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Transmission modes, Acars – Wavecom W-SPECTRA (Automatic Monitoring System) V1.1.0 User Manual

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Transmission Modes

WAVECOM Monitoring System W-SPECTRA, W-SPEED Manual V1.1.0

Transmission Modes

ACARS

Aircraft Communications Addressing and Reporting System (ACARS) is a carrier sensing, multiple access
packet radio system for aircraft communications. ACARS operates in the VHF band, mainly around 130
MHz, using 2400 bps NRZI coded coherent audio frequency MSK (Minimum Shift Keying - a particular form
of FSK) on AM to make use of standard aircraft AM communications equipment.

Parameter

Value

Frequency range

VHF

Operation modes

CSMA/CD packet ARQ system

Modulation

AM, SUB FSK

Symbol rate

2400 Bd

Center frequency

1800 Hz

Shift

1200 Hz

Receiver settings

AM, BW = 3 kHz

Input format(s)

AF, IF

Additional Info

ITA-5 with parity and block coding

Frequencies Europe: 131.725, 131.525, 131.825 MHz

Frequencies USA: 131.550, 130.025, 129.125, 131.475, 130.450,

131.125, 136.700, 136.750, 136.800 MHz

Frequency Japan: 131.450 MHz

To receive ACARS an omni-directional 108-136 MHz antenna, a VHF AM receiver (scanner) with 13 kHz
channel bandwidth and a corresponding AF output is necessary. As the ACARS packets are very short, turn
the squelch of the receiver OFF.

Speed selection is not available for ACARS as only one speed is in use (2400 Baud).

Processing of ACARS Messages

It is possible to do some interpretation of ACARS messages. The following options are available:

Reassemble multipart messages

This setting enables the reassembling of bigger messages which are sent in several parts. Instead of
showing each part separately, the message is shown as one single message when the last part has been
received. The message header is still shown separately for each part.

Parse ADS-C messages

This setting enables the parsing of ADS-C messages (Automatic Dependent Surveillance - Contract). When
an ADS-C message is received, it is decoded and the additional information is shown in the output win-
dow.