User's Manual

NTUM30DA Installation & Service Manual
Section 4 Principles of Operation
4-1 Introduction
This section contains a functional description of the multichannel power amplifier (MCPA).
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 NTUM30DA amplifier (figures 1-1 and 4-1) is a linear, MCPA that operates in the 60 MHz
frequency band from 1930 MHz to 1990 MHz with an instantaneous bandwidth of 20 MHz. The
operating band is determined by the operating frequency selection(s) of the base station (refer to
table 1-1). The amplifier produces 45 watts of output power when operated in mode 1 or 30 watts
of output power when operated in mode 2. Each amplifier is a self-contained module and is func-
tionally independent of any other amplifier module(s) in the system. Each amplifier module has
an alarm board that monitors the amplifier performance. If a failure or fault occurs in an amplifier
module, it is transmitted to the host system via an RS-485 interface.
The amplifier is compliant to the requirements of FCC rules 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:
An input amplifier
1
st
Loop Phase & Gain
A driver amplifier
A main amplifier
A multifunction board
4-4.1 Input Amplifier
RF is fed to the input amplifier, which consists of an isolator at the input, bandpass filter, voltage
variable attenuators (VVA), and phase shifters for gain control and phase sweeping functions.
The circuits in this section of the amplifier are controlled by a microprocessor on the Multifunction
board. At its output, the input amplifier splits the signal to the 1
st
Loop Phase and Gain circuit, and
the carrier cancellation circuit.
4-4.2 1
st
Loop Phase & Gain
The 1
st
Loop Phase & Gain circuit is a predistortion amplifier. The input signal is predistorted
such that it linearizes the output of the main amp at the rated output power of the MCPA. It also
contains the main loop VVAs and phase shifters. All the predistortion voltages and loop voltages
are controlled by a microprocessor.
 Copyright Powerwave Technologies, Inc., June 2003. All rights reserved
044-05141 Rev. A 4-1 June 2003