User's Manual

044-05xxx Rev A 4-1
Chapter 4
Principles of Operation
4-1 Introduction
This chapter contains functional descriptions of the G3L-929-135 Multi-Carrier Power Amplifier
(MCPA).
4-2 RF Input Signal
The maximum input power for all carrier frequencies to the MCPA should not exceed the limits
specified in Table 1-1
4-3 RF Output Load
For good power transfer to the RF load, the load impedance should be as closely matched to the
output impedance of the MCPA as possible. A VSWR of less than 1.5:1 across the working band
of frequencies is satisfactory. If the MCPA is operated into a filter, it maintains its distortion
characteristics outside the signal band even if VSWR is infinite. 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 Functional Description
The MCPA is a linear, feed-forward amplifier that operates in the frequency band from 935 MHz
to 940 MHz with an instantaneous bandwidth of less than 5 MHz. Instantaneous bandwidth is the
maximum frequency band that a set of two or more signals can occupy .The MCPA’s
instantaneous bandwidth is set automatically and does not require manual setup. The MCPA
provides a gain of 63 dB. Typical outputs for different carrier types are specified in Table 1-1.
Each MCPA module is self-contained and functionally independent of any other MCPA in a
system. The MCPAs are designed for parallel operation to achieve a high peak power output.
Each MCPA has an alarm board that monitors performance. If a failure or fault occurs, it is
transmitted to the subrack via the module rear connector. The sub-rack reports all alarms to the
host system.
Continuously comparing active paths with passive references, and correcting for small variations
through RF feedback maintains constant gain. All gain variations, for example those due to
temperature, are reduced to the passive reference variations.
Refer to Figure 4-1 for the amplifier functional block diagram. The amplifier consists of the
following major functional blocks:
• Preamplifier
• Main amplifier
• Error amplifier
• Alarm monitoring and control
• First and second loop control circuits
• Pilot tone generator