RF Technology Eclipse PA220 User manual

Eclipse Series
RF Technology
[e-mail]
SEPTEMBER 2003
PA220 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 Pty Ltd

Page 2 RF Technology PA220
CONTENTS CONTENTS
Contents
1Operating Instructions 4
1.1 Installation 4
1.1.1
Sub-rack Wiring Guidelines
4
1.2 Front Panel Indicators 4
1.3 Internal Adjustments 5
1.4
Amplifier I/O Connections
5
1.4.1 RF Input 5
1.4.2 RF Output 5
1.4.3 25 Pin Connector 6
2Circuit Description 6
2.1 Amplifiers 6
2.2 Power Splitter / Combiners 7
2.3 Directional Coupler 7
2.4 Low Pass Filter 7
2.5 Power Control Circuits 7
2.6 RF Output Indicator 8
2.7 Over Temperature Protection 8
3Field Alignment Procedures 8
3.1 Output Power Level 8
3.2 Tuning Procedure 9
4Specifications 9
4.1 Description 9
4.2
Physical Configuration
10
4.3 Front Panel Indicators and Test Points 10
4.3.1 Indicators 10
4.3.2 Test Points 10
4.4
Electrical Specifications
10
4.4.1 Power Requirements 10
4.4.2 Frequency Range 10
4.5 Antenna Impedance 11
4.6 Output Power 11
4.6.1
Transmit Duty Cycle
11
4.7 Spurious and Harmonics 11
4.8 Heatsink Temperature 11
4.9 ALC Output 11
4.10 Connectors 11
4.10.1 RF Input 11
4.10.2 RF Output 12
4.10.3 25-Pin Connector 12
4.10.4 9-Pin Connector 12

RF Technology PA220 Page 3
CONTENTS CONTENTS
AEngineering Diagrams 12
A.1 Block Diagram 12
A.2 Circuit Diagrams 12
A.3 Component Overlay Diagrams 12
BParts List 17

Page 4 RF Technology PA220
1 OPERATING INSTRUCTIONS
1Operating Instructions
The PA220 is part of the Eclipse range of modular base station equipment. It is a power
amplifier capable of delivering 100 Watts in the VHF frequency range. It is designed
to complement the T220 transmitter, and mounts in a standard Eclipse sub-rack.
1.1 Installation
There are no front panel controls. In normal circumstances no alignment or setup is
required. If mounted in a sub-rack that has not previously been wired for a power
amplifier, the rack connector must be wired according to the guidelines in section 1.1.1
below.
1.1.1 Sub-rack Wiring Guidelines
When installing an Eclipse Power Amplifier in an Eclipse sub-rack, observe the
following guidelines for sub-rack installation:
•The sub-rack power supply must be capable of delivering the full current
requirements for all modules fitted in the sub-rack, typically 20 Amperes for a
100W transmitter/amplifier.
•Owing to the current drain, power supply lines should be cabled to the power
amplifier separately and using heavy gauge wire to minimise voltage drop and
interference via the power supply of other modules in the rack.
•
The ALC line from the power amplifier must be connected to the ALC input of the
exciter. If this connection is not correctly made, no control of the output power
level will be possible. This can result in excessive RF output power, and
consequent breach of licensing authority regulations, or possible overload of the
unit.
With an Eclipse T220, join pin 8(ALC) on the exciter and the amplifier.
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.

RF Technology PA220 Page 5
1OPERATING INSTRUCTIONS 1.2 Front Panel Indicators
1.2 Front Panel Indicators
PWR LED The power (PWR) LED shows that the dc supply is connected to the
transmitter.
RFO LED The RF output (RFO) LED indicates that the amplifier is being driven
and that the forward output power is above a preset level. This preset indication
level is generally set 1 - 3 dB below the preset output power level. The presetting
potentiometer RV2 is not accessible without removal of the cover plate.
TEMP LED The temperature (TEMP) LED indicates illuminates should the
amplifier's internal temperature become too high. The RF power is
automatically reduced if the internal temperature rises above safe limits.
1.3 Internal Adjustments
All internal adjustments are factory set and should not need to be changed under normal
conditions. A possible exception to this is the RF output power
level which may need
to be changed to comply with local licensing requirements. The
low forward power
warning circuit should be set at the same time as the forward power level.
WARNING
Ensure that the power setting complies with the
requirements of your licensing authority. Failure to do
so may result in penalties being imposed by the
licensing authority.
Output Power The output power is set by RV2. This is nominally set to 100 Watts
(+50dBm), but may be set to any value between 20 and 100 Watts depending
upon local regulations in the destination country. RV2 determines the threshold
affecting the ALC voltage that is fed back to the transmitter module to regulate
RF output power.
RF Level Detector The forward RF power threshold associated with the RFO LED on
the amplifier front panel is set by RV3. This is nominally set at half to three-
quarters of the preset output power.

Page 6 RF Technology PA220
1.4 Amplifier I/O Connections 2 CIRCUIT DESCRIPTION
1.4 Amplifier I/O Connections
The PA220 has three connectors on the rear panel.
1.4.1 RF Input
The RF drive is delivered via a BNC connector. The absolute maximum power that
should be applied to this connector is 25 Watts.
1.4.2 RF Output
The RF output signal is available from an N-type connector.
Pins Function
1, 2, 14, 15 Positive supply
12, 13, 24, 25
Ground (negative supply)
8ALC output
Table 1: Pin connections for the 25 pin “D” connector on the rear panel
Note: The amplifier is capable of delivering as much as 120 Watts continuously.
In certain conditions1an RF power of 130 Watts or more can be available via this
connector. This corresponds to peak voltages in excess of 100 while currents in
excess of 2 Amperes may flow. Appropriate care should be taken when working
on the PA220 to avoid making or breaking connections when the amplifier is
operating, and to avoid RF burns through close proximity to live connections, etc.
1.4.3 25 Pin Connector
The 25-pin “D” connector provides connection to ground and dc power, and from the
automatic level control (ALC) circuit. The pin connections are given in table 1. The
ALC line floats high to approximately 7Vdc. Pulling this line low will reduce output
power. Voltages below 0.5V will reduce the output by more than 20dB. A pull-down
current of approximately 1mA is required.
2Circuit Description
The following descriptions should be read as an aid to understanding the block and
schematic diagrams shown in figures 1 - 4.
_________________
1
Excessive powers may be available, for example, in the event of a failure of the ALC loop,
such as may arise if the ALC feedback connection is broken.

RF Technology PA220 Page 7
2CIRCUIT DESCRIPTION 2.1 Amplifiers
2.1 Amplifiers
The RF power amplification is provided by two single transistor amplifiers, Q1 and Q2.
Each amplifier is rated at 50 watts output. The input and output impedance of the
transistors is matched to 50Ωby broad band micro-strip matching networks.
Trimmer capacitors C10 and C24 are used on the input networks to optimize the input
match at center of the desired frequency range. Similarly C58 and C59 on the output
networks are used to optimize the output efficiency.
Since the design of the amplifiers allows them to be very broad band, they will not
usually require re-adjustment unless changing frequency from one end of the band to
the other.
The dc supply is fed to the amplifiers through resistors R27 and R28. This allows the
collector current of each amplifier to be measured at the test socket.
2.2 Power Splitter / Combiners
In the 100W models, zero-degree hybrid power splitter / combiners are used to parallel
the two amplifier stages. The hybrids consist of quarter-wave 70Ω
transmission lines
and 100Ω
RF resistors CX1-4, R9 and R10. This configuration provides wider
bandwidth and better balance than lower cost 90-degree hybrids.
2.3 Directional Coupler
The forward and reverse power components are measured through a coupled line
directional coupler. The output of the coupled line is frequency compensated by R13,
R14, C29 and C30 before being detected by D1 and D2.
The output of the detectors is proportional to the forward and reflected voltage
components.
2.4 Low Pass Filter
A low pass filter consisting of L12 - 14 and C39 - 42 reduces the harmonic components
to less than -80dBc. The filter uses a combination of lumped elements and printed
microstrips to obtain the required harmonic attenuation.
2.5 Power Control Circuits
The forward and reverse voltages from the directional coupler are amplified and
inverted by U1a and U1b. The amplified voltages are combined before connecting to
the input of error amplifier U1d.

Page 8 RF Technology PA220
2.6 RF Output Indicator 3 FIELD ALIGNMENT PROCEDURE
Error amplifier U1d compares the detected voltage with the dc reference voltage from
output power trimpot RV1. The amplified difference at the output of U1d is supplied to
the rear panel system connector for connection to the T220 ALC input.
Equipment Type Key Specifications
Power Supply 13.8Vdc,15A
RF Source 25 Watt (eg. T220 exciter)
RF Load / Attenuator 50Ω, 50/100W, SWR<1.2:1
RF Power Meter eg. HP437B or calibrated detector and voltmeter
Table 2:Standard test equipment for the PA220 Power Amplifier
2.6 RF Output Indicator
The forward power voltage is compared with the pre-set dc reference
voltage from RV2
by U1c. The output of U1c is used to turn on the RFO LED and provide an output
power logic signal to the test connector.
RV2 is normally set so that the RFO LED comes ON 1 - 3db below the nominal power
output level.
2.7 Over Temperature Protection
Thermistor RT1 is mounted to the case of output transistor Q1. If the transistor case
temperature rises above 90 Celsius the resistance of RT1 increases and Q5 is turned
ON.
This causes the TEMP LED to come on and also reduces the dc reference voltage to the
output power error amplifier U1d. The input power will then be reduced by the
transmitter ALC circuits and the output transistor is kept within safe operating limits.
3Field Alignment Procedures
3.1 Output Power Level
1. Set the unit up on a bench with the standard test equipment listed in table 2.
2.
Set RV1 and RV2 both fully counter-clockwise.
3. Set the exciter to the desired operating frequency.

RF Technology PA220 Page 9
4SPECIFICATIONS 3.2 Tuning Procedure
4.
Adjust RV1 to set the output power on the meter to the level at which you want the
RFO LED to illuminate.
5. Adjust RV2 until the RFO LED just goes out.
6. Adjust RV1 for the desired output power.
3.2 Tuning Procedure
Adjustment of the matching circuits is carried out with the aim of
•
ensuring that the specified power is available
•balancing the load reasonably equally between the power transistors, and
•
obtaining acceptable efficiency in the power transistors.
Note that the factory alignment procedure is complicated, but allows a given unit to
operate across a full 10% bandwidth, without further adjustment. Alignment without
appropriate equipment can leave the amplifier unstable or otherwise unable to meet
specification. However, the procedure below will usually provide adequate
performance.
1. Disconnect the ALC line.
2.
Set the RF source to deliver 15W at the highest frequency in the band over which
the PA is specified.
3. Measuring the RF output power, adjust C10, C24, C102, C112, C58, C59, C104 and
C114 to obtain maximum output.
4.
Measuring the collector currents of Q1 and Q2 at the test socket, adjust C58 and
C59 to reduce and balance the currents, but keeping the power above the required
level.
5. Proceed to carry out the power setting procedure in section 3.1.
4Specifications
4.1 Description
The PA220 power amplifiers are designed for use with the T220 series transmitters to
provide 100 Watts of RF output. Output power is regulated by connecting the ALC
output to the ALC input of the driving exciter. The drive from the transmitter module is
then automatically adjusted to maintain the required output.

Page 10 RF Technology PA220
4.2 Physical Configuration 4 SPECIFICATIONS
The regulated power level can be preset over a wide guaranteed range from 25 to 100
Watts or more, depending on the available input power and the model.
Sensing circuits are provided to protect the output transistors from excessive
temperature. If the heat sink temperature rises to 80C, the input drive will be reduced to
prevent damage.
4.2 Physical Configuration
The power amplifier is designed to fit in an RF Technology sub-rack within a 19" rack
frame. The installed height is 4 Rack Units (RU), or 178mm, and the depth is 350mm.
The amplifier is
95.25mm or three Eclipse units wide. The amplifier uses an extruded
aluminium heat sink with vertical fins. Heatsink temperature rise is typically 20C at
50W output.
4.3 Front Panel Indicators and Test Points
4.3.1 Indicators
Power: Green LED
RF Power:Yellow LED
Over Temperature:Red LED
4.3.2 Test Points
Forward Power:Voltage to ground, 0 - 4V, uncalibrated (pin 4 - gnd)
Reverse Power:Voltage to ground, 0 - 4V, uncalibrated (pin 3 - gnd)
Collector Currents:
Voltage to positive supply, across 0.1
Ω, ±10% (pins 7 - 1 and 8 - 1).
4.4 Electrical Specifications
4.4.1 Power Requirements
Operating Voltage:10.5 - 16 Volts, with output power reduced below 12.5V
Current Drain:16 Amperes maximum (14 typical) at 100 Watts and 13.5 Volts,
100mA maximum standby
Polarity: Negative Ground