M/A-Com 19D902797G3 User manual

Maintenance Manual
LBI-38674L
450-470 MHz, 110 WATT POWER AMPLIFIER 19D902797G3
403-425 MHz, 90 WATT POWER AMPLIFIER 19D902797G6
425-450 MHz, 90 WATT POWER AMPLIFIER 19D902797G7
380-400 MHz, 75 WATT POWER AMPLIFIER 19D902797G8
470-494 MHz, 90 WATT POWER AMPLIFIER 19D902797G9
492-512 MHz, 90 WATT POWER AMPLIFIER 19D902797G10
410-430 MHz, 90 WATT POWER AMPLIFIER 19D902797G11
TABLE OF CONTENTS
Section Page
1.0 SPECIFICATIONS................................................................................................................................................... 3
2.0 DESCRIPTION ........................................................................................................................................................4
3.0 CIRCUIT ANALYSIS..............................................................................................................................................5
3.1 POWER AMPLIFIER ..........................................................................................................................................5
3.1.1 Exciter (U7) ..................................................................................................................................................5
3.1.2 Small Signal Gain Stage ...............................................................................................................................5
3.1.3 Low Level Amplifier (U1)............................................................................................................................5
3.1.4 Driver (Q1) ................................................................................................................................................... 5
3.1.5 Power Amplifier Finals (Q2 & Q3) ..............................................................................................................6
3.1.6 Low Pass Filter ............................................................................................................................................. 6
3.2 POWER CONTROL ............................................................................................................................................7
3.2.1 Keying and Unkeying the PA .......................................................................................................................7
3.2.2 PA Output Power Set....................................................................................................................................7
3.2.3 PA Protection................................................................................................................................................ 7
3.2.4 Theory of Operation......................................................................................................................................7
3.2.5 Signal Interface.............................................................................................................................................8
4.0 TROUBLESHOOTING .........................................................................................................................................10
4.1 TROUBLESHOOTING GUIDE ........................................................................................................................ 10
4.2 LOW PASS FILTER TEST PROCEDURE .......................................................................................................13
4.2.1 Recommemded Test Equipment .................................................................................................................13
4.2.2 Test Set-Up and Procedure .........................................................................................................................13
5.0 PARTS LIST .......................................................................................................................................................... 14
6.0 PRODUCTION CHANGES...................................................................................................................................23
7.0 IC DATA ................................................................................................................................................................26
8.0 ASSEMBLY DIAGRAMS..................................................................................................................................... 29
8.1 POWER AMPLIFIER 19D902797G3 & G6 THROUGH G11..........................................................................29
8.2 COVER ASSEMBLY 19B801659G3 ................................................................................................................30
9.0 ASSEMBLY, OUTLINE & SCHEMATIC DIAGRAMS FOR LOW PASS FILTER MODULE 19D902856G331
10.0 OUTLINE DIAGRAM...........................................................................................................................................32
10.1 POWER AMPLIFIER BOARD A1 19D902856G3, G6, G7, G8, G9, G10 & G11........................................... 32
11.0 SCHEMATIC DIAGRAM .....................................................................................................................................33
11.1 POWER AMPLIFIER ASSEMBLY 19D902 797G3 & G6 THROUGH G11 .................................................. 33
12.0 OUTLINE & SCHEMATIC DIAGRAM FOR 470-512 MHz LOW PASS FILTER MODULE 19D902856G9 .34

NOTE
Repairs to this equipment should be made only by an authorized service technician or facility designated by the
supplier. Any repairs, alterations or substitution of recommended parts made by the user to this equipment not
approved by the manufacture could void the user’s authority to operate the equipment in addition to the
manufacture’s warranty.
This manual is published by M/A-COM, Inc., without any warranty. Improvements and changes to this manual necessitated by typographical
errors, inaccuracies of current information, or improvements to programs and/or equipment, may be made by M/A-COM, Inc., at any time
and without notice. Such changes will be incorportated into new editions of this manual. No part of this manual may be reproduced or
transmitted in any form or by any means, electronic or mechanical, including photocopying and recording, for any purpose, without the
express written permission of M/A-COM, Inc.
Copyright© 1992 - 2003 M/A-COM, Inc. All rights reserved.
2 LBI-38674L

SPECIFICATIONS
1.0 SPECIFICATIONS1
ITEM SPECIFICATION
FREQUENCY 450 MHz - 470 MHz (G3)
403 MHz - 425 MHz (G6)
425 MHz - 450 MHz (G7)
380 MHz - 400 MHz (G8)
470 MHz - 494 MHz (G9)
492 MHz - 512 MHz (G10)
410 MHz - 430 MHz (G11)
OUTPUT POWER (RF) 65 watts - 130 watts (G3)
55 watts - 110 watts (G6, G7, G9, G10 & G11)
45 watts - 90 watts (G8)
INPUT POWER (RF) 10 mW min. into ≤2:1 VSWR
TEMPERATURE RANGE -30°C TO +60°C (Ambient air)
SUPPLY VOLTAGE 13.4 Vdc
CURRENT 29 Amps max. (26 A typical @ rated power, 13.4V) (G3)
29 Amps max. (21 A typical @rated power , 13.4V)(G6, G7, G9, G10 &
G11)
29 Amps max. (20 A typical @ rated power, 13.4V) (G8)
DUTY CYCLE Continuous
STABILITY Stable into 3:1 VSWR; all temp.,voltage,freq. 55 watts - 110 watts (G3)
or 45 watts - 90 watts (G6, G7, G9, G10 & G11) or 45 watts - 90 watts
(G8)
RUGGEDNESS AT HIGH
VSWR
No damage into open or shorted load.
1These specifications are intended to be used by service personnel during servicing. Refer to the appropriate Specification
Sheet for complete specifications.
LBI-38674L 3

DESCRIPTION
2.0 DESCRIPTION
The UHF Power Amplifier Assembly is a wide band RF power amplifier operating over
the 380-400, 410-430, 403-425, 425-450, 450-470, 470-494, and 492-512 MHz range
without tuning. Its main function is to amplify the 10 mW FM signal from the
Transmitter Synthesizer to the rated RF output at the antenna port. The output of the
Power Amplifier Assembly is adjustable from rated power to 3dB lower at the PA output
J104.
The assembly consists of a printed wiring board (A1) and associated components,
including a power module and three RF power transistors, mounted to the heat sink
assembly. The printed wiring board (A1) contains both the power amplifier circuitry and
the power control circuitry.
Unfiltered supply voltage, A+, for the power amplifier circuits enters the assembly via
feedthrough capacitor, C1. Power cable W4 routes the A+ from C1 to J103 on the PWB.
Filtered A+ voltage for the power control circuit enters the assembly via control cable
W13, which connects to the PWB at J201.
The Power Control circuitry sets the output power level by adjusting the PA Power Set
level. It keeps the output power constant despite variations in input power, power
amplifier gain, or temperature through the use of a feedback control loop in the PA
assembly.
4LBI-38674L

CIRCUIT ANALYSIS
3.0 CIRCUIT ANALYSIS
3.1 POWER AMPLIFIER
The power amplifier section of the PA Board consists of an Exciter, a Small Signal Gain
Stage, a Low Level Amplifier, a Driver, and the Power Amplifier Finals. All these gain
stages have an input and output impedance of 50 ohms. Figure 1 is a block diagram
showing the signal flow within the Power Amplifier Assembly.
3.1.1 Exciter (U7)
The Exciter stage uses a broadband silicon monolithic microwave integrated circuit
(MMIC) amplifier. The signal from transmitter synthesizer, typically 10 dBm (10 mW),
is input to the Exciter through a 10 dB resistive pad (R1, R2, and R31). The Exciter
amplifies the resulting 0 dBm (1 mW) signal to 12 dBm (16 mW).
The MMIC requires a 5 volt supply source. The 8 volt regulator (U100) provides the 5
volts to the MMIC via a dropping resistor R30.
3.1.2 Small Signal Gain Stage
The Small Signal Gain Stage consists of Q7 and its associated bias and matching
circuitry. Collector voltage is fed through R39, R40, and L23. Resistor R33 sets the
quiescent bias of the part. The transistor input impedance is matched to the 50-ohm
output of the Exciter by C59, C61, C62, and L7. L23 and C49 provide the necessary
output matching. The stage provides 14 dB of gain to amplify the signal from the Exciter
to 26 dBm (400 mW).
3.1.3 Low Level Amplifier (U1)
The Low Level Amplifier (LLA) stage uses a 50 ohm thick film RF Power Module to
amplify and control the output power. Internally, the module is a three stage amplifier.
The power control circuitry controls the gain of the first and second stages by varying the
collector voltage level of Q203. The third stage gain remains constant with A+ providing
the DC supply voltage.
The signal from the Small Signal Gain stage, typically 26 dBm (400 mW), is input into
the LLA. Under typical Power Set conditions, the LLA amplifies the signal to a typical
output level of 40.5 dBm (11.2 W).
3.1.4 Driver (Q1)
The driver is a 6 dB RF amplifier consisting of transistor Q1 and its associated circuitry.
The signal from the LLA, typically 40.5 dBm (11.2 W), is amplified to 46.5 dBm (45.0
W). The transistor input is matched to 50 ohms by C65, C66, C27, C67, and a piece of
printed transmission line. The drive signal is then split with a printed in-phase Wilkenson
splitter, providing equal power to each of the final devices.
LBI-38674L 5

CIRCUIT ANALYSIS
3.1.5 Power Amplifier Finals (Q2 & Q3)
Each of the Power Amplifier final devices is capable of producing 5 to 6 dB of gain. The
output signal from the Splitter is impedance-matched to each of the finals. Under
optimum conditions each final amplifies the input signal to between 50 and 70 watts
output power (depending on band split). The outputs are then impedance-matched to the
input of the Combiner. The Combiner is a printed in-phase Wilkinson type, which
combines (sums) the output power of the finals. This produces an output power of
approximately 100W (depending on band split), which is coupled to the directional
coupler (part of A1 PWB) and on to the antenna circuits. In addition, the directional
coupler samples both forward and reverse power and sends this sample to the Power
Control circuitry.
16 dB
12 dB
Q7
SMALL SIGNAL
GAIN STAGE
PAD EXCITER
U1
LOW LEVEL AMPL
10W
Q1
DRIVER
=40W
SPLITTER FINALS
Q2 & Q3
6 dB =20W
=20W
5.0 dB
5.0 dB
=60W
=60W
COMBIMER
DIRECTIONAL
COUPLER
REV FWD
J104
RF OUT
130W (G3)
110W (G6, G7, G9, G10 & G1
1
90W )(G8)
THERMAL
SENSE
POWER
CONTROL
CONTROL VOLTAGE
PA KEY
FILTER A+
(4-8V) POWER SET
(2.5-4V) POWER SENSOR
-10 dB
J101
RF IN
10mW
* All power data is per miminum spec. Nominal Voltage (13.4V), 50 Ohm Load,
Room Temperature.
J1
J2
L
P
F
ANTENNA
Figure 1 - Block Diagram
3.1.6 Low Pass Filter
Following the Directional Coupler, the RF signal passes through a CHEBYSHEV LC
Low Pass filter (19D902856G3&G9). This passive circuit attenuates any residual
harmonics from the transmit carrier frequency and routes the signal through the RF
output to the antenna. Specifications for this filter are as follows:
Parameter Specifications for Group 3 Specifications for Group 9
Frequency (MHz) 376-470 MHz 470-512 MHz
RF Power Handling (W) 150 Watts 150 Watts
Insertion Loss (dB) 0.4 dB 0.5 dB
Input (VSWR) 1.5:1 Maximum 1.5:1 Maximum
Output (VSWR) 1.5:1 Maximum 1.5:1 Maximum
Harmonic Attenuation (dB) 50 Minimum 760-1500 40 Minimum 940-1024
30 Minimum >1500 MHz 30 Minimum > 1500 MHz
6LBI-38674L

CIRCUIT ANALYSIS
3.2 POWER CONTROL
The Power Control circuitry performs three basic functions. It keys and unkeys the PA,
sets the PA output power, and protects the PA against adverse conditions.
3.2.1 Keying and Unkeying the PA
To key the PA, the digital controller places 5 volts on the PA key line, J201-2. Zero volts
on the PA key line causes the PA to unkey. If the control cable (W13) is disconnected,
with nothing actively driving the PA key line, the PA will remain unkeyed.
3.2.2 PA Output Power Set
PA output power is set according to the level of the Power Set line. Four (4) volts on this
line will produce minimum power. As the voltage increases toward eight (8) volts, the
power will increase to its maximum rated output. The PA output power is initially set at
the factory. This is done by adjusting R43* while injecting a 10 mW signal at J1 and
applying 8 volts to J201-3. After setting the maximum power level, changing the output
power is done by varying the voltage applied on the Power Set line.
CAUTION
*Misadjustment of R43 may result in PA failure.
3.2.3 PA Protection
The Power Control also protects the PA against over temperature and high VSWR
conditions.
An over temperature condition exists when the flange temperature of the final output
transistor reaches 80°C. At this point the output power will drop below its set level. The
output power will continue to drop such that when the flange temperature reaches 125°C
the PA output drops at least 10 dB below its set level.
Reflected power is limited to 25% of the set power. If the output VSWR degrades to
worse than 3:1, the forward power will be reduced to limit the reflected power to 25% of
the set power. The Power Sensor line indicates when the PA is operating in a cutback
condition. If the PA is keyed and the power control is cutting back, the Power Sensor line
will drop to zero (0) volts and the PA alarm light on the station will turn on.
3.2.4 Theory of Operation
Power control of the MASTR® III Power Amplifier is accomplished with a feedback
control loop. The three possible feedback signals are: representation of forward power,
temperature sensitive scaled representation of forward power, or representation of
reflected power. These three signals are input to a diode summing junction which selects
the largest of the three for use as the feedback.
LBI-38674L 7

CIRCUIT ANALYSIS
The microstrip directional coupler samples the output power and produces a voltage, Vf,
proportional to the forward output power. The power control compares the forward
voltage, Vf, to a reference voltage at U3. The output of U3 controls the current flow thru
Q5 and the output of Q203. The collector output of Q203 adjusts the control voltage,
Vct1 and Vct2. This control voltage is capable of adjusting the total PA output power
since it provides the first two stages DC supply to the Low Level Amplifier, U1.
During over-temperature operation, a scaled representation of the forward power is
maintained constant by varying the control voltage line. Thermal resistor RT1, sensing an
increase in temperature, causes the output of U3.1 to increase. If the output of U3.1
becomes larger than the other feedback lines, the output of U3.4 will begin to decrease.
This in turn will cause the output of Q203 to decrease reducing the supply voltage to U1.
Since the scaling is a function of temperature, the power is reduced as the temperature
increases.
Under VSWR cutback operation the reverse voltage, Vr, representative of the reflected
output power, is held below a threshold by reducing the control voltage as necessary. If
Vr increases at U3.2 beyond the preset threshold, an increase at U3.4 will result. This
causes a subsequent reduction in the control voltage to U1. Thus the power control circuit
reduces the output power in order to limit the reflected power to 25% of the set power.
3.2.5 Signal Interface
The signal interface to the MASTR III Power Amplifier is supported by a six position
feedthrough connector, J201, with the following pinout:
1. PWR Sensor
2. PA Key
3. PA PWR Set
4. NC
5. Ground
6. Fil A+
3.2.5.1 Pwr Sensor
This line indicates when the PA is experiencing adverse conditions. Under normal
operation, while the PA is keyed, this line will be proportional to forward power.
Minimum power (zero watts) corresponds to 2.5 volts while maximum power
corresponds to 4.5 volts. This voltage is not temperature compensated and no effort is
made to calibrate this signal to an absolute power level. It is intended to provide a relative
indication of forward power and to discriminate between normal and cutback operation.
Zero volts on this line, when the PA is keyed, indicates the forward power is cutback.
This power cutback may be due to high reflected power or may be due to high PA
temperatures. This fault condition may indicate a problem with the PA or may indicate a
system problem external to the Power Amplifier. High VSWR may be due to a poor
antenna and high temperature may be due to a blocked cabinet vent. Zero volts on this
line, when the PA is keyed, does not indicate zero forward power. Zero volts indicates the
PA is protecting itself due to adverse conditions. If the adverse condition, either high
VSWR or high temperature is eliminated, the power will return to normal and the PWR
SENSOR voltage will rise above 2.5 volts.
8LBI-38674L

CIRCUIT ANALYSIS
3.2.5.2 PA Key (Interface Connector pin 2)
This line is used to key and unkey the PA. UNKEY = 0 volt and KEY = 5 volts. The
driver of this line must be capable of supplying 5 volts at 1.0 mA. The appropriate key
sequence requires RF from the transmit synthesizer be input to the PA before the KEY
line is energized.
3.2.5.3 PA PWR Set (Interface Connector pin 3)
This line is used to set the RF Power Output of the PA. Minimum power output equals 4
volts and maximum power output equals 8 volts. The driver of this line must be capable
of supplying 8 volts at 1.0 mA.
3.2.5.4 Fil A+ (Interface Connector pin 6)
This line provides the filtered supply voltage for the Power Control. The driver of this
line must be capable of supplying 13.4 volts ±20% at 100 mA.
LBI-38674L 9

TROUBLESHOOTING
4.0 TROUBLESHOOTING
4.1 TROUBLESHOOTING GUIDE
SYMPTOM AREAS TO CHECK INDICATIONS
1. Measure the transmitter output
power before the duplexer or
antenna switch (for simplex
mode).
The presence of power at this port
is an indication of a defective
duplexer, switch, or cables.
2. Measure the transmitter output
power before the low pass
filter.
The presence of power at this port
is an indication of a defective filter
or cables.
1. No Power or low Power at
Antenna Port.
3. Measure the transmitter output
power before the optional
isolator at the PA output port.
The presence of power at this port
is an indication of a defective
isolator or cables.
2. No power at PA output port
and PA ALARM is OFF.
Station is in receive mode.
1. No RF input to PA. Check
connection between PA and
TX
TX Synthesizer should deliver a
minimum of 10 Mw
2. Check the logic or DC inputs to
the PA from the Interface
Board through J201.
a. J201-2 PA KEY 5volts during transmit
b. J201-3 POWER SET 4 volts to 8 volts (4 volts
represents zero RF power)
c. J201-6 13.8 VF 13.8 Vdc ±20%
3. No power at PA output port
and PA ALARM is ON
3. Defective PA Replace PA
4. Low power at PA output port
and PA ALRAM is OFF.
1. Low RF input to PA from TX
Synthesizer.
Power should be a minimum of 10
mW (10 dBm).
2. Check the voltage on J201-
3(POWER SET).
For minimal output power, this
voltage should be above 7 volts.
3. Check the power supply
voltage on the collector of Q1,
Q2 and Q3
Voltage should be minimal 13.4
Vdc.
4. One of the two final PA
transistors (Q2 or Q3) is
defective.
Replace the defective transistor.
5. Low power at PA output port
and PA ALARM is ON.
Check for over temperature
and/or a high VSWR condition
due to a mismatch at the
output port.
The power control circuit protects
the PA by cutting back the power.
In case of a mismatch, refer to
symptom 1.
10 LBI-38674L