13 December 2014

PACTOR-IV ARQ ("Dragon" modem)

PACTOR-IV ARQ ("Dragon" modem)
This is a proprietary standard developed by SCS GmbH & Co. KG, Hanau, Germany. This mode is used exclusively in SCS's P4dragon series of shortwave data modems, from here the nick name "Dragon". The P4dragon series modems are all backwards compatable with PACTOR I-III, and, like PACTOR II and III, uses PACTOR I SELCALL to establish connections with other modems.

This PACTOR-IV transmission was heard 13 Dec 14 on 16680.0 KHz/USB.

PACTOR-IV has very adaptive 10 speed levels (waveforms):
SL    Modulation   
1    - 2 Tone Chirp   
2    - DQPSK, Spread-16
3    - DQPSK, Spread-16    
4    - DQPSK, Spread-8   
5    - BPSK   
6    - BPSK   
7    - QPSK
8    - PSK-8
9    - QAM-16   
10  - QAM-32

Spread-16 and Spread-8 relates to the spreading factor of the modulation. It consists of modulation with 8 times or 16 times frequency spreading.  
Below the DQPSK spread-16 modulation 112.5 Baud in the two busrts signed as a and b in the sonogram:

At the lowest speed level, PACTOR-4 uses a newly developed 2-tone chirp modem. The chirp mode is robust against narrow band and part-channel interference, as well as against selective fading.

- the signal occupies more than 2000 Hz, with pilot tone at 3250 Hz (center frequency 1500 Hz)
- two "sweep" tones 1000 Hz spaced, rising time: 3,5 seconds from 500 and 1500 Hz to 1500 and 2500 Hz

Below the measurements of frequencies and times of the two sweep tone:

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