User's Manual

044-05156 Rev C 26
4.6 MCR21929-1-2 Amplifier Subrack
4.6.1 Overview
The MCPA system is a linear, feed-forward power amplifier system that operates in the 60 MHz frequency band
from 1930 to 1990 MHz with an instantaneous bandwidth of 20 MHz. It consists of an amplifier subrack with up to
two 125-watt G3S-1900-125 plug-in amplifiers.
The MCR21929-1-2 houses an RF power splitter/combiner and a control module that monitors the functional status
of all plug-in amplifiers. Additionally, the subrack is equipped with an Automatic Power Control (APC) circuit and an
RF GAIN ADJUST potentiometer. The APC indicator and GAIN ADJUST potentiometer are located on the upper
front of the subrack as shown below. Each subrack provides two RS-485 alarm interface ports, a preamp alarm
interface port, a Form-C alarm interface port and an RS-232 maintenance port, as well as, RF IN, RF OUT and a
–50dB RF sample port. Only the two RS-485 alarm interface ports are used to report alarm status to the SIM.
Subrack alarms are daisy chained together and address switches on the front panel are set to identify the
appropriate sector.
When two of the same model amplifiers are used, the system offers up to 218 watts of output power (after combiner
insertion losses) using the 125-watt amplifier.
MCR21929-1-2 (Reach-through (Pseudo) Front Access) - This 19-inch flush mount subrack has front “reach
through” access to its interconnect panel located at the rear of the subrack.
4.6.1.1 Controls, Indicators, & Interfaces
The location and function of the amplifier subrack controls and indicators is depicted below and described in the
paragraphs that follow.
MCR21929-1-2 Controls and Indicators
4.6.1.1.1 AO A3 (Address) Switch
This four-position DIP switch is used for setting the external RS-485 alarm bus address.
MCR21929-1-2 Address Switches
4.6.1.1.2 Config Switch
This four-position DIP switch is used for selecting software features in the amplifier subrack. Refer to Gain Modes
later in this section for a description. Preamplifiers are not used in this system, so the second dip switch is set to
Off, as indicated below in the left two diagrams.