Ericsson 19D902797G3, 19D902797G7, 19D902797G6 Maintenance Manual

LBI-38674C

Printed in U.S.A.

TABLE OF CONTENTS

DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Front Cover

SPECIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

CIRCUIT ANALYSIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

POWER AMPLIFIER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Exciter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Small Signal Gain Stage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Low Level Amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Driver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Power Amplifier Finals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

POWER CONTROL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Theory of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Signal Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

TROUBLESHOOTING GUIDE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

BLOCK DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

POWER AMPLFIER READINGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

ASSEMBLY DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

PARTS LIST . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

IC DATA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

OUTLINE DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

ASSEMBLY DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

SCHEMATIC DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

LOW PASS FILTER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

MAINTENANCE MANUAL FOR

450-470 MHz, 110 WATT POWER AMPLIFIE R

19D902797G3

425-450 MHz, 90 WAT T POWER AMPLIFIER

19D902797G7

403-425 MHz, 90 WAT T POWER AMPLIFIER

19D902797G6

DESCRIPTION

The UHF Power Amplifier Assembly is a wide band RF

power amplifier operating over the 403-425, 425-45 0 and
450-470 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 componen ts, includ ing a power modu le 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.

CIRCUIT ANALYSIS

POWER AMPLIFIER

The power amplifier section of the PA B oard 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.

Exciter (U101)

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 throug h a 10 dB re s ist i v e pad (R 1, R 2, a nd
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.

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 C63.
L24 provides the necessary output matching. The stage pro­vides 14 dB of gain to amplify the signal from the Exciter to
26 dBm (400 mW).

Low Level Amplifier (U102)

The Low Level Amplifier (LLA) sta ge uses a 50 ohm thick
film RF Power Module to amplify and control of 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).

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.

Power Amplifier Finals (Q2, Q3)

Each of the Power Amplifier Final devices is capable of
producing 5.2 (G3) [5.0 ( G6, G7)] dB of gain. The output
signal from the Splitter is impedance matched to each of the
finals. Under optimum conditions each final amplifies the

43.3 dBm (21 W) (G3) [43.0 d Bm (2 0W) (G6, G7)] power
input signal to 48.45 dBm (70 W) (G3) [48.0 dBm (63W)
(G6, G7)] output power. 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 51.1 dBm (130 W) (G3) [50.5 dBm (110W)
(G6, G7)] 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.

POWER CONTROL

The Power Control circuitry pe rforms three basic func­tions. 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 P A, the digital controller places 5 vo lts 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.

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)

Copyright © July 1992, Ericsson GE Mobile Communications Inc.

Table 1 - General Specifications

ITEM SPECIFICATION

FREQUENCY 450 MHz - 470 MHz (G3)

403 MHz - 425 MHz (G6)
425 MHz - 450 MHz (G7)

OUTPUT POWER (RF) 65 watts - 130 watts (G3)

55 watts - 110 watts (G6, G7)

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 @ 130W, 13.4V) (G3)

29 Amps max. (21 A typical @ 110W, 13.4V) (G6, G7)
DUTY CYCLE Continuous
STABILITY Stable into 3:1 VSWR; all temp.,voltage,freq. 65

watts - 130 watts (G3) or 55 watts - 110 watts (G6, G7)
RUGGEDNESS AT HIGH VSWR No damage into open or shorted load.

Figure 1 - Block Diagram

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volts, the power will increase to its maximum rated output.
The PA output power is initially set for an output of 130 watts
(G3), 110 watts (G6, G7) at J104. 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 in 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 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.

Theory of Operation

Power control of the MASTR III Power Amplifier is
accomplished with a feedback control loop. The three possi­ble feedback signals a re: representat ion of forward p ower,
temperature sensitive scaled representati on 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, pro portional to the for­ward output power. Th e power con trol compares the f orward
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 U3.1 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.

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+

Pwr Sensor

This line indicates when the PA is experiencing adve rse
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.

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 approp riat e key seq uenc e
requires RF from the transmit synthesizer be input to the PA
before the KEY line is energized.

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 m aximum power
output equals 8 volts. The driver of this line must be capable
of supplying 8 volts at 1.0 mA.

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.

SYMPTOM AREAS TO CHECK INDICATIONS

1. No Power or low Power at 1. Measure the transmitter output The presence of power at this
Antenna Port. power before the duplexer or port is an indication of a

antenna switch (for simplex defective duplexer, switch, or
mode). cables.

2. Measure the transmitter output The presence of power at this
power before the low pass filter. port is an indication of a

defective filter or cables.

3. Measure the transmitter output The presene of power at this
power before the optional isolator port is an indication of a
at the PA output port. defective isolator or cables.

2. No power at PA output port 1. Station is in receive mode.
and PA ALARM is OFF.

3. No power at PA output port 1. No RF input to PA. Check TX Synthesizer should deliver
and PA ALARM is ON. connection between PA and TX a minimum of 10 mW

Synthesizer. (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 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. Defective PA Replace PA

TROUBLESHOOTING GUIDE

LBI-38674

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SYMPTOM AREAS TO CHECK INDICATIONS

4. Low power at PA output port 1. Low RF input to PA from TX Power should be a minimum
and PA ALRAM is OFF. Synthesizer. of 10 mW (10 dBm) .

2. Check the voltage on J201-3 For nominal output power,
(POWER SET). this voltage should be above

7 volts.

3. Check the power supply voltage Voltage should be nominal
on the collector of Q1, Q2 13.4 Vdc.
and Q3

4. One of the two final PA Replace the defective
transistors (Q2 or Q3) is transistor.
defective.

5. Low power at PA output port 1. Check for over temperature and/ The power control circuit pro­and PA ALARM is ON. or a high VSWR condition due to tects the PA by cutting back

a mismatch at the output port. the power. In case of a mis-

match, refer to symptom 1.

TROUBLESHOOTING GUIDE (cont’d)

FREQUENCY ADJUSTABLE WITH WITH WITH DUPLEXER

MHz STANDARD RANGE DUPLEXER ISOLATOR AND ISOLATOR

450-470 110W 65-130W 75W 100W 70W
425-450 90W 55-110W 60W 82W 55W
403-425 90W 55-110W 60W 82W 55W

RATED POWER FOR MASTR III UHF BASE STATION

PARAMETER REFERENCE READINGS

(50 ohm, -30°C to +60°C) SYMBOL (volts DC)

SUPPLY VOLTAGE A+ 13.4 V ±20%
CONTROL VOLTAGE Vct1 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%

UHF POWER AMPLIFIER VOLTAGE CHART

Group Low Mid High

Frequency G3

G6
G7

450 MHZ
403 MHZ
425 MHZ

460 MHZ
414 MHZ
437 MHZ

470 MHZ
425 MHZ
450 MHZ

Vct 1 (Volts DC) G3

G6
G7

7 - 10 Volts

6 - 8 Volts
6 - 8 Volts

6 - 8 Volts
6 - 8 Volts
6 - 8 Volts

4 - 6 Volts
6 - 8 Volts
6 - 8 Volts

Vf (Volts DC) G3

G6
G7

5 - 7 Volts
6 - 8 Volts
6 - 8 Volts

5 - 7 Volts
6 - 8 Volts
6 - 8 Volts

5 - 7 Volts
6 - 8 Volts
6 - 8 Volts

Vr (Volts DC) G3

G6
G7

2 - 3 Volts
2 - 3 Volts
2 - 3 Volts

2 - 3 Volts
2 - 3 Volts
2 - 3 Volts

2 - 3 Volts
2 - 3 Volts
2 - 3 Volts

J201 - 1 (Volts DC) G3

G6
G7

2.5 - 4 Volts

2.5 - 4 Volts
25 - 4 Volts

2.5 - 4 Volts

2.5 - 4 Volts
25 - 4 Volts

2.5 - 4 Volts

2.5 - 4 Volts
25 - 4 Volts

J201 - 3 (Volts DC) G3

G6
G7

6 - 8 Volts
6 - 8 Volts
6 - 8 Volts

6 - 8 Volts
6 - 8 Volts
6 - 8 Volts

6 - 8 Volts
6 - 8 Volts
6 - 8 Volts

J201- 6 (Volts DC) G3

G6
G7

13.4 Volts

13.4 Volts

13.4 Volts

13.4 Volts

13.4 Volts

13.4 Volts

13.4 Volts

13.4 Volts

13.4 Volts

UHF POWER AMPLIFIER TYPICAL VOLTAGE READINGS

(50 ohm, room temperature, 13.4 Vdc supply voltage, and rated output )

LBI-38674

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