Traduction anglaise.   

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 mode: this is the way Multipsk transmits it.

    This mode is included into the software MULTIPSK by Patrick F6CTE, there is the description of this mode and its variants as well as the specifications coming from his software :

Click on the copy of the screen in order to listen to the corresponding audio signal.

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 :
Bandwidth :
600 Hz
Demodulation :
non coherent
Synchronization :
automatic using the signal
Correction code :
Convolution code :
Interleaving :
Pmean/Ppeak :
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).

Note 1:
    the Pactor 1 is only used in HF. It is a public protocol without protection. It seems difficult to program it under Windows because the reaction times are too short and too precise. On the other hand, under DOS, this would be, probably, possible.

Note 2 :
    it exists two other Pactor protocols : Pactor II and III which are more efficients but are not public (it exists a protection of these protocols).

Note 3 :
it exists a FEC version of this mode. The differences are the following:

* there is no acknowlegment protocol, the link is thus not "connected" but "Unproto" type. The exchanges are not free-error (as in ARQ) as the repetitions are not asked in case of error,
* reversely, one or more systematic repetitions of each frame are done, so the term "FEC". As errors are independants, the probability to have several successive errors is very weak, hence if errors are possible in Pactor 1 FEC, they are rare,
* the duration of  the cycles is not fixed but determined by the TX Ham.

Multipsk transmits Pactor 1 FEC frames in the following fixed conditions:

* 100 bauds: to be the most sensitive in HF with a nominal shift of 200 Hz,
* ASCII 8 bauds: to be compatible with all national set of characters and, moreover in Huffman coding, the loss of a frame can lead to lose an indeterminate number of  valid characters,
* a minimum idle time between two frames equal to 0.04 sec (the cycle lasts 1 second): to keep the synchronization which leads of a speed of 40 wpm with one repetition,
* idling is done with the character CHR(21) when nothing must be transmitted: to simplify the exchanges between Hams.

Back to the list of modes included in MULTIPSK