PACTOR 1 is an AFSK mode using an ARQ protocol (as AMTOR ARQ. It allows QSO error free in HF. It can be also used as a FEC which MultiPSK software can do.
Creators : Ulrich Strate (DF4KV) and Hans-Peter Helfert (DL6MAA) in 1990
Description :
Baud rate : 100 or 200 (200 bauds initially) automatically selected according of the propagation conditions
Speed : between 0 and about 260 mpm according to the number of repetitions, the propagation conditions and the selection or not of a compressed mode (Huffman),
Modulation : FSK two tones (« mark » and « space ») with a shift between tones of 200 Hz
Polarities are reversed for each new information frame.
Reception mode : indifferent (LSB or USB)
Character set : ASCII characters + ANSI extended characters in "8 bits" or only ASCII characters with an Huffman compression
Shape of pulse : rectangular
Bandwidth : 600 Hz
Demodulation : non coherent
Synchronization : automatic using the signal
Correction code : no
Convolution code : no
Interleaving : no
Pmean/Ppeak : 1
Lowest S/N at 100 bauds : about -4 dB
Pactor 1 protocol (principle): all the communication is done through "frames" (limited set of characters) and control signals (CS1 to CS2) as in AMTOR ARQ. There are two different sorts of frames: one to synchronize, when starting, for the connection and the information frames which allow the communication through an automatic procedure of transfer and anknowlegment by the signals CS1 to CS4. Each information frame is composed of:
* a header (a special character),
* an information field where data is located (8 bytes at 100 bauds and 20 at 200 bauds),
* a FCS field composed of 2 bytes where is located the CRC ("Cyclic Redundancy Check Sum") calculation on all the frame data until this field (except header). A difference between calculated CRC and received CRC makes the frame invalid.
It is an ARQ mode because each frame, bad or good, receive an acknowlegment, positive or negative, followed by an immediate repetition if the frame has been bad received. The duration of each cycle is fixed (1.25 sec).
