CHAPTER 6
LINK-4A
INTRODUCTION
The Link-4A system is a fully automatic, high-speed data transmission system
used for aircraft control. The system provides controlling information to the aircraft,
using radio transmission between the controlling ship and the controlled aircraft. The
Carrier Aircraft Inertial Navigation System (CAINS) is also a part of the Link-4A
system. The CAINS system is used to load alignment and way-point data into the
aircraft on the flight deck or the hangar deck.
After completing this chapter, you should be able to:
. Describe the functions of the Link-4A system.
. Describe the operating modes of the Link-4A data terminal set.
. Describe the types of messages used by the Link-4A system.
. Describe the functional operation of the Link-4A data terminal
. Describe the test messages used in the Link-4A system.
LINK-4A SYSTEM OVERVIEW
The two major components of the Link-4A system
are the Link-4A CDS system and the CAINS system.
Both systems use serial time-division multiplexing to
transmit control and reply messages over a frequency-
shift keyed (FSK) UHF radio communications
channel. The CAINS system can also transmit data
via hard-wired stations on the flight deck or hangar
deck.
LINK-4A CDS SYSTEM
The Link-4A CDS system is used to provide one-
way or two-way communications between the
controlling station and up to 100 controlled aircraft.
The controlling station transmits to the aircraft control
messages containing vectoring information,
commands, and data pertaining to the target or
destination of the aircraft. The aircraft transmits reply
messages containing information concerning its
heading, altitude, airspeed, and tactical readiness. The
aircraft control messages are developed by the CDS
computer using radar-derived target data, reply data
from the aircraft, and other tactical data.
A typical shipboard Link-4A system configuration
is shown in figure 6-1. It consists of the CDS
computer, a data terminal set, a communications
switchboard, and a UHF radio transceiver.
The CDS computer outputs parallel digital data to
the Link-4A data terminal set. Currently, the data
terminal set most shipboard installations use is a type
of the AN/SSW-1 (U). It will be designated as the
AN/SSW-lA/B/C/D/E(U).
The
data
terminal
set
converts the computer data into a serial time-division
multiplexed pulse train that is transferred to the radio
transceiver through the communications switchboard.
The communications switchboard connects the
selected UHF transceiver to the data terminal set. The
radio transceiver converts the pulse train into FSK
variations in the carrier signal frequency.
After the aircraft receives the transmitted data, it
may respond by transmitting data to the controlling
6-1
