User Manual

G3S-800-140-031 Installation & Service Manual
 Copyright Powerwave Technologies, Inc., September 2001. All rights reserved
044-05095 Rev. A 4-1 September 2001
Section 4 Principles of Operation
4-1 Introduction
This section contains a functional description of the Multicarrier Cellular Amplifier.
4-2 RF Input Signal
The maximum input power for all carrier frequencies should not exceed the limits specified in ta-
ble 1-2. For proper amplifier loop balance, the out of band components of the input signals
should not exceed -40 dBc. The input VSWR should be 2:1 maximum (or better).
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. If the amplifier is operated into a filter, it will maintain its distortion
characteristics outside the signal band even if the VSWR is infinite, provided the reflected power
does not exceed one watt. A parasitic signal of less than one watt incident on the output will not
cause distortion at a higher level than the normal forward distortion (i.e. -60 dBc).
4-4 G3S-800-140-031 Amplifier Module
The G3S-800-140-031 amplifier is a linear, feed-forward power amplifier that operates in the 25
MHz frequency band from 851 MHz to 869 MHz. The amplifier modules are designed for parallel
operation to achieve high peak power output, and for redundancy in unmanned remote locations.
The amplifier module, figure 4-1, has an average output of 140 watts power (1400 watts peak
power) with intermodulation products suppressed to better than -60 dBc below carrier levels. The
amplifier provides an amplified output signal with constant gain and phase by adding approxi-
mately 30 dB of distortion cancellation on the output signal. Constant gain and phase is main-
tained by continuously comparing active paths with passive references, and correcting for small
variations through the RF feedback controls. All gain and phase variations, for example those
due to temperature, are reduced to the passive reference variations. Each amplifier module has
an alarm and display board that monitors the amplifier performance. If a failure or fault occurs in
an amplifier module, it is displayed on the individual amplifier front panel.
The amplifier module is comprised of:
Predistorter
Pre-amplifiers
Main amplifier
Error amplifier
Two feed-forward loops with phase-shift and gain controls
DC/DC power regulator
Alarm monitoring, control and display panel
The main amplifier employs class AB amplification for maximum efficiency. The error amplifier
and feed forward loops are employed to correct signal nonlinearities introduced by the class AB
main amplifier. The error amplifier operates in class AB mode. The RF input signals are ampli-
fied by a preamp and coupled to an attenuator and phase shifter in the first feed-forward loop.
The main signal is phase shifted by 180 degrees and amplified in the premain amplifier. The out-
put from the premain amplifier is fed to the class AB main amplifier. The output from the main
amplifier is typically 220 watts. The signal is output to several couplers and a delay line.