UBS Axcera 840A User Manual

10-kW UHF Transmitter with Chapter 5, Detailed Alignment Procedures
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Chapter 5

Detaile d Alignment Procedures

This transmitter was aligned at the
factory and should not require additional
alignments to achieve normal operation.
Before beginning the alignment
procedures, check that the RF output at
J2 of (A18) the output coupler assembly
of the transmitter is terminated into a
dummy load or is co nnect ed to the
antenna. While performing a ny
alignments, refer to the Test Data Sheet
for the transmitter and compare the final
readings from the factory with the
readings on each of the trays. They
should be very similar. If a reading is off
by a substantial amount, the problem is
lik e ly t o be in th a t t ra y.

5.1 (A1-A4) UHF Exciter Tray
(1063301; Appendix A)

If the (o p tional) 4. 5-MHz com p o s ite in p u t
kit has been purchased, the UHF exciter
tray is capable of operating using either
the 4.5-MH z comp os ite input or the
baseband audio and video inputs. The kit
adds (A24) the composite 4.5-MHz filter
board and (A25) the 4.5-MHz bandpass
filter board to the UHF exciter. The 4.5
MHz generated by the aural IF
synthesizer board is not used when the

4.5-MHz composite input kit has selected
the 4.5-MHz intercarrier signal generated
by the 4.5-MHz composite input. The
composite 4.5-MHz filter board and the

4.5-MHz bandpass filter board are not
used when the 4.5-MHz composite input
kit uses the 4.5-MHz intercarrier signal
generated by the baseband video and
audio inputs with baseband select.

The exciter tray has been factory tuned
and should not need to be aligned to
achieve normal operation. To align the
UHF exciter for 4.5-MHz composite input,
apply the 4.5-MHz composite input, with
the test signals used as needed, to video
input jack J1 on the rear of the tray.
Select the 4.5-MHz composite input by
removing the baseband select from J7-6

and J7- 7 on the rea r of the tray, if
applied.

To align the UHF exciter using baseband
video and audio inputs, connect the
baseband video, with the test signals
used as needed, to video input jack J2 on
the remote interface panel. For balanced
audio input, connect the baseband audio
to TB1-1(+), TB1-2(-), and TB1-3 (GND)
on the remote inte rface panel. Fo r
composite/stereo audio, connect the
stereo source to J6 on the remote
interface panel.

5.1.1 (A6) (Optional) Delay Equalizer
Board (1227-1204; Appendix B)

This board has been factory tuned and
should not be retuned without the proper
equipme nt. If it is neces sar y to tune the
board:

1. Select a sinX/X test signal as the
video source to the delay equalizer
board.

2. Monitor the video output of the
board at video sample jack J2 with
a video meas uring set (VM700) that
has been adjusted to meas ure
group delay.

3. Tune the four stages of the board
using the variable inductors (L1-L4)
and potentiometers (R7, R12, R17,
and R22) unti l the signa l attai ns the
FCC group delay curve. The stages
are arranged in order of increasing
frequency. Adjust R29 as needed to
attain the same level coming out of
the board as is going into the
board.

840A, Rev. 0 5-1

10-kW UHF Transmitter with Chapter 5, Detailed Alignment Procedures
Feedforward Drive

5.1.2 (A24) (Optional) Composite

4.5-MHz Filter Board (1227-1244;
Appendix B)

The (A24 ) (optional) composite 4.5-MHz
filter board will only function properly
with a 4.5-MHz composite input signal
and with the 4.5-MHz composite input
selected.

Connect the test signal from an envelope
delay measurement set to the video
input of the tray at J1 or J2.

Connect an oscilloscope to jack J7, video
out, between the J7 center pin and pin 1
or 3 ground. Adjust C 21, frequency
response, if needed, for the best
frequency response. Adjust R32, v ideo
gain, for a signal level of 1 Vpk-pk on the
oscilloscope.

The output at J6 and J7 of the board
should be video only with no 4.5-MHz
aural subcarrier.

5.1.4 (A7) IF Carrier Oscillator Board

(1191-1404; Appendix B)

To align (A7) the IF carrier oscillator
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. Connect a frequency counter to J1
and check for 50 kHz; th is is the
aur al p h as e lo c k lo op (P LL)
reference.

5.1.5 (A5) Sync Tip Clamp/

Modul ator Board (1265-1302;
Appendix B)

To align (A5) the sync tip clamp/
modulator board:

5.1.3 (A25) (Optional) 4.5-MHz
Bandpass Filter Board (1265-1307;
Appendix B)

The (A25) (optional) 4.5-MHz bandpass
filter board will only function properly
with a 4.5-MHz composite input signal
and with the 4.5-MHz composite input
selected.

Adjust the filter with L2, C3, L4, and C7
for a frequency resp onse of no greater
than ±.3 dB from 4.4 to 4.6 MHz.

Adjust C19 for an overall peak-to-peak
variation of less t han ±.3 dB from 4.4
MHz to 4.6 MHz.

Recheck the frequency response; it may
have changed with the adjustment of the
envelope delay. If necessary, retune the
board.

1. Determine if jumper W4 on jack J3
is present. Jumper W4 terminates

the video input into 75Ω. Remove
jumper W4 if the video loop­through is required on the rear
chassis at jacks J1 and J2.

2. Se t the controls R20, the white clip,
R24, the sync clip, and R45, the
sync stretch cut-in, to their fully
counter-clockwise (CCW) position.
Set R48, the sync magnitude, fully
clockwise (CW).

3. Place the jumper W7 on jack J4 to
the clamp off, disable, position.

4. Connect a 5-step staircase video
test signal to the input of the
transmitter.

5. Monitor TP2 with an oscilloscope.
Adjust R12, the video gain pot, for
1 Vpk-pk.

840A, Rev. 0 5-2

6. Change the video input test signal
to a multib urst test pattern. While

10-kW UHF Transmitter with Chapter 5, Detailed Alignment Procedures

0 Volt

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monitoring TP2, adjust C8 and R32
for a flat-f req u e nc y res p onse.
Change the input video test signal
back to the 5-step staircase.

7. Monitor TP2 with an oscilloscope.
Adjust the pot R41, manual offset,

Figure 5-1. Waveform at TP2.

Note: The waveform in Figure 5-1
repres ent s the theoretical level for
proper modulation depth. Step 9
below describes how to set the
modulation d epth through the use of
a television demodulator or a zero­spanned sp ectrum analyzer t uned to
the vis ual IF frequenc y .

8. The following test setup is for the
adjustment of the depth of
modulation and ICPM at IF:

A. Remove the cable that is now

on J18. 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 inp ut of a
television demodulator.
Connect the direct port to a
spectrum analyzer.

B. Connect the 75-Ω video output

of the demodulator to the video
input of a waveform monitor.
For incidental carrier phase
modulation (ICPM)

for a blanking level of -0.8 VDC.
The waveform in Figure 5-1 should
be observed at this point. Move
jumper W2 on J4 to the clamp
enable position. Adjust pot R152,
depth of modulation, for a blanking
level of -0.8 VDC.

s

.1 Volts

measurements, also connect
the q uadrature 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
pla ce of a waveform monitor).

C. Set the controls of the

demodulator as follows:

• Detector Mode: Cont

• Sound Trap: In

• Zero Carrier: On

• Auto: Sync

• Audio Source: Split

• De-Emphasis: In

9. Move jumper W7 on J4 to the clamp
disable position. Readjust pot R41,
manual off set, for the correct depth
of modulation by observing the
demodulated waveform on the
waveform monitor or on the
spectrum analyzer set to zero span.

10. Check the demodulated video for
the proper sync-to-video ratio (sync
is 28.6% of the total white video

840A, Rev. 0 5-3

10-kW UHF Transmitter with Chapter 5, Detailed Alignment Procedures
Feedforward Drive

signal). If sync stretch is needed,
adjust R45, sync stretch cut-in,
until sync stretch occurs. Adjust
R48, sync stretc h magnitude, for
the proper amount of stretch.
Readjust R41, manual offset, if
necessary, for the correct depth of
modulation.

11. Move jumper W7 on J4 to the clamp
enable position. Readjust pot R152,
the depth of modulation, for the
correct depth of modulation.

12. Set the wavefo rm monitor to
display ICPM. Preset R53 fully CCW,
adjust C78 for the greatest effect at
white on the ICPM display, and
adjust R53 for minimum ICPM.

13. Recheck the depth of modulation
and, if necessary, adjust R152,
depth of modulation.

14. Adjust pot R70 for a level of
approximately -10 dBm on the
spectrum analyzer at J18.

15. Remove the video input. Place the
front panel meter in the video
pos ition and, while monitoring the
meter, adjust pot R144, zero
adjust, for a reading of zero.

16. Replace the video inp ut 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 100 (10
on the 0-to-10 scale). This
board does not have sync
metering.

17. Reconnect the plug to J18 and
move the spectrum analyzer test
cable to 41.25 IF output jack J16.
Tune C59 and L17-L20 to maximize
the 41.25-MHz aural IF signal and
minimize the out-of-band products.
Adjust pot R97 for -20 dBm at J16.

18. Reconnect the plug to J16 and
move the spectrum analyzer test
cable to 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 C 30, th e IF freq ue nc y
response adjustments, for a flat­frequency response (±0.5 dB).

19. While still monitoring J20 with a
spectrum analyzer, readjust R62,
visual IF gain, for a visual output
level of 0 dBm. Adjust R85, A/V
ratio, for a -10 dB aural-to-visual
ratio or to the needed A/V ratio.
Reconnect the plug to J20.

20.

Using an input video test signal (the

5-step staircase) with a 100 IRE
white level, monitor TP2 with an
oscilloscope. Set the control R24,
the sync clip, just below the point
where sync clipping begins to occur.
Also, set R20, the white clip, to the
point just below where the white
video begins to clip.

Note: This procedure should be
performed after the system setup or
if linearity problems occur.

5.1.6 (A26) Diacrode VSBF Bypass

Board (1293-1230; Appendix B)

The (A26) diacrode VSBF bypass board is
used to bypass the clamp board saw filter
when S1 and S2 are in the enable
position. This double sideband signal can
be used to sweep the tube cavity with a
double sideband and no aural present. C2
is us ed to flatten the double sideband
response. S1 and S2 are normally in the
bypass position.

840A, Rev. 0 5-4

10-kW UHF Transmitter with Chapter 5, Detailed Alignment Procedures
Feedforward Drive

5.1.7 (A4) Aural IF Synthesizer
Board, 4.5 MHz (1265-1303,
Appendix B)

1. The test equipment setup f or (A4)
the aural IF synthesizer board, 4.5
MHz, is as follows:

A. Connect a 600-Ω balanced

audio output from an audio
oscillator to the balanced audio
input te rminals of the tray at
TB1-1 (+), TB1-2 (-), a nd TB1­3 (ground) on the rear chassis.

B. Connect the combined IF

output at J21, the IF sample on
the clamp modulator board, to
the input of a n IF splitter.
Connect one output of the
split ter to the video
demodulator and the other
output to the spectrum
analyze r.

C. Connect a short cable at the

front of the demodulator from
the RF-out jack to the IF-in
jack.

D. Connect a cable from the 600-

Ω 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

• Trig g e r: Fr ee run

B. The green LED DS1 should be

illuminated, indicating a locked
condition. If not, retune L5 for
a locked condition.

4. Adjust R13, balanced audio gain, on
the aural IF synthesizer board for
±25 kHz deviation.

5. Check the distortion on the aural
distortion analyzer (< 0.5%).

6. Disconne ct t he 600-Ω balanced
audio input to the tra y. Conn ect a
75-Ω stereo audio input (400 Hz at
1 Vpk-pk) to 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. R17 is used to adjust
the composite audio gain.

7. Check the distortion level on the
distortion analyzer (< 0.5%).

5.1.8 (A8) ALC Board (1265-1305;

Appendix B) (Part 1 of 2)

The following details the meaning of each
LED of (A8) the ALC board when it is
illuminated:

• DS1 - Red LED: Indicates that an

ab norm ally lo w IF sign a l le v e l is
present at IF input connector J1

• DS2 - Red LED: Indicates that the

ALC circuit is unable to maintain the
signal level requested by the ALC
reference; this is usually due to
excessive attenuation in the linearity
or the IF phase corrector signal path,
or becaus e the jumper W3 on J6 is in
manual gain

• DS3 - Red LED: Indicates a video loss

fault

A. Adjust L5 for approximately

+3.5 VDC at TP2.

840A, Rev. 0 5-5

• DS4 - Red LED: Indicates that a Mute

command is present (not used in this
configuration)

10-kW UHF Transmitter with Chapter 5, Detailed Alignment Procedures
Feedforward Drive

• DS5 - Green LED: Indicates that the
outpu t from the modulator is selected
as the input to the ALC board

1. To align the ALC board, preset the

following controls in the UHF exciter
tray:

• ALC board – Move jumper W1 on J4
to disable, between pins 2 and 3 (to
disable linearity correctors); move
jumper W3 on J6 to manual, between
pins 2 and 3 (for manual gain
control); adjust R87, the manual gain
pot, to mid-rang e

• IF phase corrector board – Move
jumper W2 on J9 to the phase
correction enable position; move the
jumper W3 on J10 to the amplitude
correction disable position.

2. 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
check to see that DS1, Input Fault,
is illuminated. Reconnect J32 and
check to see that DS1 is
extinguished.

3. Jumper W3 on J6 should be in the

manual position; monit or jack J3
with a spectrum analyzer.

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 J3, the IF
output jack of (A8) the ALC board.

The IF output jack of the IF phase
corrector board is fed to J7, the IF input
jack of (A8) the ALC board.

5.1.10 (A8) ALC Board, NTSC (1265­1305; Appendix B) (Part 2 of 2)

Input a multiburst video test signal at the
baseband video input. Connect a
spectrum analyzer to J11. Tune C63 for a
flat-frequency response of ±0.5 dB.

Move the Operate/Standby switch on the
front panel of the transmitter to the
Operate posi tion.

Place jumper W3 on jack J6 in the
Manual mode and adjust R87 for 0.8
volts at TP 4.

Place jumper W3 on J6 in the Auto mode
and adjust the front panel power adjust
control A20 fully CW. If the optional
rem ote power raise/lower kit is present,
adjust switch S1 on the board to
maximum voltage at TP4. Adjust R74,
the range adjust, for 1 volt at TP4.

4. With a multiburst video signal

present, tune C4 for a flat­frequency resp onse of ±0.5 dB.

5. Before proceeding with part 2 of the

ALC board alignment (described in
section 5.1.10), check the IF phase
corrector board to make sure that it
is functioning properly.

5.1.9 (A9) IF Phase Corrector Board

(1227-1250; Appendix B)

Refer to the system alignme nt
procedures at the end of this chapter for
the set up of (A9) the IF phase corrector
board in the exciter tray. The signal level

840A, Rev. 0 5-6

Adjust the front panel power adjust
cont rol (A20) for 0.8 VDC at TP4. If the
optional remote power raise/lower kit is
present, adjust switch S1 on the board to
the mid-range of its travel and then
adjust the front panel Power Adjust
cont rol (A20) for 0.8 VDC at TP4.

Dis connect the plug that is now on J12
(IF ou tput) and monitor the output with a
spectrum analyzer. The output should be
approximately 0 dBm. Adjust R99, if
necessary, to increase the output level. If
a smaller o utput level is needed, move
the jumpers J27 and J28 to pins 2 and 3
and adjust R99 as needed. Reconnect
J12.

10-kW UHF Transmitter with Chapter 5, Detailed Alignment Procedures
Feedforward Drive

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 video input signal.

Note: This step affects the response
of the entire transmitter. Connect a
video sweep signal to the input of
the tray. Monitor the output of the
system with a spectrum analyzer.
Adjus t C71 with R103 and C72 with
R106, as needed, to flatten the
response. C71 and C72 can b e
adjusted for the frequency of the
correction notch being applied to the
visual response of the tran smitte r.
R103 and R106 are used to adjust
the depth and width of the correction
notch.

Controls R13, R18, and R23, the
magnitude controls, should be set fully
CW. Controls R34, R37, and R40 are the
linearity cut-in adjustments.

5.1.11 (A11) UHF Upconverter Board

(1265-1310; Appendix B)

To alig n (A11) the UHF upconverter
board, place W1 on J10 in the Manual
position. R10 is a gain control that is
adjusted to give an output of
approximately +17 dBm at J5 of the
board with an input of 0 dBm of IF.

5.1.12 (A14-A1) Channel Oscillato r

Board (1145-1201; Appendix B)

The (A14 -A1) channel oscillator board is
mounted in (A14) the channel oscillator
assembly. To align this board:

1. Connect J1, the main output of the

channe l oscillator, to a spectrum
analyzer tuned to the crystal
frequency. 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 sp ectrum analyzer is not
available, connect a digital
voltmeter (DVM) to TP1 on the x8
multiplier board. Tune capacitors C6
and C18 for maximum voltage and
tune L2 and L4 for maximum
voltage output at TP1.

2. Connect J2, the sample output of
the channel oscillator, to a suit able
counter and tune C11, coarse
adjust, to the crystal frequency.
Tune C9 for the fine-frequency
adjustment.

Caution: Do not repeak C6, C18, L2,
or L4. This can change the output
level.

Note: While adjusting C9 an d C11 to
the crystal frequency, the peak
vol t age monitored at TP1 of the x8
multiplier board should not decrease.
If a decr ease does oc cur, there may
be a problem with the crystal.
Contact the ADC Field Service
Department for further instructio ns.

Note: If the channel oscillator in the
channel oscillator assembly is used,
the C9 fine-frequency adjust is not
on the channel oscillator board. It
can be found on the FSK
w/EEPROM board by using R9.

3. Reconnect J1, the main output of

the channel oscillator, to J1, the
input of the x8 multiplier.

5.1.13 (A15-A 1) x8 Multiplier Board

(1227-1002; Appendix B)

The (A15 -A1) x8 multiplier board is
mounted in an x8 multiplier enclosure
assembly. During no rmal operation, the
green LED DS1, which can be seen
through the access hole in the enclosure
assembly, will be lit to indicate that the
LO is present at the output of the x8
multiplier boa r d.

840A, Rev. 0 5-7

10-kW UHF Transmitter with Chapter 5, Detailed Alignment Procedures
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Connect a spectrum analyzer to
output jack J2 of the board.

Tune C4, C6, C10, C12, C18, and C20 for
maximum output.

Readjust all of the capacitors to minimize
the seventh and the ninth harmonics of
the channel oscillator frequency. They
should be at least -30 dB down without
affecting the x8 multiplier output.

If a spectrum analyzer is not available, a
DC voltmeter can be used. When a
voltmeter is used, the harmonic
frequencies must be minimized to
prevent interference with other channels.

While monitoring each test point with a
DC voltmeter, maximize each test point
by tuning the broadband multipliers in
the following sequence:

• Monitor TP1 with a DVM and tune C4
for maximum (typical 0.6 VDC).

• Monitor TP2 and tune C6 and C10 for
maximum (typical 1.2 VDC).

• Monitor TP3 and tune C12 and C18
for maximum (typical 2.0 VDC).

• Monitor TP4 and tune C20 for
maximum.

• Repeak C12 and C10 while
monitoring TP4 (typical 3.5 VDC).

• The typical output level is +15 dBm.

5.1.14 (A19) Visual/Aural Metering

Board (1265-1309; Appendix B)

5.1.15 (A3) +12 VDC (4A)/-12 VDC
(1A) Power Supply Board (1265­1312; Appendix B)

There are no adjustments that need to
be made to (A3) the +12 VDC (4A)/-12
VDC (1A) power supply board. DS1 will
be lit if a +12 VDC output is c onnected 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 c onnected to
J5. DS5 will be lit if a -12 VDC output is
connected to J7 and J8.

5.1.16 Transmitter Control Board
(1293-1221; Appendix B)

To align the VSWR cutback, adjust the 3­watt amplifier tray for a 12.5% Visual
Power reading on the metering control
panel. Reverse the J6 and J3 cables on
(A2-A2) the coupler on the output of the
diacrode cavity. Adjust R22 unto the
VSWR light sta rts to ill umi nate on the
exciter front panel. Place the J3 and J6
cables back in their original positions.

To align the video metering, insert a
composite or some other 100-IRE test
signal into the exciter tray. Adjust R20
for a full-scale reading (1 volt) on the
bottom scale of the front panel meter of
the exciter tray in the video metering
position.

To align the audio meter ing, adjust the
audio input level for a ±25 kHz deviation
using a spectrum analyzer. Adjust R19 on
the board for a 25-kHz reading on the
bottom scale of the front panel meter of
the excite r tray.

The (A19) visual/aural metering board is
adjusted to give a peak-detected output
indication to the front panel meter for the
visual output and aural output of the
driver cabinet. The board should not
need to be adjusted to achieve normal
operation.

840A, Rev. 0 5-8

This completes the detailed alignment
procedures for the UHF exciter tray.

10-kW UHF Transmitter with Chapter 5, Detailed Alignment Procedures
Feedforward Drive

5.2 (A9) 3-Watt Amplifier Tray

(1068203; Appendix A)

The 3-watt amplif ier tray has been
aligned at the factory and should not
require any further adjustments. If an
alignment is nece ssary, terminate the 3 ­watt tray into a dummy load before
performing any adjustments.

5.2.1 (A1) UHF Filter (1007-1101;

Appendix B)

The (A1) UHF filter (1007-1101) has
been factory swept and should not be
tuned without the proper equipment. The
filtered output is sent to (A2) the AGC
board input jack J1.

5.2.2 (A2) AGC Board (1007-1201;

Appendix B)

Perform the following steps to align (A2)
the AGC board (1007-1201):

1. With S1 on the AGC board in the
Manual position, adjust R32 for about
a -2 dBm output at J2.

2. The RF output of the AGC board is fed
to (A27) the UHF phase shifter board
input jack J1.

5.2.4 (A3) UHF Amplifier/Regulato r
Board (1007-1204; Appendix B)

The (A3) UHF amplifier/regulator board
(10 07- 12 04) ha s no tun i ng ad just ments
and has a gain of about +17 dB. The
outpu t is fed to (A5) the 3-watt amplifi er
board #1 input jack J1.

5.2.5 (A5) 3-Watt Amplifier # 1
(1007-1211; Appendix B)

The (A5) 3-watt amplifier #1 (1007-

1211) has a gain of about 9 dB and is
tuned with C2, C4, and C8 for maximum
output.

The operating current, static current with
no drive applied, of the amplifier is set to
800 milliamps with R7 on (A6) the opto­bias board. The current is determined by
measuring the voltage drop across R3,
the 3.3-ohm resistor in the collector
circuit of Q1 on the amplifier board, and
adjusting R7 for a voltage drop of 2.64
volts.

The RF output is fed to (A7) the 3-watt
amplifier board #2.

5.2.6 (A7) 3-Watt Amplifier # 2
(1007-1211; Appendix B)

5.2.3 (A27) UHF Phase Shifter Board

(1142-1315; Appendix B)

The (A27) UHF phase shifter board
(1142-1315) adjusts the phase of the
signal to produce the maximum output of
the transmitter when the two parallel
amplifiers are added together.

Adjust R7 on the front panel of the tray
for maximum output power. Monitor the
com bined % Output power on the front
panel meter of the transmitter.

The phase-corrected RF output is fed to
(A3) the UHF amplifier/regulator board
input jack J1.

840A, Rev. 0 5-9

The (A7) 3-watt amplifier #2 (1007-

1211) has a gain of about 9 dB and is
tuned with C2, C4, and C8 for maximum
output.

The op erating current of the amplif ier is
set to 850 mA with R7 on (A 8) the opto­bias board. The current is determined by
measuring the voltage drop across R3,
the 3.3-ohm resistor in the collector
circuit of Q1 on the amplifier board, and
adjusting R7 for a voltage drop of 2.8
volts.

The output of the amplifier is fed through
(A9) the UHF dual coupler assembly to
RF output jack J2 of the tray. A forward
and reflected power sample is taken from
the UHF dual coupler assembly and fed to
(A10) the dual peak detector board.