Si-Fec; Sitor-Arq - Wavecom W74PC Manual

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
Frequency range
Operation modes
Modulation
Symbol rate
Receiver settings
Input format(s)
Additional Info
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
Frequency range
Operation modes
Modulation
Symbol rate
Shift/Bandwidth
Receiver settings
Input format(s)
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.
WAVECOM Decoder W74PC, W-PCI/e, W-CODE, W-CLOUD Manual V9.1.0
Value
HF
Broadcast/Simplex FEC
FSK
96.0 and 192.0 Bd
DATA, CW, LSB or USB
AF, IF
ITA-3
Value
HF
Simplex ARQ
FSK
100.0 Bd
170 Hz
DATA, CW, LSB or USB
AF, IF
Transmission Modes  241