User Manual

NTGS86AB Installation & Service Manual
Section 4 Principles of Operation
4-1 Introduction
This section contains a functional description of the NTGS86AB Single-Carrier Cellular Power
Amplifier module.
4-2 RF Input Signal
The maximum input power should not exceed the limits specified in table 1-1.
4-3 RF Output Load
The load impedance should be as good as possible (1.5:1 or better) in the working band for good
power transfer to the load.
4-4 Amplifier Functional Description
The NTGS86AB amplifier (figures 1-1 and 4-1) is a linear, single-channel power amplifier that
operates in the 25 MHz frequency band from 869 MHz to 894. The amplifier produces a typical
output power of 25 watts (44 dBm). Each amplifier in a system is a self-contained module and is
functionally independent of any other amplifier modules. Each amplifier module has alarms that
monitor the amplifiers performance. If a failure or fault occurs in an amplifier module, it is trans-
mitted to the host system via an RS-422 interface.
The amplifier is compliant to the requirements of FCC Part 24 with respect to spurious emissions
(see table 1-1). Constant gain is maintained by continuously comparing active paths with passive
references, and correcting for small variations through the RF feedback controls. All gain varia-
tions, for example those due to temperature, are reduced to the passive reference variations. The
amplifier module is comprised of:
• Input amplifier
• Pre-distortion amplifier
• Driver amplifier
• Main amplifier
• Isolator
4-4.1 Input Amplifier and Predistortion Amplifier
RF is fed to the input amplifier then to the predistortion amplifier where the input signal is dis-
torted such that it linearizes the output of the main amplifier. All the predistortion voltages and
loop voltages are controlled by a microprocessor.
4-4.2 Driver Amplifier
The driver amplifier is a class AB amplifier. The amplifier operates on +26 Vdc with bias voltage
controlled by the microprocessor.
 Copyright Powerwave Technologies, Inc., October 2002. All rights reserved
044-05126 Rev. A 4-1 October 2002