21 December 2014


PACTOR-III is an adaptive transmission mode that provides higher throughput and improved robustness compared to PACTOR-I and –II, both designed for operation within a bandwidth of 500 Hz. To achieve the improved features, PACTOR-III uses up to a maximum of 18 tones spaced 120 Hz, thus occupying a maxmum bandwidth of 2160 Hz.

System: PSK, Half-duplex synchronous ARQ
Speed: 100.0 Baud
Modulation: DBPSK, DQPSK; 2, 6, 14, 16, or 18 tones (see the notes about the Differential PSK at the end of the post)

PACTOR-III two tones sonagram
PACTOR-III two tones spectrum

Six so-called Speed Levels (SL) are specified, which are predefined combinations of modulation type (B = DBPSK or Q = DQPSK), channel coding and number of tones (2, 6, 14, 16, or 18) as well as positions of tones

For all Speed Levels, the modulation rate of each tone is 100 Baud.

As propagation conditions change, PACTOR-III is able to select the most suitable speed level. Under very poor conditions it changes to speed level 1, whereas, under optimum conditions, speed level 6 is used. As in the PACTOR standards, the frame durations are 1.25 seconds (short cycle) and 3.75 seconds (long cycle for data mode). A long path option is available to enable contacts up to 40.000 km. In such a case, the duration of the short and long cycle is extended to 1.4 and 4.2 seconds, respectively.

Initial link establishment is achieved using the frequency shift-keying (FSK) protocol of PACTOR-I, corresonding to the lowest protocol level. If both calling and called stations are capable of PACTOR-III, automatic switching to this protocol is done.
For data transmission, which is robust against all kinds of disturbances, a decision must be made, whether a short or a long frame-length should be used.
(source:Wavecom manual)
Below an example from a my reception of OSY Pactor-III transmission: note the Speed Level (SL1) and the lenght of the frame (LONG) used:

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