Wavecom W61PC V7.5.0 - Manual (Page 203)

WAVECOM Decoder W61PC/LAN Manual V7.5 Transmission Modes  193
In contrast to PACTOR, all data blocks are in consecutive order with no or little space between them. They
are several variants on the market. The baud rate is fixed to 100 or 200 Bd. PACTOR-FEC is used for
broadcast transmission and is recognized by the FSK Code Check or Classifier Code Check.
PACTOR-II
With PACTOR-II, a modern, narrow-band and reliable two-channel PSK mode is available, which covers
the needs of both amateur and professional users for a secure and fast data transmission system. The
good performance during disturbances and a small bandwidth of 500Hz are achieved by the use of a two
channel DPSK modulation. As propagation conditions change, PACTOR-II is able to select the most suita-
ble modulation (DBPSK, DQPSK, D8PSK, D16PSK and 16PSK) and the length of the frame (SHORT or
LONG). Under very poor conditions PACTOR-II changes to DBPSK short block, which has a frame duration
of 1.25 seconds and carries only a small amount of data. For very good conditions, D16PSK with a long
frame is used, which transfers a large amount of data and needs 3.75 seconds.
Parameter Value
Frequency range HF
Operation modes Simplex ARQ
Modulation Two channel DBPSK, DQPSK, D8PSK, D16PSK adaptive, 16PSK
Symbol rate 100.0 Bd
Automatic frequency control (AFC): ± 50 Hz
Receiver settings DATA, CW, LSB or USB
Input format(s) AF, IF
Additional Info ITA-5 with block coding
HEX (Binary Output)
7.035 MHz, 14.070 MHz
To achieve a data transmission which is robust against all kind of disturbances, a decision must be made,
whether a short or a long frame-length should be used. The resulting input bit stream is then terminated
with a convolutional encoded and interleaved CRC-sum. After that, the symbol mapping for the two chan-
nels is done, and then this signal is applied to the DPSK or PSK demodulator.
To extract the data from a PACTOR-II signal, the signal is received and demodulated with a two channel
demodulator. The center frequency must be adjusted to the center between the two channels. To achieve
the best performance, the AFC (automatic frequency control) should be enabled. After the demodulation
and the bit synchronization, the symbols of the two channels are combined to one bit stream. After the
modulation type has been determined, the resulting bit stream is de-interleaved, passed through a
Viterbi-decoder. In a next step the CRC is checked.
PACTOR-II is suited to the transfer of large files rather than hand-typed text. The data may be transmitted
as ASCII without compression or can be compressed with HUFFMAN or PSEUDO-MARKOV compression. In
addition, run length encoding (RLE) is included.
Tuning a PACTOR-II Signal
After launching the mode, the first step is to look for a valid PACTOR-II signal in the spectrum: