RF Technology 50A 25 - 50 MHz Base Station Transceiver User Manual Power amplifier operations manual

RF Technology Pty Ltd 25 - 50 MHz Base Station Transceiver Power amplifier operations manual

Contents

Power amplifier operations manual

Eclipse Series
RF Technology
rfinfo@rftechnology.com.au
November, 2001
PA50 Amplifier
Operation and Maintenance Manual
This manual is produced by RF Technology Pty Ltd
10/8 Leighton Place, Hornsby 2077 Australia
Copyright © 2001, RF Technology
Page 2 RF Technology PA50
CONTENTS CONTENTS
Contents
1 Operating Instructions 3
1.2 Front Panel Indicators 3
2 Internal Adjustments 3
3 Test Points 4
4 I/O Connections 4
5 Circuit Description 5
5.1 Driver Stage 5
5.2 Output Stage 5
5.3 Low Pass Filter 5
5.4 Bias Supply 5
5.5 Reflectometer 6
5.6 Metering Circuits 6
6 Specifications 7
6.1 Physical Configuration 7
6.2 Indicators and Test Points 7
6.3 Electrical Specifications 7
6.3.1 Power Requirements 7
RF Technology PA50 Page 3
1 OPERATING INSTRUCTIONS
1 Operating Instructions
The PA50 is part of the Eclipse range of modular base station equipment. It is a power
amplifier capable of delivering 120 Watts in the VHF frequency range. It is designed
to complement the T50 transmitter, and mounts in a standard Eclipse sub-rack.
1.2 Front Panel Indicators
PWR LED Power LED indicates that the PA50 is connected to a DC power source.
RFO LED RF Output LED indicates that the PA50 is being driven by the exciter
and RF Output is available at the antenna socket.
TEMP LED Temperature LED indicates that the output transistors are above 90
degrees. This is only an indication and not an alarm condition as the
exciter monitors the PA50 temperature at all times in order to keep
within safe operating limits.
2 Internal Adjustments
All internal adjustments are factory set and should not need to be changed under normal
conditions.
R238 Driver bias adjustment
R239 O/P Q101 bias adjustment
R240 O/P Q100 bias adjustment
R227 Forward power meter adjustment
R228 Reverse power meter adjustment
C209 Reflectometer balance adjustment
WARNING
Changes or modifications not expressly approved by RF
Technology could void your authority to operate this
equipment. Specifications may vary from those given in
this document in accordance with requirements of local
authorities. RF Technology equipment is subject to
continual improvement and RF Technology reserves the
right to change performance and specification without
further notice.
Page 4 RF Technology PA50
3 TEST POINTS
3 Test Points
These test points are provided on the PCB and the DB9 front panel connector for use by
maintenance personnel
TP100 and TP101 Driver drain current measurement. A multimeter placed across
these pins will indicate 1 volt for 1 amp of Q102 drain current
TP102 and TP103 O/P stage drain current measurement. A multimeter placed across
these pins will indicate 1 volt for 10 amps of Q100 and Q101
drain current
TP200 PA Temperature reading. 1 volt indicates a temperature of 40
degrees. This reading deviates by 10mV per degree of change
TP203 Reverse voltage output from the reflectometer
TP204 Forward voltage output from the reflectometer
DB9 pin 1 GND
DB9 pin 2 O/P drain current
DB9 pin 3
DB9 pin 4 Reverse voltage
DB9 pin 5 +28V
DB9 pin 6 Driver drain current
DB9 pin 7
DB9 pin 8 Forward voltage
DB9 pin 9
4 I/O Connections
There are 3 I/O connectors on the rear panel with the following functions
25 pin connector DC power and exciter logic interface
Pin 1,2,3,4,14,15,16,17 GND
Pin 10,11,12,13,22,23,24,15 +28V
Pin 7 DATA-IO
Pin 19 CLK
Pin 20 CS
Pin 18 VREFB
Pin 6 Forward Volts
Pin 8 Reverse Volts
Pin 9 Temperature
BNC Connector: RF Input from exciter, approximately1 Watt
N Connector: RF Output to antenna, up to 150 Watts
RF Technology PA50 Page 5
5 CIRCUIT DESCRIPTION
5 Circuit Description
The following descriptions should be read as an aid to understanding the block and
schematic diagrams.
5.1 Driver Stage
The function of the driver stage is to transform the RF input signal from the exciter to
the appropriate levels and impedance required by the output stage. The RF input signal
is applied to the high pass filter ( C121, C130, C131, C132, C133, L102 and L106 ).
This filter suppresses any residual low frequency spurious that may be present at the
exciter output. T100 is used to transform the nominal 50 ohm output from the exciter to
match the input of Q102. A negative feedback network ( C120, R130, R132, R131,
R133, R125, R129, L107 and R124 ) is used to achieve a reasonably flat gain across the
frequency of operation and to match the drive level requirements of the PA50 to the
output level provided by the exciter. DC bias is applied to the gate of Q102 via R120
and R121 and is decoupled by C106 and C116. The DC feed for Q102 drain is
decoupled by L100, C112, C102, C100 and C118. T101 is used for impedance matching
between the driver and output stage and to provide a balanced feed for the push-pull
output stage
5.2 Output Stage
The output stage amplifies the 5 – 10 W from the driver to in excess of 150 W for final
delivery into the low pass filter. Q100 and 101 are driven in push-pull configuration by
the outputs of T101. L105, R126, C126 and L104, R127, C127 form negative feedback
paths in order to achieve a reasonably flat frequency response across the frequency of
operation. T102 is used to provide the DC feed via the centre tap in the primary winding
to Q100 and Q101. T102 also combines the balanced output of the transistors into a
single ended output as well as provide the necessary impedance transformation from the
transistors into a nominal 50 ohms. A small DC bias is applied to the gates of Q100 and
Q102 via R118, 119, 122 and 123 and decoupled by C103, 113, 107 and 117. The DC
feed to the transformer is decoupled by L103, L101, C101, 119, 104, 114, 105, 115 and
128.
5.3 Low Pass Filter
The low pass filter attenuates spurious emissions to less than –86dBc.
5.4 Bias Supply
The function of the bias supplies is to provide a temperature compensated bias voltage
to the gates of Q100, Q101 and Q102 for adjustment to their quiescent currents. U205
and R213, R214 and R215 provide the bias voltages. U200D provides a decreasing
output voltage with increasing temperature. The resistive dividers R214, R229 and
Page 6 RF Technology PA50
5 CIRCUIT DESCRIPTION
R213, R230 and R208, R215 provide the bias voltage to the transistors so that quiescent
current is maintained across the operating temperature range.
5.5 Reflectometer
The reflectometer provides an indication of load mismatch. A200 is a current
transformer with a single turn primary being passed through the centre of a toroid. The
multiturn secondary has an output voltage that is proportional to the current flowing in
the primary. The voltages appearing at the anodes of D205 and D206 are of equal
amplitude and opposite phase. A sample of the line voltage is applied to the junction of
the divider resistors R218 and R220. C209 is adjusted for equal amplitude with the
transformer. Since the transformer has 180 degree phase shifted outputs, the application
of the line voltage will cause cancellation at D205 and addition at D206. This phase
relationship will change when a mismatch occurs resulting in an increase in the voltage
at D205. D205 and D206 rectify these voltages so that a DC level proportional to the
forward and reflected voltages are available for the metering circuits. L200 provides a
DC reference point for the diodes.
5.6 Metering Circuits
These circuits are included so that the exciter can interrogate the PA and read all the
vital operating levels. U203 is an A to D converter with the following inputs:
Reverse voltage
Forward voltage
Temperature
DC Input volts
O/P drain current
Driver drain current
Q100 bias voltage
Q101 bias voltage
Model identification jumpers
Forward and reverse voltages are supplied from the reflectometer outputs and factory
set to the correct levels by R227 and R228. U204 ( temperature sensor ) is mounted on
the same pad as the source lead of Q101 to provide a temperature reading of the O/P
transistor cases. DC Power Input voltage is provided by a resistive divider (R3 and R4).
The O/P drain current is provided by measuring the small voltage drop across R113 and
R128. Driver drain current is provided by measuring the small voltage drop across R112
and R138. The bias voltages are read directly from the bias supplies. The model
identification is determined by the jumper settings of J203, 204 and 205.
PA50A 25 – 32 MHz J203 on, J204 and J205 off
PA50B 30 – 40 MHz J204 on, J203 and J205 off
PA50C 38 – 50 MHz J205 on, J203 and J204 off
U202 and associated components provide a 3 wire serial interface to allow the exciter to
interrogate the A to D converter. U200C is a comparator that switches the fan on when
the temperature rises above 40 degrees C. U201D is a comparator that switches the
RF Technology PA50 Page 7
6 SPECIFICATIONS
TEMP LED on when the temperature rises above 90 degrees C. Q203 samples the line
output RF voltage to turn on the RFO LED.
6 Specifications
The PA50 is designed for use with the T50 exciter to provide 20 to 150 Watts output.
Output power regulation is performed by the exciter as it continually monitors PA
performance. The exciter also monitors important levels such as temperature, reverse
power and drain currents to keep them within operating limits.
6.1 Physical Configuration
The PA50 is designed to fit into a 19 inch rack mounted frame. The installed height is
4RU or 178mm and the depth is 350mm The amplifier is 125mm wide. An extruded
aluminium heatsink with vertical fins and an enclosed fan is used. The temperature rise
can be as high as 50 degrees depending on output power.
6.2 Indicators and Test Points
Power On Green LED
RF Power Yellow LED
Temperature 60 degrees + Red LED
Forward Power DB9 pin 8 and GND
Reverse Power DB9 pin 4 and GND
O/P Drain Current DB9 pins 2 and 5
Driver Drain Current DB9 pins 6 and 5
+28V DB9 pin 5
GND DB9 pin 1
6.3 Electrical Specifications
6.3.1 Power Requirements
Operating Voltage 26 to 30VDC ( available O/P power reduced below 26V )
Current Drain Approx 10A at 28V and 100W O/P
Polarity Negative Ground
Frequency Range PA50A25 to 32MHz
PA50B30 to 40MHz
PA50C38 to 50MHz
Page 8 RF Technology PA50
6 SPECIFICATIONS
Nominal Antenna Impedance 50 ohms
Output Power 20 to 100 Watts
Transmit Duty Cycle 100W Continuous up to 60 degrees C ambient
Spurious Emissions less than 0.25uW
Maximum Heatsink Temperature 110 degrees C
Mismatch Protection Protected from damage by control from the exciter
Connectors Antenna connector N type female on rear panel
Power and exciter interface DB25 Female on rear panel
RF Input BNC female on rear panel
Test connector DB9 female on front panel

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