Sitor-arq, Sitor-auto, Sitor-fec – Wavecom W61PC V7.5.0 User Manual

Page 227

WAVECOM Decoder W61PC/LAN Manual V7.5

Transmission Modes

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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

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.