Ericsson 19D901865G1, 19D901865G3, 19D901865G2 Maintenance Manual
LBI-38128
B
ericssonz
Ericsson Inc.
Private Radio Systems
Mountain View Road
Lynchburg, Virginia
1-800-528-7711 (Outside USA, 804-528-7711)
Printed in U.S.A.
TABLE OF CONTENTS
PAGE
DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
CIRCUIT ANALYSIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
SCHEMATIC DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
OUTLINE DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
PARTS LIST . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
DESCRIPTION
The PA assembly uses five RF power transistors to provide
110 watts of output power, or 3 RF transistors to provide 40 watts
of output power. The output power is adjustable over a range of
55 to 110 watts in the high power PA, and 20 to 40 watts in the
medium power PA. Five tr ansistor s are us ed in the po wer contro l
circuit.
Supply voltage for the PA is connected fr om power leads on
the Transmit-Receive-System (TRS) board through feedthrough
capacitors A2-C1 and C2 to hole 11 (A-) an d hole 12 (A+) o n
the PA board. C52, C53, and L23, and L24 prevent RF from
getting on the power leads. Diode D5 will cause the main fuse in
the fuse assembly to blow if the polarity of the power leads is
reversed.
The PA assembly is insulated from vehicle ground by C33
through C44 to permit operation in positive or negative ground
vehicles.
PA metering Jack J1 is provided for use with GE Test Set
Model 4EX3A11 or Test Kit 4EX8K12 with a cable adaptor . The
Test Set meters the RF drive (exciter output), control voltage
driver current, PA current and PA voltage.
CIRCUIT ANALYSIS
RF AMPLIFIERS
The exciter output is coupled through P101 on the TRS
board to PA input jack J3. The RF is coupled through a 50 ohm
stripline (Z5) and then through T1, stripline Z6, L1 and Z7 to the
base of 1st RF Driver Q1.
Part of the RF is rectified by D1 and applied to RF Switch
Q13 to activate the power control circuitry. P art of the DC voltage
is applied to voltage dividers R1 and R2 for metering the exciter
output at J1.
The RF amplifiers consist of three Class C, common-emitter
amplifiers. In 40 watt transmitters, Q3 is the PA stage. R17, L12
and L42 are a stabilizing network in the base of Q3. The output
of Q3 is coupled through 50 ohm coaxial cable W6 to the low
pass filter and then to the antenna relay.
NOTE
In positive ground vehicles, A- is "hot" with respect to
vehicle ground. Shorting the transmitter PA printed
wiring board ground pattern to the radio case may cause
one of the in-line fuses to blow.
MAINTENANCE MANUAL
150-174 MHz, 110 WATT POWER AMPLIFIER 19D901865G1
136-174 MHz, 40 WATT POWER AMPLIFIER 19D901865G2,3
Driver current is metered at J1 (Driv er Current). The reading
is taken on the one-volt scale with the High Sensitivity button
pressed, and with the meter polarity switch in the minus (-)
position. The meter is read as 15 amperes full scale. Jumpers W3,
W5 and W7 act as shunt resistors for the metering circuit.
In 110 watt transmitters, the 40 watt output is coupled
through jumper W1 to a Wilkinson power splitter consisting of
C57, C59, L26, L27 and Z1.
The power amplifier stages consist of two identical paralleled Class C power amplifiers (Q5 and Q6).
L30, L32, R24 and C63 make up a stabilizing network in the
base of Q5, while L31, L33, R25 and C68 make up the stabilizing
network in the base of Q6. Supply voltage (A+) for Q5 and Q6
is coupled through collector feed networks Z3 and Z4.
Collector current for Q5 and Q6 is measured at J1 (PA
Current). The reading is taken on the one-volt scale with the high
sensitivity button pressed and the polarity switch in the minus (-)
position. The current is read as 30 amperes full scale.
The output of Q5 and Q6 is applied to a Wilkinson power
combiner consisting of C78, L40, Z2, L41 a nd C79. Th e ou t pu t
of the combiner is coupled through T2 and two 50 ohm striplines
(Z16 and Z17) to the low pass filter. The filter output is coupled
through 50 ohm stripline to Z18 to the antenna relay (K1).
POWER CONTROL CIRCUIT
The power control circuit provides power leveling as well
as thermal protection for the PA.
When the transmitter is keyed, RF is rectified by D1. The
resulting DC turns on RF switch Q13. This allows Q11, Q12 and
pass transistor Q4 to turn on. Turning on Q4 applies collector
voltage to 1st RF driver Q1.
If the power output should start to increase above the level
set by R23, Q14 will start to conduct. This causes Q12, Q11 and
Q13 to conduct less, reducing the collector voltage to the 1st RF
driver.
Thermal protection is provided by temperature compensating resistor R19. As the heat sink temperature rises above 70
o
C,
the resistance of R19 decrease s. Thi s c aus es Q3 , Q 11, an d Q1 2
to conduct less, reducing the power output.
Copyright© June 1988, General Electric Company
Do not operate the transmitter at levels higher than rated
output. Operating at higher than rated output will shorten the life of the RF power transistor.
CAUTION
The RF Power Transistors used in the transmitter contain Beryilium Oxide, A TOXIC substance. If the ceramic, or other encapsulation is opened, crushed,
broken or abraded, the dust may be hazardous if inhaled. Use care in replacing transistors of this type.
WARNING
LBI-38128
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