PACTOR is a frequent visitor in the amateur radio bands. In addition, commercial users also use this system. The data protocol was modified into several variants for this purpose. The WAVECOM software automatically detects and decodes versions 1 to 8.

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. For longer distances, a special longpath mode exits, which has longer breaks between frames and thus allows for distances up to 40,000 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 according 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 necessitates a reduction of the baud rate to 100 Bd.

PACTOR includes HUFFMAN data compression by design. This scheme relies on the fact that frequently occurring 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 uncompressed 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 descriptions.

This mode can also be used to decode connect frames for higher PACTOR levels, as well as frames of the free signal protocol.

Options | CRC Recognition. The detected CRC is displayed in the decoder status bar, see CRC Recognition.

Using Options | CRC Table a certain CRC mask can be defined, see CRC Table.