ISC 9T97A250 User Manual
REVB
9T97A250 450-MHz Power Amplifier
User Manual
9110.00118
Copyright 2005 ISC Technologies
Table of Contents
1 GENERAL
2 RESERVED
3 DESCRIPTION
3.1 Front Panel Display and Alarms
3.2 Features
3.3 Physical Description
4 P. A. CIRCUIT AND LOGIC CIRCUIT DESCRIPTIONS...
4.1 Power Amplifier Circuit Description
4.2 Logic Circuit Description
5 INSTALLATION
5.1 Overview
5.2 Cabinet Installation
5.3 Operating and Servicing Hazards
5.4 Checks and Adjustments
5.5 Equipment Needed
6 ADJUSTMENTS
6.1 Power Amplifier Alignment and Tuning
6.2 Logic Alignment
Copyright 2005 ISC Technologies
1 GENERAL
This manual is intended for use by experienced technicians familiar with RF communication
systems. It contains all the necessary information required to align, install, interface, and
operate the 9T97A250 UHF Power Amplifier.
Any questions regarding the equipment or this manual should be directed to Customer Service.
ISC Technologies
One Glenayre Way Ste. 2
Quincy, IL
62301
Phone: (217) 221-0985
Fax: (217) 221-9775
2. Reserved
3 DESCRIPTION
The 9T97A250 UHF power amplifier is designed for FM operation in the 406 to 470 MHz
band. The RF power output is continuously adjustable from 50 watts to 250 watts when
driven by a 4-watt source. The RF input and output connectors are the type N panel mount
(UG-58 AN) and are mounted on the rear of the power amplifier. Input dc power is fed to
the power amplifier through a two-terminal barrier strip on the rear of the power amplifier. A
15-pin D-connector (for monitoring the power amplifier’s operating condition using its
associated test set) is mounted near the barrier strip. Forced air circulation is through the
front panel, using an internally controlled dc fan. The power amplifier is self-protected
against overheating and mismatched load conditions (including open and short circuit
conditions).
DANGER !
RF power transistors and RF termination resistors contain beryllium oxide. Beryllium
oxide fumes ARE TOXIC! No treatment should be attempted without proper
precautions. Disposal via public waste is strictly forbidden!
3.1 Front Panel Display and Alarms
Power Output Bar-Graph Indicates relative output power in ten levels (red).
RF Input LED Indicates RF input power is applied (green).
High VSWR LED Indicates an alarm due to high reflection at the output (red).
High Temperature LED Indicates an alarm due to over heating (red).
Power On LED Indicates that the dc supply is applied to the power amplifier (green).
Copyright 2005 ISC Technologies
3.2 Features
The 9T97A250 power amplifier has the features listed below.
• Adjustable power output.
• Continuous operation.
• Mounts on a 19-inch standard EIA rack panel.
• Self-resetting protection circuitry.
• Modular construction.
• Status and power output display.
• Easy access to amplifiers and protection circuitry for adjustment.
• Independent fusing of each final module and the driver with open fuse
indicator on the rear panel.
3.3 Physical Description
The 9T97A250 UHF power amplifier is rack panel mountable (19-inch). Front and rear
covers are removable to gain access to all controls without removing the 9T97A250 from
the rack.
The front panel display consists of a red LED bar-graph display showing output power. Two
red and two green status LEDs are also located on the front panel.
The rear panel consists of an RF input connector, an RF output connector, a DB-15
connector, and a two-terminal barrier strip for dc power connections.
4 P. A. CIRCUIT AND LOGIC CIRCUIT DESCRIPTIONS
4.1 Power Amplifier Circuit Description
4.1.1 General
The RF input, which is sampled by the alarm logic, is amplified by the RF power driver. The
driver’s net RF power output is varied by adjusting the dc voltage supply. The driver’s
power output is split into four parts which become the input power to each final. Each final
amplifies this input power and the output from the finals are combined and filtered. The
alarm logic samples both the output forward power and reflected power.
4.1.2 Driver
The driver module has two functions. Its primary function is to provide a variable power
input to the final power amplifier module, so that the net output power of the final amplifier
can be adjusted. The second function is to provide a sampling point for the alarm logic at
the input power point to the power amplifier.
The driver uses a MOS-FET transistor (Q1) with two dies in one package, operated in
push-pull configuration. R2 and R3 provide zero bias at the gates of Q1 for class C
operation. T1 and T2 are 1:1 balun transformers. Capacitor C4 at the input of the driver is
adjusted to fine tune the input match to 50 ohms, thereby minimizing input standing wave
reflection. Capacitor C16 couples a small amount of input power through diodes D1 and
D2. This dc voltage, which is proportional to the RF input, is fed to the alarm logic. The
rectified RF at the anode of D1 is smoothed by capacitor C17 and loaded by resistor R1.
The main part of the RF input goes through T1, C2, C3, Z1 and Z2 and capacitors C1, C4
and C5 match the transistor’s input impedance across the frequency band. Power (3-5 Vdc)
is fed via a “fast-on” tab to the drains of transistor Q1.
Matching of the transistor’s output impedance across the frequency band is provided by Z3,
Z4, C6. C7 and C10. Capacitors C5 and C9 are for dc blocking.
Copyright 2005 ISC Technologies
4.1.3 Splitter
The splitter consists of three splitters to provide a four-way divider. Each splitter is a ninety
degree hybrid and a 50-ohm load. A ninety degree hybrid is a length of wire line in this
case. The length is determined by the frequency band of the power amplifier. The wireline
is a form of semi-rigid 50-ohm coax that has two center conductors insulated from each
other.
Within the useable bandwidth, each hybrid splits the RF power into approximately two
equal parts that differ in phase by about ninety degrees. As the split and phase differ, some
power is dissipated in the load resistors terminating the fourth port of the hybrids. When
power is reflected from any other port, the bulk of this reflected power (nominally half) is
dissipated in the load. The remaining power is split equally between the other two ports.
The process of splitting and combining is very phase sensitive. Incorrect phasing will result
in power wastage, increased heat through power dissipation, reduced MTBFs. and reduced
output power. As a result, all cables between the splitter and the finals, and the combiner
must be exactly the same length. The necessary phase adjustments for manufacturing tolerances are provided by the tuning capacitors in the finals.
4.1.4 Final
All final modules are identical, only one module is described. The final module amplifies the
output of the splitter to about 65 watts and feeds this to the combiner.
The final is a common emitter class C amplifier. The transistor’s (Q1) input impedance is
matched to 50 ohms across the frequency bandwidth using micro striplines Z2, and Z3,
with capacitors C2, C3, C17, C5, and C6. Power (28 Vdc) is fed via a faston tab to the
collector of transistor Q1 through a dc-coupling network. Matching of the transistor’s (Q1)
output is provided by Z4, Z3, C8, C9, C10, and C18. In addition, C12 fine tunes the output.
4.1.5 Combiner
Like the splitter, the combiner consists of three ninety-degree combiners providing a fourway combiner. Each combiner is a ninety degree hybrids and a 50-ohm load. A ninety degree hybrid is a length of wireline in this case. The length is determined by the frequency
band of the power amplifier. The wireline is a form of semi-rigid 50-ohm coax that has two
center conductors insulated from each other.
Within the useable bandwidth, each hybrid combines the approximately equal RF feeds
(each feed differs in phase by about ninety degrees), into one. As the phase differs, some
power is dissipated in the load resistor terminating the fourth port of the hybrid. The resistive load’s most important function in the combiner is to dissipate the bulk of any reflected
power (nominally half). The remainder of the reflected power is split equally between the
other two ports (typically).
4.1.6 Low Pass Filter and Directional Coupler
The low pass filter attenuates the harmonics generated by the power amplifier. The directional coupler samples, and detects output power and reflected power. These signals are
then passed to the alarm logic. The output of the combiner is fed through the low pass filter
(C1, C2, C3, C4, L1, L2, and L3) and the directional coupler to the power amplifier’s output
connector. The directional coupler consists of three micro striplines Z1, Z2, and Z3 with
loads and detector circuits at both coupled ports. The directional coupler provides about -33
dB of coupling at the center frequency. Schottkey diodes (D1 and D2) are used for detection of forward and reflected RF power.
Copyright 2005 ISC Technologies
Loading...