the front panel meter in the ALC
position. The ALC will maintain the
corresponding peak power level following
the correctors. A positive aspect of
linearity adjustment with the ALC
enabled is that the control movements
will not affect peak power.
Switch the input video test source to
select an NTSC 3.58 MHz modulated
staircase or ramp test waveform. Set up
the station demodulator and monitoring
equipment to monitor the differential
phase or intermod products of the RF
output signal. There are three corrector
stages on the IF phase corrector board,
each with a magnitude and a threshold
adjustment. They are adjusted as
necessary to correct for any differential
phase or intermod problems. Adjust the
Note: The adjustment procedure
must be repeated to achieve the
correct differential gain
predistortion.
Start with the first linearity stage and
adjust R34 CW on the IF ALC board to
420A, Rev. 0
4-3
100 Watt High Band VHF Transmitter
Chapter 4, Detailed Alignment Procedures
R3 threshold for the cut-in point of the
correction and the R7 magnitude for the
amount of the correction that is needed.
The jumper W1 on J8 is set to give the
desired polarity of the correction shaped
by the threshold R11 and magnitude R15
adjustments. After setting the polarity,
adjust the R11 threshold for the cut-in
point of the correction and the R15
magnitude for the amount of the
correction that is needed. Finally, adjust
the R19 threshold for the cut-in point of
the correction and the R23 magnitude for
the amount of the correction that is
needed.
for a 100% reading on the front panel
meter in the % Visual Output position.
With the spectrum analyzer set to zero
span mode, obtain a peak reference level
on the screen. Reconnect the jumper
cable W1 to J16 on (A5) the sync tip
clamp/modulator board. While in the
Visual Output Power position, adjust L3
for a Minimum Visual Power reading.
Turn the gain adjust pot on the front
panel until the original peak reference
level is attained. Peak L1 and C8 for
maximum aural power reading, then
adjust R20 for a 100% Aural Power
reading. Switch to the Visual Output
Power position and adjust R51 for 100%
Visual Power.
4.1.6 Calibration of the Output
Power Level
To adjust the VSWR cutback of the
transmitter, after the visual and aural
outputs are calibrated for 100%, adjust
the power to 20%, using the front panel
power adjust pot, with the jumper in
manual on the VHF filter/mixer board
(1064150). Reverse the forward and
reflected cables on the (A31) output
coupler board and adjust R39 on the
visual/aural metering board for a 20%
reading. Adjust R22 on the transmitter
control board (1068933) until the front
panel VSWR LED is illuminated. Put the
cables back in the original configuration
and place the transmitter in Standby.
Note: Do not perform this procedure
unless the power calibration is
suspect.
Switch the transmitter to standby. Move
jumper W1 on J5 of the filter/amplifier
board, high output (1064150), to the
Manual position (J5-1, 2). Preset R51,
the aural null pot on the visual/aural
metering board (1265-1309), full CCW.
Adjust R48, the offset null pot on the
visual/aural metering board (12651309), for 0% visual output.
Perform the following adjustments, with
no aural present, by removing the
jumper cable W1, the aural IF loopthrough connected to J16 on (A5) the
sync tip clamp/modulator board. Switch
the transmitter to Operate. Connect a
sync and black test signal to the video
input jack of the tray. Set up the
transmitter for the appropriate average
output power level on a wattmeter (sync
+ black and 0 IRE setup,
wattmeter=59.5 watts; sync + black and
7.5 IRE setup, wattmeter=54.5 watts).
Return jumper W1 on the filter/amplifier
board, high output (1064150), to the
AGC position (J5-2, 3). Use the front
panel gain adjust pot to set all of the
voltages to .85V. If necessary, use R73
on the transmitter control board to bring
the tray to 100% power.
This completes the detailed alignment
procedures for the transmitter. If a
problem occurred during the alignment,
refer to the board-level alignment
procedures that follow for more detailed
information.
Note: The transmitter output must
have 40 IRE units of sync.
Adjust R28, visual calibration adjust on
(A19) the visual/aural metering board,
420A, Rev. 0
4-4
100 Watt High Band VHF Transmitter
Chapter 4, Detailed Alignment Procedures
4.2 Board Level Alignment
Procedures
4.2.2 Delay Equalizer Board (12271204)
4.2.1 (Optional) 4.5 MHz Composite
Input Kit
The jumper W1 on J5 of the sync tip
clamp/modulator board, if present, must
be in the Enable position between pins 2
and 3.
If the (optional) 4.5 MHz composite input
kit is purchased, the tray is capable of
operating by using either the 4.5 MHz
composite input or the baseband audio
and video inputs. The kit adds the (A24)
composite 4.5 MHz filter board (12271244) and the (A25) 4.5 MHz bandpass
filter board (1265-1307). When the 4.5
MHz intercarrier signal generated by the
4.5 MHz composite input has been
selected by the 4.5 MHz composite input
kit, the 4.5 MHz generated by the aural
IF synthesizer board is not used. When
the 4.5 MHz intercarrier signal generated
by the baseband video and audio inputs
with baseband has been selected by the
4.5 MHz composite input kit, the
composite 4.5 MHz filter board and the
4.5 MHz bandpass filter board are not
used.
Note: This board has been factory
tuned and should not be retuned
without the proper equipment.
To tune this board:
1.
Connect a sinX/X test signal into
jack J1-2 on the delay equalizer board.
The tray has been factory tuned and
should need no alignments to achieve
normal operation. To align the tray for
the 4.5 MHz composite input, apply the
4.5 MHz composite input, with the test
signals used as needed, to the video
input jack (J1 or J2 [loop-through
connections]) on the rear of the tray.
Select the 4.5 MHz composite input by
removing the baseband select from J18-6
and J18-7 on the rear of the tray.
Monitor the video output of the
board, at the video sample jack J2,
with a video measuring set, such as
the VM700, adjusted to measure
group delay.
3.
Tune the four stages of the board
using the variable inductors (L1-L4)
and potentiometers (R7, R12, R17,
and R22) until the signal attains the
FCC group delay curve. The stages
are arranged in order of increasing
frequency. Adjust R29 as needed to
attain the same level out of the
board as into the board.
4.2.3 (A24) Composite 4.5 MHz Filter
Board (1227-1244)
This board is part of the 4.5 MHz input kit
and will only function properly with a 4.5
MHz composite input signal and the 4.5
MHz composite input selected. To align
this board:
To align the exciter using baseband video
and audio inputs, apply the baseband
video, with the test signals used as
needed, to the video input jack (J1 or J2
[loop-through connections]) and the
baseband audio to the proper baseband
audio input on the rear of the tray. For
balanced audio input, connect TB1-1(+),
TB1-2(-), and TB1-3 (GND). For
composite/stereo audio, connect the
composite audio input jack (J3 or J13
[loop-through connections]) and connect
a baseband select from J18-6 and J18-7
on the rear of the tray.
420A, Rev. 0
2.
4-5
1.
Connect the test signal from an
envelope delay measurement set to
the video input of the tray at J1 or
J2.
2.
Connect an oscilloscope to jack J7,
video out, between J7 center pin
and pin 1 or 3 ground. Adjust C21,
frequency response, if needed for
the best frequency response.
Adjust R32, video gain, for a signal
100 Watt High Band VHF Transmitter
Chapter 4, Detailed Alignment Procedures
level of 1 Vpk-pk on the
oscilloscope.
1.
Determine if jumper W4 on jack J3
is present. Jumper W4 terminates
the video input into 75Ω. Remove
jumper W4 if a video loop-through
is required on the rear chassis at
jacks J1 and J2.
2.
Set the controls R20, the white clip,
R24, the sync clip, and R45, the
sync stretch cut-in, to their full
counter clockwise (CCW) position.
Set R48, the sync magnitude, fully
CW and place the jumper W7 on
jack J4 to the clamp off, disable,
position.
3.
Connect a 5-step staircase video
test signal to the input of the
transmitter.
4.
Monitor TP2 with an oscilloscope.
Adjust R12, the video gain pot, for
1 Vpk-pk.
5.
Change the video input test signal
to a multiburst test pattern. While
monitoring TP2, adjust C8 and R32
for a flat frequency response.
Change the input video test signal
back to the 5-step staircase.
6.
Monitor TP2 with an oscilloscope.
Adjust the pot R41, manual offset,
for a blanking level of -0.8 VDC.
The waveform shown in Figure 4-1
should be observed. Move the
jumper W2 on J4 to the clamp
enable position. Adjust the pot
R152, depth of modulation, for a
blanking level of -0.8 VDC.
The output at J6 and J7 on the board
should be video only, without the 4.5
MHz aural subcarrier.
4.2.4 (Optional) (A25) 4.5 MHz
Bandpass Filter Board (1265-1307)
This board is part of the 4.5 MHz input kit
and will only function properly with a 4.5
MHz composite input signal and the 4.5
MHz composite input selected. To align
this board:
1.
Adjust the filter with L2, C3, L4,
and C7 for a frequency response of
no greater than ±0.3 dB from 4.4
to 4.6 MHz.
2.
Adjust C19 for an overall peak-topeak variation of less than ±0.3 dB
from 4.4 MHz to 4.6 MHz.
3.
Recheck the frequency response; it
may have changed with the
adjustment of the envelope delay.
If necessary, retune the board.
4.2.5 (A7) IF Carrier Oven Oscillator
Board (1191-1404)
To align this board:
1.
While monitoring J3 with a
spectrum analyzer, observe the
45.75 MHz visual IF (typical +5
dBm).
2.
Connect a frequency counter to J3
and adjust C17 for 45.750000 MHz.
3.
Note: This waveform represents the
theoretical level for proper
modulation depth. Step 9 below
describes how to set the modulation
depth through the use of a television
demodulator or a zero-spanned
spectrum analyzer tuned to the
visual IF frequency.
Connect a frequency counter to J1
and check for 50 kHz, which is the
aural phase lock loop reference.
4.2.6 (A5) Sync Tip
Clamp/Modulator Board (12651302)
To align this board:
420A, Rev. 0
4-6
100 Watt High Band VHF Transmitter
Chapter 4, Detailed Alignment Procedures
Figure 4-1. Waveform
7.
The following test setup is for the
adjustment of the depth of
modulation and ICPM at IF:
A.
B.
C.
Remove the cable that is on
J18 and connect the double
sideband 45.75 MHz visual IF
signal from J18 to a 10 dB
splitter/coupler. Connect the
coupled port of the
splitter/coupler to the RF input
of a television demodulator.
Connect the direct port to a
spectrum analyzer.
Connect the 75Ω video output
of the demodulator to the video
input of a waveform monitor.
For ICPM measurements, also
connect the quadrature output
of the demodulator to the
horizontal input of the
waveform monitor using a 250
kHz low pass filter. (An
oscilloscope can be used in
place of a waveform
monitor).
8.
Move the jumper W7 on J4 to the
clamp disable position. Readjust the
pot R41, manual offset, for the
correct depth of modulation by
observing the demodulated
waveform on the waveform monitor
or on the spectrum analyzer set to
zero span.
9.
Check the demodulated video for
proper sync to video ratio (sync is
28.6% of the total white video
signal). If sync stretch is needed,
adjust R45, sync stretch cut-in,
until sync stretch occurs. Adjust
R48, sync stretch magnitude, for
the proper amount of stretch.
Readjust R41, manual offset, if
needed, for the correct depth of
modulation.
10.
Move the jumper W7 on J4 to the
clamp enable position. Readjust the
pot R152, depth of modulation, for
the correct depth of modulation.
11.
Set the waveform monitor to
display ICPM. Preset R53 full CCW,
adjust C78 for the greatest effect at
white on the ICPM display, and then
adjust R53 for minimum ICPM.
12.
Recheck the depth of modulation
and, if necessary, adjust R152,
depth of modulation.
Set the controls of the
demodulator to the following:
Detector mode – Cont
Sound trap – In
Zero carrier – On
Auto – Sync
Audio source – Split
De-emphasis – In
420A, Rev. 0
4-7
100 Watt High Band VHF Transmitter
13.
On a spectrum analyzer, adjust the
pot R70 for a level of approximately
-10 dBm at J18.
14.
Remove the input video test signal.
Place the front panel meter in the
video position and, while monitoring
the meter, adjust pot R144, zero
adjust, for a reading of zero.
Chapter 4, Detailed Alignment Procedures
the sync clip, just below the point
where sync clipping begins to occur.
Similarly, set R20, the white clip, to
just below the point at which the
white video begins to clip.
4.2.7 (A4) Aural IF Synthesizer
Board, 4.5 MHz (1265-1303)
1.
15.
Replace the input video test
signal (the 5-step staircase).
Turn the front panel meter to
the video position and adjust
R20 on the transmitter control
board for a reading of 1V (10
on the 0-10 scale). This board
does not have sync metering.
To set up the test equipment for
this board:
A.
B.
16.
Reconnect the plug to J18 and
move the spectrum analyzer test
cable to the 41.25 IF output jack
J16. Tune C59 and L17-L20 to
maximize the 41.25 MHz aural IF
signal and minimize the out-ofband products. Adjust pot R97 for 20 dBm at J16.
17.
Reconnect the plug to J16 and
move the spectrum analyzer test
cable to the IF output jack J20.
Preset R62, the visual IF gain pot,
to the middle. Insert a multiburst
test signal into the transmitter and
observe the visual frequency
response with the spectrum
analyzer set at 1 dB/division. Tune
R63 and C30, the IF frequency
response adjustments, for a flat
frequency response (±0.5 dB).
18.
19.
While still monitoring J20 with a
spectrum analyzer, readjust R62,
visual IF gain, for a 0 dBm visual
output level. Adjust R85, A/V ratio,
for a minus 10 dB aural-to-visual
ratio or to the desired A/V ratio.
Reconnect the plug to J20.
C.
At the front of the
demodulator, connect a short
cable from the RF-out jack to
the IF-in jack.
D.
Connect a cable from the 600Ω
audio output jack of the
demodulator to the input of an
audio distortion analyzer.
2.
Set the output frequency of the
audio oscillator to 400 Hz and the
output level to +10 dBm.
3.
Center the aural carrier on the
spectrum analyzer with the
spectrum analyzer set to the
following:
Frequency/
Division – 10 kHz
Resolution
bandwidth – 3 kHz
Time/
Division – 50 msec
Using an input video test signal (the
5-step staircase) with 100 IRE
white level, monitor TP2 with an
oscilloscope. Set the control R24,
420A, Rev. 0
Connect the 600Ω balanced
audio output from an audio
oscillator to the balanced audio
input terminals of the tray at
TB1-1 (+), TB1-2 (-), and TB13 (ground) on the rear chassis.
Connect the combined IF
output at J21 (IF sample) on
the clamp modulator board to
the input of an IF splitter.
Connect one output of the
splitter to the video
demodulator and the other
output to the spectrum
analyzer.
4-8
100 Watt High Band VHF Transmitter
Chapter 4, Detailed Alignment Procedures
Trigger – Free run
4.
5.
6.
A.
Adjust L5 for approximately
+3.5 VDC at TP2.
B.
The green LED DS1 should be
illuminated, indicating a locked
condition. If not, retune L5 for
a locked condition.
75Ω stereo audio input (400 Hz at 1
Vpk-pk) to the composite audio
input jack J3 on the rear of the
tray. Follow the procedure in the
stereo generator instruction manual
for matching the level of the
generator to the exciter. Use R17 to
adjust the composite audio gain.
7.
Adjust R13, balanced audio gain, on
the aural IF synthesizer board for
±25 kHz deviation.
Check the distortion level on the
distortion analyzer (THD)=< 0.5%)
4.2.8 (A8) ALC Board (1265-1305)
(Part 1 of 2)
Check the distortion on the aural
distortion analyzer (THD=< 0.5%).
Table 4-1 describes the functions of each
LED on the ALC board (A8).
Disconnect the 600Ω balanced
audio input to the tray. Connect a
Table 4-1. ALC Board LEDs
LED
DS1 (Red LED)
DS2 (Red LED)
DS3 (Red LED)
DS4 (Red LED)
DS5 (Green LED)
1.
FUNCTION
Indicates that an abnormally low IF signal
level is present at IF input connector J1
Indicates that the ALC circuit is unable to
maintain the level requested by the ALC
reference due to excessive attenuation in
the linearity, the IF phase corrector signal
path, or the jumper W3 on J6 is in manual
gain
Indicates a video loss fault
Indicates that a Mute command is present
Indicates that the output from the
modulator is selected as the input to the
board
To align the ALC board, preset the
following controls in the tray:
B. IF Phase Corrector Board (12271250)
A. ALC Board (1265-1305)
Move W2 on J9 to phase
correction: enable. Move W3 on
J10 to amplitude correction:
disable.
Connect jumper W1 on J4 to
disable, between pins 2 and 3 (to
disable linearity correctors).
Connect jumper W3 on J6 to
manual, between pins 2 and 3 (for
manual gain control).
2.
Adjust R87, manual gain pot, to
mid-range.
420A, Rev. 0
4-9
The combined IF output of the sync
tip clamp modulator board is cabled
to jack J32 of the ALC board.
Remove J32 from the board, and
look to see if DS1, input fault, is
illuminated. Reconnect J32 and
observe that DS1 is extinguished.
100 Watt High Band VHF Transmitter
3.
Jumper W3 on J6 should be in the
manual position. Monitor jack J3
with a spectrum analyzer.
4.
With a multiburst video signal
present, tune C4 for a flat
frequency response of ±0.5 dB.
5.
Chapter 4, Detailed Alignment Procedures
remote power raise/lower kit is
present, then adjust switch S1 on
the board to maximum voltage at
TP4. Adjust R74, the range adjust,
for 1 volt at TP4.
5.
Adjust the front panel power adjust
control A20 for 0.5 VDC at TP4. If
the (optional) remote power
raise/lower kit is present, adjust
switch S1 on the board to midrange
and then adjust the front panel
power adjust control (A20) for 0.8
VDC at TP4.
6.
Disconnect the plug that is on J12
(IF output) and monitor J12 with a
spectrum analyzer. Verify an output
of approximately 0 dBm. If
necessary, adjust R99 to increase
the output level. If less output level
is needed, move the jumpers J27
and J28 to pins 2 and 3 and then
adjust R99. Reconnect J12.
7.
Move W2 on J5 to the cutback
enable position. Remove the input
video signal and verify that the
output of the transmitter drops to
25%. Adjust R71, the cutback level,
if necessary. Restore the input
video.
Before proceeding with the second
part of the ALC board alignment,
check to see that the IF phase
corrector board (1227-1250) is
functioning properly.
4.2.9 (A9) IF Phase Corrector Board
(1227-1250)
Refer to Section 4.1.5 of this chapter for
the system alignment procedures for the
IF phase corrector board. The signal level
into the board should be approximately
the same as the output of the board.
The IF input jack of the IF phase
corrector board is fed from the J3 IF O/P
jack of the ALC board (A8).
The IF output jack of the IF phase
corrector board is fed to the J7 IF I/P
jack of the ALC board (A8).
4.2.10 (A8) ALC Board, NTSC (12651305) (Part 2 of 2)
To align this board:
Note: The following step affects the
response of the entire transmitter.
1.
Input a multiburst video test signal.
Connect a spectrum analyzer to
J11. Tune C63 for a flat frequency
response of ±0.5 dB.
8.
2.
Move the Operate/Standby switch
on the front panel to the Operate
position.
3.
Place jumper W3 on jack (J6) in the
Manual mode and adjust R87 for
0.5 volts at TP4.
Connect a video sweep signal to the
input of the tray. Monitor the
output of the
system with a spectrum analyzer.
Adjust C71 with R103 and C72 with
R106 as needed to flatten the
response. C71 and C72 adjust for
the frequency of the correction
notch being applied to the visual
response of the transmitter. R103
and R106 are used to adjust the
depth and width of the correction
notch.
4.
Place jumper W3 on J6 in the Auto
mode and adjust the front panel
power adjust control A20 full
clockwise (CW). If the (optional)
9.
Refer to the Section 4.1.4 of this
chapter for the system alignment
procedures for the linearity
420A, Rev. 0
4-10
100 Watt High Band VHF Transmitter
correctors. Controls R13, R18, and
R23, the magnitude controls,
should be set full CW. Controls R34,
R37, and R40 are the linearity cutin adjustments.
4.2.11 (A14-A1) Channel Oscillator
Board (1145-1201)
This board is mounted in (A14) the
channel oscillator assembly (1145-1202).
To align the board:
1.
Connect the main output of the
channel oscillator (J1) to a
spectrum analyzer, tuned to the
crystal frequency, and peak the
tuning capacitors C6 and C18 for
maximum output. Tune L2 and L4
for maximum output. The output
level should be about +5 dBm. The
channel oscillator should maintain
an oven temperature of 50° C.
If a spectrum analyzer is not
available, connect a DVM to TP1 on
the x4 multiplier board. Tune
capacitors C6 and C18 for
maximum voltage, then also tune
L2 and L4 for maximum voltage
output at TP1.
2.
Connect the sample output of the
channel oscillator (J2) to a suitable
counter and tune C11, coarse
adjust, and C9, fine adjust, to the
crystal frequency.
Note: Do not repeak C6, C18, L2, or
L4. This may change the output
level.
Note: While adjusting C9 and C11 to
the crystal frequency, the peak
voltage monitored at TP1 of the x4
multiplier board should not
decrease. If a decrease does
occur, there may be a problem with
the crystal. Contact ADC
Telecommunications Field Support
for further instructions.
420A, Rev. 0
Chapter 4, Detailed Alignment Procedures
Note: If the VCXO board (11451204) in the VCXO assembly (11451206) is used, the C9 fine frequency
adjust is not located on the VCXO
board. Use R9 on the FSK w/EEPROM
board.
3.
Reconnect the main output (J1) of
the channel oscillator to the input
(J1) of the x4 multiplier.
4.2.12 (A15-A1) x4 Multiplier Board
(1174-1112)
While monitoring the board with a DC
voltmeter, maximize each test point
voltage by tuning the broadband
multipliers in the following sequence:
1.
Monitor TP1 with a DVM and tune
C4 for maximum voltage. Monitor
TP2 with a DVM and tune C6 and
C10 for maximum voltage.
Monitor TP3 with a DVM and tune
C12; repeak C4, C6, and C10 for
maximum voltage.
2.
Connect a spectrum analyzer,
tuned to four times the crystal
frequency, to the x4 multiplier
output jack (J2). While trying to
keep the out-of-band products to
a minimum, monitor the output
and peak the tuning capacitors for
maximum output.
The output of the x4 multiplier connects
to (A11-A1) the filter/mixer board.
4.2.13 (A11-A1) Filter/Mixer Board
(1150-1102)
To align the board:
1.
Monitor J4, the LO output of the
board, with a spectrum analyzer
and adjust C12 and C18 for
maximum output (+14 dBm) at
the LO frequency.
2.
Adjust C13 and C17 for the best
frequency response for the LO
frequency.
4-11
100 Watt High Band VHF Transmitter
Chapter 4, Detailed Alignment Procedures
4.2.14 (A11-A2) Filter/Amplifier
Board, High Output (1064150)
amps on the meter and then adjust R9
for 1.5 amps total current on the meter.
To set the bias for the final amplifier
board (A23-A4), the RF drive will need to
be removed. To monitor the current
adjustment, read the voltage drop across
the 3-watt resistor, R7, mounted on the
overcurrent protection board (12731130). Using Ohm’s Law, determine the
voltage drop across the resistor (1.5
amps x 0.01Ω=0.015 volts). Preset the
bias adjust pots R5 and R9 CCW. Slowly
adjust the bias adjust pot R5 for .75
amps on the meter and then adjust R9
for 1.5 amps total current on the meter.
The filter/amplifier board has been
factory swept and adjusted for a 6 MHz
bandwidth.
Note This board should not be tuned
without the proper equipment.
The filtered output connects to J1 of the
board and is amplified by U1 to a
nominal +11 dBm visual and +1 dBm
aural level by adjusting R9. The output is
fed to the (A23-A1) high-band amplifier
board (1218-1201) mounted on the VHF
amplifier heatsink assembly (A23).
4.2.15 (A23-A1, A23-A3, A23-A4)
High-Band Amplifier Boards (12181201)
4.2.16 Frequency Adjustment of the
High-Band Amplifier Boards
The following procedures describe how to
adjust these boards:
Each of the high-band amplifier boards
has 20 dB of gain. A23-A1 is biased at 2
amps of idling current with no RF drive
applied. A23-A3, A4 are biased at 1.5
amps each, with no RF drive applied. To
set the bias for the final amplifier board
(A23-A1), the RF drive will need to be
removed. To monitor the current
adjustment, read the voltage drop across
the 3-watt resistor, R5, mounted on the
overcurrent protection board (12731130). Using Ohm’s Law, determine the
voltage drop across the resistor (2 amps
x 0.01Ω=0.020 volts). Preset the bias
adjust pots R5 and R9 CCW. Slowly
adjust the bias adjust pot R5 for 1 amp
on the meter and then adjust R9 for 2
amps total current on the meter.
Move the ALC/manual jumper on the
(A11-A2) filter/amplifier board to the
manual position, disabling the ALC
circuit. Remove two fuses (F2 and F3) on
the overcurrent protection board to
disable the (A23-A3 and A4) high-band
amplifier boards. Connect a spectrum
analyzer to output connector J2 on the
(A23-A1) high-band amplifier board.
Adjust C9 and C19 for peak power and
frequency response.
To set the bias for the final amplifier
board (A23-A3), the RF drive will need to
be removed. To monitor the current
adjustment, read the voltage drop across
the 3-watt resistor, R6, mounted on the
overcurrent protection board (12731130). Using Ohm’s Law, determine the
voltage drop across the resistor (1.5
amps x 0.01Ω=0.015 volts). Preset the
bias adjust pots R5 and R9 CCW. Slowly
adjust the bias adjust pot R5 for .75
Move the spectrum analyzer to the
output connector J2 on the (A23-A4)
high-band amplifier board. Remove fuse
F2, install fuse F3, and adjust C9 and
C19 (on the [A23-A4] high-band
amplifier board) for peak power and
frequency response.
420A, Rev. 0
Move the spectrum analyzer to the
output connector J2 on the (A23-A3)
high-band amplifier board. Install fuse F2
and adjust C9 and C19 (on the [A23-A3]
high-band amplifier board) for peak
power and frequency response.
Move the spectrum analyzer to the
output, J2, of the (A23) amplifier
heatsink assembly. Install all of the fuses
and readjust C9 and C19, if needed, on
4-12
100 Watt High Band VHF Transmitter
Chapter 4, Detailed Alignment Procedures
all three amplifier boards for peak power
and frequency response.
4.2.19 (A3) +12 VDC (4A)/-12 VDC
(1A) Power Supply Board (12651312)
4.2.17 (A29) Overcurrent Protection
Board (1273-1130)
There are no adjustments to this board.
4.2.18 (A19) Visual/Aural Metering
Board (1265-1309)
The board is calibrated to give a peak
detected output indication to the front
panel meter for % Visual Output, %
Aural Output, and % Reflected Output
and should not be adjusted. If necessary,
refer to Section 4.1.2 of this chapter for
the alignment procedures for the front
panel meter.
There are no adjustments to this board.
DS1 will be lit if a +12 VDC output is
connected to J6. DS2 will be lit if a +12
VDC output is connected to J3. DS3 will
be lit if a +12 VDC output is connected to
J4. DS4 will be lit if a +12 VDC output is
connected to J5. DS5 will be lit if a -12
VDC output is connected to J7 and J8.
4.2.20 (A31) Output Coupler Board
(1211-1004)
There are no adjustments to this board.
This completes the detailed alignment
procedures for the boards in the 420A
transmitter.
420A, Rev. 0
4-13

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