What is PACTOR?
PACTOR (or now called PACTOR I) arose to cover the shortcomings of PACKET and AMTOR. It behaves very well in fading and noise environments, which is why it is mainly used on HF. It has now been superseded by the more advanced PACTOR II and PACTOR III, but is still in use.
PACTOR-I is used by many groups including Sailmail for sailors to send and receive emails. It is also used by radio amateurs, government and diplomatic agencies and even NGOs. PACTOR-I is also used as a Selcall protocol to establish connections with other PACTOR modems. All PACTOR-II, III and IV modems use PACTOR-I for calling.
PACTOR I has a rate of 200 Bd, Huffman compression technique, uses 2 FSK tones with 200 Hz offset and true binary data transfer capability. Created by Ulrich Strate (DF4KV) and Hans-Peter Helfert (DL6MAA) in 1990.
PACTOR II is an advanced variant in which the exchange rate reaches 800 bit/s.
It is up to 8 times faster than PACTOR I. PACTOR II has a frequency bandwidth of 450Hz. This is a proprietary standard developed by SCS GmbH & Co. KG, Hanau, Germany.
Uses 2 DPSK tones. PACTOR I SELCALL is used when establishing an initial connection between the two operators.
PACTOR III is a software upgrade using the same modems, where the speed reaches 2722 bit/s.
PACTOR III introduces 6 speed levels that provide higher performance and improved durability compared to PACTOR I and II. PACTOR III is on average 3.5 times faster than PACTOR II. Under optimal conditions, PACTOR III becomes over 5 times faster.
The PACTOR III has a maximum frequency bandwidth of 2400 Hz. This is a proprietary standard developed by SCS GmbH & Co. KG, Hanau, Germany.
The PACTOR III has 6 speed modes made up of 2, 6, 14, 16 and 18 tone modulations with each tone spaced at 120Hz.
During a standard transmission link between two operators, PACTOR III modems will transmit a PACTOR I SELCALL to determine the optimal mode and speed for establishment between the two operators.
PACTOR IV is the latest iteration of the PACTOR series, progressing from PACTOR I-III. It is 1.5x-3x faster than PACTOR III and has 10 speed levels.
It is also a patented standard developed by SCS GmbH & Co. KG, Hanau, Germany.
This mode is used exclusively in the P4dragon series of SCS shortwave data modems. All P4dragon series modems are backward compatible with PACTOR I-III and, like PACTOR II and III, use PACTOR I SELCALL to establish connections with other modems.
More information about these and other digital regimes can be found for example at: http://www.arrl.org/FandES/field/regulations/techchar/