WAVECOM Decoder W74PC, W-PCI/e, W-CODE, W-CLOUD Manual V9.1.0
Transmission Modes
241
SI-FEC
The SI-FEC sound is similar to the sound of SITOR-FEC. However, SI-FEC is used very seldom and stations
mostly switch to this mode only under extremely poor propagation conditions.
Parameter
Value
Frequency range
HF
Operation modes
Broadcast/Simplex FEC
Modulation
FSK
Symbol rate
96.0 and 192.0 Bd
Receiver settings
DATA, CW, LSB or USB
Input format(s)
AF, IF
Additional Info
ITA-3
SI-FEC operates at symbol rates of 96 and 192 Bd on the radio link.
SI-ARQ stations can switch to FEC broadcasting operation in similarity to SITOR-ARQ (Mode A) and SI-
TOR-FEC (Mode B).
The SI-FEC mode uses the ITA-3 alphabet for data protection. Each character is sent twice, but with a
time delay. The repeated character is transmitted with inverted polarity.
For a pair of characters which have been decoded and recognized as error-free one character is displayed.
If both characters are received in error the underscore (_) character is displayed.
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.
