Wavecom W61PC V7.5.0 - Manual (Page 202)

192  Transmission Modes WAVECOM Decoder W61PC/LAN Manual V7.5
Parameter Value
Operation modes Simplex ARQ
Modulation FSK
Symbol rate 100.0 and 200.0 Bd adaptive
Receiver settings DATA, CW, LSB or USB
Input format(s) AF, IF
Additional Info ITA-5 with block coding
PACTOR operates as a bit synchronous simplex system in a fixed timing cycle. The entire cycle length is
1.25 seconds and the packet length 0.96 seconds. Consequently the correlation amounts to 250 bits at
200 Baud. The change-over time and signal propagation delay limits the system’s range to approximately
20.000 km.
The PACTOR data block consists of three sections: Header, data and control (status and 16 bit CRC). At
100 Baud the data field is 64 bits and at 200 Baud it increases to 160 bits. Block coding is performed ac-
cording to the CCITT standard starting with the data section.
PACTOR operates adaptively so the baud rate can be either 100 or 200 Baud. During day time 200 Baud
may be successfully used. In the evening, however, strong propagation distortion occurs which necessi-
tates a reduction of the baud rate to 100 Bd.
PACTOR includes HUFFMAN data compression by design. This scheme relies on the fact that frequently oc-
curring characters e.g. space, e, n or i, can be represented with shorter bit combinations than characters
which are rarely used. A compression factor of approximately 1.7 is achieved in comparison to uncom-
pressed ASCII.
Looking purely at monitoring, the Huffman code has the disadvantage that compression synchronization
may be lost during propagation disturbances and so the remaining text in the data block is also lost.
Detailed descriptions of the PACTOR protocols can be obtained in the radio amateur literature. It must
however be pointed out that real-world PACTOR implementations differs considerably from these descrip-
tions.
Options | CRC Recognition. The detected CRC is displayed in the decoder status bar, see “ CRC Recogni-
tion ” on page 30.
Using Options | CRC Table a certain CRC mask can be defined, see “ CRC Table ” on page 31.
PACTOR-FEC
PACTOR-FEC is a bit synchronous simplex system and is based on PACTOR.
Parameter Value
Frequency range HF
Operation modes Broacast, FEC
Modulation FSK
Symbol rate 100 and 200 Bd
Shift 200 Hz
Receiver settings DATA, CW, LSB or USB
Input format(s) AF, IF
Additional Info ITA-5 with block coding
The PACTOR-FEC data block consists of three sections: Header, data and control (status and 16 bit CRC).
At 100 Bd the data field is 64 bits and at 200 Bd it increases to 160 bits. Block coding is performed ac-
cording to the CCITT standard starting with the data section.