WAVECOM Decoder W74PC, W-PCI/e, W-CODE, W-CLOUD Manual V9.1.0 Transmission Modes
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Systems (VTS) in congested areas such as harbors, rivers and archipelagos. Tranmissions may be in
broadcast mode or individually addressed. The messages may contain a fixed content in binary format,
free text or binary information defined by international, regional or national authorities (see table below).
Transmission is 9600 Baud GMSK modulation over 25 or 12.5 kHz channels using the HDLC packet proto-
col. Each station transmits and receives over two radio channels to avoid interference problems. Self-
Organizing Time Division Multiple Access (SOTDMA) is used. One Time Division Multiple Access (TDMA)
frame corresponds to one minute and contains 2250 slots.
Each frame contains an 8-bit ramp up and a 24-bit synchronization sequence. At the beginning and end of
each frame, a HDLC flag (01111110) is sent. After the 8-bit preamble, 168 bits of data and a 16-bit CRC
checksum are sent in a default packet (one slot). Long transmission packets may occupy two to five con-
tinuous slots. Bit stuffing and NRZI encoding is used.
Traffic can be monitored on the AIS1 Channel 87B 161.975 MHz and AIS2 Channel 88B 162.025 MHz
From Options | Display Mode, All frames or Error free frames may be selected.
AIS Binary Messages
0, 2, 3, 4, 5, 11, 12, 13, 14, 15, 16, 17
10, 21, 22, 23, 24, 40, 55
ALE-400
Amateur version of MIL-188-141A.
For more details see “MIL-188-141A” on page 193.
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