Wavecom W61PC V7.5.0 - Manual (Page 227)

WAVECOM Decoder W61PC/LAN Manual V7.5 Transmission Modes  217
SITOR-ARQ
SITOR-ARQ is a simplex system where both stations transmit alternately on the same frequency.
The CCIR recommendation 476-3 defines a cycle of 450 ms and the two stations are designated as fol-
lows:
 ISS - information sending station
 IRS - information receiving station
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).