Software Module A - Wavecom W 4010 User Manual

[F1] SITOR AUTO
[F2] ARQ OR FEC ONLY
[F3] ALPHABET SELECTOR
[F4] FORWARD SEQUENCE
[F4]+[F3] REVERSE SEQUENCE
After the equipment is turned-on, EPROM A is enabled. The video display now tells you that the possibility
exists to set the parameters for the serial port, video interface or weather-fax setup. The key [F4] must be
used to choose ARQ-FEC.
Turn both knobs, filter and level, fully counter-clockwise and look for an ARQ signal. The level adjustment
serves as a tuning help because with it the tuning display goes to the center during block pauses and the
frequency deviation can be seen clearly. After tuning has been finished, it is recommended to return the lev-
el adjustment to its neutral position to enable the reception of very weak ARQ signals. The level adjustment
is not needed with FEC signals and is therefore switched off for this mode. Nearby undesired signals can be
nulled out with the filter; it can easily be seen on the tuning display when the filter Page 14 is optimally ad-
justed. Narrowing the filter bandwidth is always an advanced FEC signals. If this is not desired, then one of
these modes can be selected. LSB or USB can be programmed since the software automatically recognizes
the signal polarity.
The [BU-ZI] key switches between RTTY letters/numbers should this happen to be false. The switch causes
no signal interruption, but is only effective when a signal is actually being received. The optimum FEC soft-
ware is also able to synchronize without the specially transmitted line end Rq-Idle repetition. This enables
synchronization without having to choose FEC-selective and FEC-collective.
SITOR is a simplex ARQ system where both stations alternately send on the same frequency. The CCIR Rec.
476-4 defines a period of 450 ms and the two stations are called: tage when strong, nearby signals or inter-
ference disturb the desired signal. In automatic mode, synchronization can be achieved with both ARQ and
FEC.
ISS Information Sending Station
IRS Information Receiving Station
The WAVECOM software always decodes the Information Sending Station.
The SITOR/AMTOR 7-bit alphabet uses a 3:4 mark to space ratio, however it is not identical to the alphabet
No. 3.
The Baud rate is always 100 Baud, i.e. 10 ms bit length.
The ISS sends 210 ms blocks of 21 bits.
The IRS sends 70 ms acknowledgement pulses.
The two IRS acknowledgement pulses, called CS1 + CS2, confirm error-free reception; the repetition of
the same control character tells the ISS to repeat the last block, respectively the last 3 characters.
If the ISS does not receive an acknowledgement, it sends an RQ block.
The following illustrates the transmission mode of both stations:
ISS 123456712345671234567
IRS
<——— 210 ms ————>
This mode is defined in CCIR Rec. 476-3, Mode B, and is a round table operation without an acknowledge-
ment to the transmitting station. The SITOR FEC has two ways of addressing the receiving stations: one is
the collective mode which transmits to many stations, the other is the selective mode which transmits to on-

3.2 SOFTWARE MODULE A

SITOR ARQ AND FEC
Automatic synchronization in both modes
Only synchronized with ARQ or FEC
Selects ITA-2, Cyrillic or Greek
go to next operating mode
go to previous operating mode
DEFINITION FOR SITOR-ARQ
123456712345671234567
1234567
<70 ms> <———— 210 ms ———>
SITOR FEC
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