PACTOR

Pactor (English: Packet Tele Printing Over radio, or in Latin: the mediator, Modulation: J2B ) is a portmanteau formed from the expressions Packet Radio and AMTOR and refers to a digital mode in amateur radio. It was specially developed for the data traffic on shortwave to compensate the occurring at these frequencies disturbances ( fluctuations of the field strength, interference ). It is mainly used as the transmission protocol in WinLink, for sending e- mails and files via shortwave use.

The developers of Pactor are the two German radio amateurs Hans -Peter Helfert (call sign: DL6MAA ) and Ulrich Strate (call sign: DF4KV ). The development began in the 1980s as a communications engineering hobby project. The high acceptance of the new process, the developers have founded in 1992 his own company called SCS, which offers special hardware and software for the Pactor operation. Meanwhile, Pactor has established next to MIL -STD- modem as a global industry standard for global narrowband data communications over short wave. The technology has changed in the last 20 years from a relatively simple procedure with frequency shift keying ( Pactor -I) to a highly complex system with sophisticated error correction coding and quadrature amplitude modulation with adaptive equalization ( Pactor -4).

The original Pactor uses a bit-synchronous transmission with automatic checking with as AMTOR errors, but with 8 bits per character, much longer packets, and a cyclic redundancy check as error detection algorithm.

To carry out the Pactor operation special controllers are needed (usually an ordinary PC with an appropriate program) and the transceivers are connected between the terminal. The latest controller series from SCS has the type designation P4dragon DR- 7800th

With Pactor -4 can be reached up to 10 500 bits / s with compression turned on a data transmission rate; for comparison ISDN has a data transfer rate of 64 000 bit / s ( 64 kbit / s).

• 2.1 modulation
• 2.2 bitrate
• 2.3 Error Correction
• 2.4 compression

• 3.1 modulation
• 3.2 bitrate
• 3.3 compression

• 4.1 modulation
• 4.2 bitrate
• 4.3 compression

Pactor -I

Modulation

The original Pactor variant uses AFSK with two tones such as AMTOR.

Bit rate

100 to 200 bit / s

Pactor II

Modulation

Pactor - II is used as the modulation method different modes of DPSK.

Bit rate

When switched on-line compression, the bit rate is about 1200 bits / s

Error correction

To continue to make the signal interference-resistant, a real convolutional coding is used as forward error correction. This not only reduces the error rates at low signal to noise ratio, but also in short-term disturbance pulses and even dropouts without the appropriate package must be requested again (active). This is important because Pactor II packages supports triple- length, which are correspondingly more vulnerable to short disturbances such as sferics also by their size.

Compression

In order to increase the bit rate on, comes on text layer Huffman compression applied. Alternatively, may be applied, developed by SCS " pseudo Markov encoding ." It increases the data throughput with plain text compared to the Huffman codec by about a factor of 1.3. The PTC -II can check in operation, which was going to transfer the fastest of the three possibilities ( Uncompressed / Huffman / pseudo - Markov ) and applies that method then to the respective package. Furthermore, the Pactor - II protocol provides the pseudo - Markov encoder the possibility of an English and a German coding table. For Huffman and pseudo- Markov, there is also still a capital letter mode. In total there are 6 different compression options, of which the PTC-II chooses each quasi best in real time for each individual package. There is, for example, for a long underlining in text or other recurring strings yet run-length encoding, which simply transfers the sign in question and its number.

Pactor III

Modulation

In this variant, a Pactor low-frequency multi-carrier method with up to 18 individual carriers is (tones) from 400 Hz to 2.4 kHz is used, each of which is single - PSK modulated. Thus Pactor - III has the bandwidth of a SSB sideband.

Bit rate

Depending on the protocol level (see above)

Compression

It will apply the same compression method as with Pactor II.

Pactor -IV

For HAM Radio 2011, a new modem was presented by SCS, which manages with poorer signal / noise ratio and the new mode Pactor4 can be operated. This achieves an improvement by a factor of 2 at the transmission rate in proportion to PACTOR III.

Modulation

Pactor -IV used in contrast to Pactor II and III only a single, phase-modulated carrier ( except Speed ​​Level 1). These come from simple, DQPSK spread to higher-value QAM different variants.

Bit rate

With the highest protocol level

• Without compression up to 5512 bit / s
• With compression up to 10500 bit / s (with plain text transmission )

Compression

It will apply the same compression method as with Pactor II and III.