Wavecom W-SPECTRA (Automatic Monitoring System) V1.1.0 - Manual (Page 190)

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Transmission Modes WAVECOM Monitoring System W-SPECTRA, W-SPEED Manual V1.1.0
At the end of transmission, a certain bit pattern (in hexadecimal notation, 4B65A5B2, MSB first) is sent to
mark the end of message (EOM). The EOM sequence is followed by the flush bits, which are for the FEC
coder flushing and for the complete transmission of the remainder of the interleaver matrix data block.
Therefore both the EOM sequence and the flush bits are treated as normal user data bits and passed to
the last interleaver block.
 Preamble (0.6 s or 4.8 s)
 Interleaver 1
 Interleaver 2
 ... ...
 Interleaver N (including EOM & flush bits)
Besides the FEC and interleaver used in this mode, a special component – the tone excision module – is
used to pre-process the waveform, so that a more stringent decoding performance can be reached than is
the case for the MIL-188-110A mode, even for a severely degraded HF radio link. The tone excision mod-
ule mainly adaptively eliminates interfering tones, which may occur during the transmission.
As in the MIL-199-110A mode, the raw user data transmitted by the NATO Robust mode is just binary.
Therefore the NATO Robust decoder displays the user data in BINARY, HEX, ASCII SYNC and two
ASCII ASYNC formats selected from Options | Message Type.... The decoder stops the display after
the EOM bit pattern is received and goes to the SYNC status for preamble hunting.
In the HEX display mode, the decoded binary data is just displayed as it is (MSB first).
In the ASCII SYNC mode, each 8 bits (LSB first) represent one ASCII character. The display will stop if the
EOM pattern is received or if more than 20 NULL characters are received.
There are two ASCII ASYNC display modes. In the first format (just named ASCII ASYNC) the 8 data bits
are preceded by one start bit (0) and followed by at least one stop bit (1). The 8 data bits (LSB first) form
an ASCII character. The second format (ASCII ASYNC, 7 Data bit, 0 Stop Bit) displays a 7-bit ASCII char-
acter (LSB first) which is preceded by one start bit (0). There is no stop bit in this format. In both modes
the decoder will stop displaying, in addition to upon receiving the EOM pattern, when more than 300 NULL
characters are received, when the async data structure is violated more than 80 times or the EOM bit pat-
tern is received.
Tuning the decoder
The decoder processes signals in both SSB settings, USB and LSB. This can be selected with the Polarity
setting in the menu: NOR will select USB and INV will select LSB.
The center frequency of the decoder should be set to 1800 Hz when the receiver is correctly tuned to the
transmitting station. Small frequency variations are automatically tracked and compensated for in the de-
coder. The center frequency of the decoder can be adjusted to ± 400 Hz from its normal setting. By using
the bar graph, any remaining frequency difference can be compensated for by fine-tuning of the receiver
frequency or by adjusting the center frequency of the decoder.
Related mode
MIL-188-110A
STANAG-4481-FSK
STANAG-4481 is a synchronous FSK mode, which uses KG-84 encryption for communication. It is com-
monly found in the HF band. A number of communication parameter settings are possible, but 75 Bd and
a shift of 850 Hz are widely used.
Parameter Value
Frequency range HF
Operation modes Broadcast/Simplex FEC
Modulation FSK
Baud rate 75, 100, 150, 300, 600 Bd
Receiver settings Data, CW, USB, LSB