M/A-Com 19D902797G1 User manual

TABLE OF CONTENTS
Page
DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Front Cover
SPECIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
CIRCUITANALYSIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
POWER AMPLIFIER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Exciter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Low Level Amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
PA Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Drive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Power Amplifier Finals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
POWER CONTROL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Theory of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Signal Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
TROUBLESHOOTING GUIDE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
IC DATA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
PARTS LIST . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
PRODUCTION CHANGES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
POWER AMPLIFIER ASSEMBLY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
LOW PASS FILTER MODULE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
OUTLINE DIAGRAMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
POWER AMPLIFIER SCHEMATIC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
136-174 MHz, 110 WATT POWER AMPLIFIER
19D902797G1
DESCRIPTION
The VHF Power Amplifier Assembly is awide band RF
power amplifier operating over the entire 136 to 174 MHz
range without tuning or band splitting. Its main function is
to amplify the 10 mW FM signal from the Transmitter
SynthesizertotheratedRFoutputof110 watts at theantenna
port. The output of the Power Amplifier Assembly is adjust-
able from 65 to 135 watts at the PA output J104. This
corresponds to a rated RF output of 55 to 110 watts at the
antenna.
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 assem-
bly. The printed wiring board (A1) contains both the power
amplifier circuitry (100 series components) and the power
control circuitry (200 series components).
Unfiltered supply voltage, A+, for the power amplifier
circuits enters the assembly via feedthrough capacitor, C1.
Power cable W4 routes the A+ from CI 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.
Maintenance Manual
LBI-38531G
M/A-COM Wireless Systems
3315 Old Forest Road
Lynchburg, Virginia 24501
(Outside USA, 434-385-2400) Toll Free 800-528-7711
www.macom-wireless.com Printed in U.S.A.

CIRCUIT ANALYSIS
POWER AMPLIFIER
The power amplifier section of the PA Board consists of
an Exciter, a Low Level Amplifier, a Driver, and the Power
AmplifierFinals.Allthesegainstageshaveaninputandoutput
impedance of 50 ohms. Figure 1 is a block diagram showing
the signal flow within the Power Amplifier Assembly.
Exciter (UIOI)
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 (R100 &
R102). The Exciter amplifies the resulting 0 dBm (1 mW)
signal to 20 dBm (100 mW). Following the Exciter is a 3 dB
resistive pad (R104 & R106). This attenuator reduces the
MMIC output power to 17 dBm (50 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 R103.
Low Level Amplifier(U1O2)
TheLowLevelAmplifier(LLA)stage usesa50 ohm thick
film RF Power Module to amplify and control of the output
power. Internally, the module is a two stage amplifier. The
power control circuitry controls the gain of the first stage by
varying the collector voltage of Q203. The second stage gain
remains constant with A + providing the DC supply voltage.
The signal from the Exciter stage, typically 17 dBm (50
mW), is input into the LLA. Under maximum Power Set
conditions, the LLA amplifies the signal to a typical output
level of 40 dBm (10 W).
Driver (Q101)
The driver is a 6 dB RF amplifier. Anetwork consisting of
C114, C117 and C139 and L103 and L105 provides interstage
impedance matchingbetween U102 andQ101.The signal from
the LLA, typically 40 dBm (10 W), is amplified to 46 dBm (40
W). Impedance matching between the driver output and the
input to U103 is provided by C145, C148, C152, C153, and
L108. The splitter, U103, is a quadrature 90° hybrid coupler. It
divides the signal and applies equal power to the two Power
Amplifier Finals, Q102 and Q103.
Copyright© 1992-2002, M/A-COM Private Radio Systems, Inc. All rights reserved.
TABLE 1 - GENERAL SPECIFICATIONS
ITEM SPECIFICATION
FREQUENCY 136 MHz - 174 MHz
OUTPUT POWER 65 watts - 135 watts (into Low Pass Filter)
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. (25 A typical @ 135W, 13.4V)
DUTY CYCLE Continous
STABILITY Stable into 3:1 VSWR; all temp. ,voltage, freq. 65 watts -
135 watts
RUGGEDNESS AT HIGH VSWR No damage into open or short load.
Figure 1 - Block Diagram
This manual is published by M/A-COM Private Radio Systems, 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 Private Radio Systems, Inc., at any time and without notice. Such changes will be incorporated 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 Private Radio Systems, Inc.
LBI-38531G
1

Power Amplifier Finals (Q102, Q103)
Each of the Power Amplifier Final devices is capable of
producing 5.5 dB of gain. The output signal from the Splitter
is impedance matched to each of the finals. Under optimum
conditions each final amplifies the 43 dBm (20 W) power
input signal to 48.45 dBm (70 W) output power. The outputs
are then impedance matched to the input of the Combiner,
U104. The Combiner is a quadrature 90° hybrid coupler
which combines (sums) the output power of the finals. This
produces an output power of approximately 51.3 dBm (135
W)whichiscoupledthroughC 140tothedirectionalcoupler
(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.
POWER CONTROL
The Power Control circuitry performs three basic func-
tions. It keys and unkeys the PA, sets the PA output power,
and protects the PA against adverse conditions.
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 PAkey 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.
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.
ThePAoutputpoweris initiallyset for anoutputof135watts
at J104. This is done by adjusting R217 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.
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 willcontinue 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.
Theory of Operation
Power control of the MASTR III Power Amplifier is
accomplished with a feedback control loop. The three possi-
ble 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.
The stripline directional coupler samples the output
power and produces a voltage, Vf, proportional to the for-
ward output power. Thepower control compares theforward
voltage, Vf, to a reference voltage at U201D. The output of
U201D controls the current flow thru Q202 and the output
of Q203. The collector output of Q203 adjusts the control
voltage, Vct1. This control voltage is capable of adjusting
the total PAoutput power since it provides the first stage DC
supply to the Low Level Amplifier, U102.
During over temperature operation, a scaled repre-
sentation of the forward power is maintained constant by
varying the control voltage line. Thermal resistor R209
sensing an increase in temperature causes the output of
U201A to increase. If the output of U201A becomes larger
thantheotherfeedbacklines,theoutputofU201Dwill begin
to decrease. This in turn will cause the output of Q203 to
decrease reducing the supply voltage to U102. Since the
scaling is a function of temperature the power is reduced as
the temperature increases.
Under VSWR cutback operation the reversevoltage, Vr,
representative of the reflected output power is held below a
threshold by reducing the control voltage as necessary. If Vr
increases at U201B beyond the preset threshold an increase
at U201D will result. This causes a subsequent reduction in
the control voltage to U102. Thus the power control circuit
reducestheoutputpowerin ordertolimit the reflectedpower
to 25% of the set power.
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 - POWER SENSE
2-PAKey
3 - POWER SET
4-NC
5 - Ground
6-13.8VF
Power Sense
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 toan
absolute power level. It is intended to provide a relative indi-
cation of forward power and to discriminate between normal
and cutback operation.
Zero volts on this line, when the PAis keyed, indicates the
forward power is cutback. This power cutback may be due to
high reflected power (VSWR) or may be due to high PA
temperatures. This fault condition may indicate a problem with
the PAor 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, thepower will return
to normal and the PWR SENSOR voltage will rise above 2.5
volts.
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.
Power 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.
13.8 VF (Interface Connector pin 6)
Thislineprovidesthefilteredsupply voltageforthePower
Control. The driver of this line must be capable of supplying
13.8 volts ±20% at 100 mA.
LBI-38531G
2

SYMPTOM AREAS TO CHECK INDICATIONS
1. No Power or low Power at
Antenna Port 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. Measuer 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.
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 1. Station is in receive mode.
3. No power at PA output port and
PA ALARM is ON. 1. No RF input to PA. Check connection between PA and TX Synthesizer. TX Synthesizer should deliver a minimum of 10 mW (10 dBm) to the PA.
2. Check the logic or DC inputs to the PA
from the Interface Board through J201.
a. J201-2 PA KEY 5 volts 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. Defective PA Replace PA
4. Low power at PA output port
and PA ALARM 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 nominal output power, this voltage should be above 6 volts.
3. Check the power supply voltage on
the collector of Q101, Q102 and Q103. Voltage should be nominal 13.4 Vdc.
4. One of the two final PA transistors
(Q102 or Q103 is defective. Replace the defective transistor.
5. Low power at PA output port and
PA ALARM is ON. 1. Check for over temperature and/or a high VSWR condition due to a mis-
match 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.
TROUBLESHOOTING GUIDE PARAMETER
(50 OHM, -30°TO +60°C) REFERENCE
SYMBOL READINGS (volts DC)
SUPPLY VOLTAGE A+ 13.4 V ±20%
CONTROL VOLTAGE Vct 1 0 - 12 V
FORWARD VOLTAGE Vf 3 - 7 V
REVERSE VOLTAGE Vr 2 - 6 V
POWER SENSE J201-1 2.5 - 4 V
PA KEY J201-2 5 V
POWER SET J201-3 4 - 8 V
13.8 VF J201-6 13.8 V ±20%
VHF POWER AMPLIFIER VOLTAGE CHART
REFERENCE
SYMBOL @ 136 MHz (volts DC) @ 150 MHz (volts DC) @ 162 MHz (volts DC) @ 174 MHz (volts DC)
Vct1 7 - 10 V 6 - 8 V 4 - 6 V 4 - 6 V
Vf 5 - 7 V 5 - 7 V 5 - 7 V 5 - 7 V
Vr 2 - 3 V 2 - 3 V 2 - 3 V 2 - 3 V
J201-1 2.5 - 4 V 2.5 - 4 V 2.5 - 4 V 2.5 - 4 V
J201-3 6 - 8 V 6 - 8 V 6 - 8 V 6 - 8 V
J201-6 13.4 V 13.4 V 13.4 V 13.4 V
VHFPOWER AMPLIFIER TYPICALVOLTAGE READINGS
(50 ohm, room temperature, 13.4 Vdc supply voltage, and 110 watt output)
RATED POWER FOR MASTR III VHF BASE STATION
STANDARD WITH
DUPLEXER WITH ISOLATOR WITH DUPLEXER AND ISOLATOR
110W 75W 95W 70W
LBI-38531G
3

U100
19A705532P2
VOLTAGE REGULATOR
U101
344A3221P1
MMIC AMPLIFIER
U102
19A70532P1
PA AMPLIFIER MODULE
IC DATA PARTS LIST
LBI-38531G
4

PARTS LIST & PRODUCTION CHANGES
PRODUCTION CHANGES
Changes in the equipment to improve or to simplify circuits are identified by a
"Revision Letter", which is stamped after the model number of the unit. The
revision stamped on the unit includes all previous revisions. Refer to the Parts
List for descriptions of parts affected by these revisions.
REV. A - POWER AMPLIFIER 19D902797G1
To improve reliability. Replace C131, C132, C135 & C136 with
19A700006P37. Printed circuit board also changed.
REV. B - POWER AMPLIFIER 19D902797G1
To meet ETSI specs for adjacent channel transient power. Changed
R224 from 10K ohms (19B800607P103) to 22K ohms
(19B800607P223). Added D211 (19A700025P6) between Q201-C
(cathode) and Q201-E (anode).
REV. A - POWER AMPLIFIER MODULE, 19D902797G1
REV. A - POWER AMPLIFIER BOARD 19D902794G1
To improve reliability.
Changed capacitors C131, C132, & C136.
REV. B - POWER AMPLIFIER BOARD 19D902794G1
To meet ETSI specs for adjacent channel transient power.
Changed resistor R224. Resistor R224 was 19B800607P103, 10k
ohms.
Added Zener diode D211 between transistor Q201-C (cathode) and
Q201-E (anode).
REV. B - POWER AMPLIFIER MODULE 19D902797G1
REV. C - POWER AMPLIFIER BOARD 19D902794G1
To replace transistor Q101, no longer manufactured by vendor and to
improve final PA stability.
Added capacitors C118 and C301-C304.
Added ferrite beads L301-L304.
Deleted resistors R104 and R106. Resistors R104 and R106 were
19B800607P331, 330 ohms.
Changed capacitor C114. Capacitor C114 was 19A705108P19, 18pF.
Changed capacitors C132 and C135. Capacitors C132 and C135 were
19A700006P37, 130pF.
Changed capacitor C141. Capacitor C141 was 19A705108P120,
1000pF.
Changed inductor L106. Inductor L106 was 19A701418P1.
Changed inductors L119 and L120. Inductors L119 and L120 were
19A129569P1.
Changed resistors R105 and R214. Resistor R105 was
19B800607P100, 10 ohms. Resistor 214 was 19B800607P103, 10k
ohms.
Moved diodes D203, D205, D206, D209 and D210.
Moved connectors J101, J103 and J201.
Changed Printed Wire Board (PWB) from 19D902793P1R5 to
19D902793P1R6.
LBI-38531G
5

POWER AMPLIFIER ASSEMBLY
19D902797G1
(19D902797, Sh. 1, Rev. 14)
(19B801659, Sh. 2, Rev. 3)
POWER AMPLIFIER ASSEMBLY
19D902797G1
(19D902797, Sh. 2, Rev. 14)
ASSEMBLY DIAGRAM
LBI-38531G
6

ASSEMBLY, OUTLINE & SCHEMATIC DIAGRAMS
LOW PASS FILTER MODULE
19D902856G1
(19D902856 Sh. 1, Rev. 1)
LOW PASS FILTER MODULE
19D902856G1
(19D902853, Sh.1, Rev. 2)
(19D902854, Comp. Side, Rev. 9A)
LBI-38531G
7

OUTLINE DIAGRAM
POWER AMPLIFIER BOARD A1
19D902794G1 REV. C AND LATER
(19D902794, Sh.1, Rev. 18)
POWER AMPLIFIER BOARD A1
19D902794G1 REV. B AND EARLIER
(19D902794, Sh 1, Rev 15)
LBI-38531G
8

POWER AMPLIFIER ASSEMBLY
19D902797G1
(19D902798, Sh. 1, Rev. 9)
SCHEMATIC DIAGRAM LBI-38531G
9

SCHEMATIC DIAGRAM
POWER AMPLIFIER ASSEMBLY
19D902797G1 REV. B AND EARLIER
(19D902798, Rev. 4)
LBI-38531G
10

POWER AMPLIFIER ASSEMBLY
19D902797G1 REV. C AND LATER
(19D902798, Rev. 9)
SCHEMATIC DIAGRAM LBI-38531G
11