INSTALLATION MANUAL
CMA-5024 GLSSU
This document includes Proprietary Information and shall not be reproduced or communicated to third party
without prior written permission by CMC Electronics Inc.
Page 17
November 21, 2008
H. GLSSU Electrical Description
Refer to the functional block diagram of the GLSSU, Figure 7.
The GLSSU accepts the 28 VDC aircraft power via pins in J1. The power supply module converts this
input to the internal DC regulated voltages, which power the CRA. The CRA accepts the RF signals
directly via J2 and provides DC power to the active antenna (not illustrated) with current limiting and
lightning protection. The CRA inputs/outputs data with the aircraft systems via the connectors J1 and J3
through the EMI Filter & Lightning assembly.
Energy storage devices in the GLSSU maintain operation during short power interruptions and glitches.
Built-in power monitors control the orderly turn-on and shutdown of the GLSSU.
The EMI filters in the interconnect assembly block spurious RF propagation in/out of the GLSSU for
preventing electromagnetic interferences. The interconnect assembly also contains lightning protection
circuitry to absorb the high-energy pulses caused by lightning strokes, in order to protect the electrical
components in the GLSSU. These devices protect the ARINC 429 and RS-232 inputs and outputs, and
the Time Mark outputs.
The HIS in the CRA operates from the GLSSU power supply and/or from a dedicated HIS power supply
assembly; typically feed from a high-integrity 28 VDC power input line, so that the HIS will keep
operating in case of single-point failures.
The remote antenna (not illustrated) must be compliant with RTCA/DO-301. Its RF pre-amplifier is
powered by a 9 VDC nominal voltage from the CRA, carried via the center conductor (+9 VDC) and the
shield (0 VDC) of the coaxial antenna cable. The CRA monitors continuously the presence and health of
the remote antenna and of its RF cable by means of DC continuity and DC current load tests.
The document reference is online, please check the correspondence between the online documentation and the printed version.
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