User's Manual

Table Of Contents

G3L-1929- Installation and Service Manual

Section 4. Principles of Operation

4-1 Introduction

This section contains a functional description of the G3L-1929-120 Multi-Carrier Power Amplifier

(MCPA).

4-2 RF Input Signal

The maximum input power for all carrier frequencies to the amplifier should not exceed the limits

specified in the appendix A specifications.

4-3 RF Output Load

The load impedance should be as good as possible (VSWR of 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 re-

flected 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. –65 dBc).

4-4 Multi-Carrier Power Amplifier (MCPA) Functional Description

The MCPA is a linear, feed-forward multi-carrier power amplifier that operates in the 60 MHz fre-

quency band from 1930 MHz to 1990 MHz (refer to table 1-4 for amplifier specifications). The

amplifier provides a gain of 60 dB to provide a typical output of 70 watts (48.8 dBm). Refer to fig-

ure 4-1 for the amplifier functional block diagram. Each amplifier is a self-contained module and

is functionally independent of any other MCPA in a system. The amplifiers are designed for paral-

lel operation to achieve high peak power output. Each MCPA has an alarm board that monitors

the amplifier performance. If a failure or fault occurs in an MCPA, it is transmitted to a subrack

system via the D-subminiature 21WA4 connector at the rear of the module. The subrack reports

all alarms to the host system.

Continuously comparing active paths with passive references, and correcting for small variations

through RF feedback controls maintain constant gain. All gain variations, for example those due

to temperature, are reduced to the passive reference variations. The amplifier consists of the fol-

lowing major functions:

• Preamplifier

• Main amplifier

• Error amplifier

• Alarm monitoring and control

• First and second loop control circuits

• Pilot tone generator

044-05138 Rev. A 4-1 May 2003