6802800U74-AN
Chapter 10: Base Radio
low-level signal is sent to the Power Amplifier where it is amplified to the desired output power level.
The PA is a continuous-keyed linear amplifier. A power control routine monitors the output power of the
Base Radio and adjusts it as necessary to maintain the proper output level.
For information on the performance specifications, see Technical Specifications on page 398.
NOTICE: The Base Radio is prepared for TEDS.
10.2.1
Transceiver (XCVR)
The transceiver provides the receive, transmit, and control functions for the Base Radio. The
transceiver consists of three elements:
• Receiver-performs the receive function
• Exciter-performs the transmit function
• BR Controller-performs the control function
The receiver incorporates three separate receiver channels for use in diversity reception. The bias for
the LNAs in the Preselectors is supplied by bias circuitry in the receiver. A +7 V dc voltage is the output
on the QMA receive input connectors.
The receiver performs highly selective bandpass filtering and dual down conversion of the station
receive RF signal. A custom receiver IC outputs the baseband information in a digital data format and
sends it to the Base Radio controller.
The exciter in conjunction with the Power Amplifier (PA), provides the modulation and transmitter
functions for the Base Radio.
The transceiver contains the Base Radio Controller (BRC). The BRC serves as the main controller of
the Base Radio. The BRC provides signal processing and operational control for the other Base Radio
circuit blocks.
The operating software and configuration data are contained within the BRC flash memory. The
software defines operating parameters for the BR, such as output power and operating frequency.
NOTICE: To protect the key encryption key in use in the infrastructure, it is recommended that
this key is overwritten using the Key Variable Loader (KVL) device (through the front serial port)
before shipping for repair.
IMPORTANT: BR-Arch-1 Base Radios: To avoid the risk of causing a high bit error rate to
occur, do not use 385.572 MHz and 419.175 MHz as receiving frequencies in the Base Radios
of the MTS.
10.2.2
Power Amplifier
The Power Amplifier (PA) in conjunction with the exciter provides the transmitter functions for the Base
Radio. The Power Amplifier accepts the low-power modulated RF signal from the exciter and amplifies
the signal for transmission through the RF output connector. Base Radios in BR-Arch-2 architecture
use single, high-power amplifiers capable of running efficiently in low-power settings.
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