Wavecom W74PC V8.7.0 - Manual (Page 248)

238

Transmission Modes WAVECOM Decoder W74PC, W-PCI/e, W-CODE, W-CLOUD Manual V8.7.0
The WAVECOM software always decodes the information of the ISS station.
Parameter Value
Frequency range HF
Operation modes Simplex ARQ
Modulation FSK
Symbol rate 100.0 Bd
Shift/Bandwidth 170 Hz
Receiver settings DATA, CW, LSB or USB
Input format(s) AF, IF
SITOR systems almost exclusively operate at a symbol rate of 100 Baud and with a shift of 170 Hz.
After the receiver has been correctly tuned, the SITOR mode may be started by selecting a baud rate.
Fully automatic tuning to the signal center and shift may be achieved by selecting the Auto button.
The SITOR 7 bit alphabet employs a 3:4 mark-space ratio. The ISS transmits blocks of 210 ms duration
each containing 21 bits. In turn the IRS transmits acknowledgement bursts with a duration of 70 ms.
If the ISS does not receive an acknowledgement, a block containing the RQ character is sent. In the case
of blocks being received in error by the IRS, the last data block sent is repeated.
SITOR-AUTO
Fully automatic tuning to signal center, shift and transmission modes SITOR-ARQ (Mode A) and SITOR-
FEC (Mode B) may be achieved by selecting SITOR-AUTO mode.
SITOR-FEC
The SITOR-FEC mode is used in broadcast applications where a return channel is not required or unavaila-
ble. Two sub-modes are in use: General broadcasting to a number of stations and selective addressing of
only one station.
Parameter Value
Frequency range HF
Operation modes FSK, Broadcast/Simplex FEC
Modulation FSK
Symbol rate 100.0 Bd
Receiver settings DATA, CW, LSB or USB
Input format(s) AF, IF
SITOR-FEC transmissions are used in maritime radio communication to distribute traffic lists, news, safety
and weather information. Amateurs also use the FEC mode for calls to all (CQ calls).
The selective FEC is used when the receiving station must operate under "radio silence" conditions and
hence cannot transmit.
In most cases SITOR-FEC transmissions uses a rate of 100 Baud using the standard shift of 170 Hz.
Each character is transmitted twice with an interval of 35 bits. In the case of error-free reception of both
characters, the character is displayed on the screen. The underscore (_) character is displayed if both
characters are received in error.