PACTOR
PACTOR (English PACket Teleprinting Over Radio ; or Latin for the mediator , modulation type : J2B) is an operating mode for wireless data transmission. The operating mode was specially developed for data traffic on shortwave in order to compensate for the disturbances (fluctuations in field strength, interference) occurring on these frequencies . It is mainly used as a transmission protocol in WinLink , for sending e-mails and files via shortwave. The digital operating mode is used in amateur radio and commercial shortwave services.
The term PACTOR is a made-up word, formed from the expressions Packet Radio and AMTOR .
The developers of PACTOR are the two German radio amateurs Hans-Peter Helfert ( DL6MAA ) and Ulrich Strate ( DF4KV ). The development began in the 1980s as a telecommunications hobby project and later founded a company for further development and sales.
development
The radio amateurs Hans-Peter Helfert ( DL6MAA ) and Ulrich Strate ( DF4KV ) developed the method in the late 1980s as a telecommunications hobby project. Together they founded their own company called SCS in 1992 due to the great acceptance of the new process . SCS offered special hardware and software for PACTOR operation. In the meantime, PACTOR has established itself alongside MIL-STD modems as the global industry standard for global, narrowband data communication via shortwave. In the last 20 years, the technology has changed from a relatively simple method with frequency shift keying (PACTOR-I) to a highly complex system with complex error correction coding and quadrature amplitude modulation with adaptive equalization (PACTOR-4).
The original PACTOR uses bit-synchronous transmission with automatic query in the event of errors such as AMTOR , but with 8 bits per character, significantly longer packets and a cyclic redundancy check as an error detection algorithm.
To carry out the PACTOR operation, special controllers are required that are connected between the terminal (usually a normal PC with a corresponding program) and the transceiver . The latest controller series from SCS has the type designation P4dragon DR-7800 .
With PACTOR-4 a data transfer rate of up to 10 500 bit / s can be achieved with activated compression ; for comparison, ISDN has a data transfer rate of 64,000 bit / s (64 kbit / s).
PACTOR-I
The original PACTOR variant uses AFSK with two tones, like AMTOR at a bit rate of 100 to 200 bit / s.
PACTOR-II
PACTOR-II (PTC-II) uses different modes of the DPSK as modulation method :
| Modulation method |
Symbol rate |
Gross bit rate (bit / s) |
Net bit rate (bit / s) |
|---|---|---|---|
| DBPSK | 1/2 | 200 | 100 |
| DQPSK | 1/2 | 400 | 200 |
| 8-DPSK | 2/3 | 600 | 400 |
| 16-DPSK | 7/8 | 800 | 700 |
When online compression is activated, the bit rate is around 1,200 bit / s.
Bug fix
In order to make the signal more immune to interference, a real convolutional coding is used as a forward error correction . This not only reduces the error rates with a low signal-to-noise ratio, but also with short-term interference pulses and even signal failures, without the corresponding package having to be (actively) requested again. This is important because PACTOR-II supports packets with three times the length, which, due to their size, are correspondingly more susceptible to short disturbances such as Sferics .
compression
To further increase the bit rate, Huffman compression is used at the text level . Alternatively, the “Pseudo Markov Coding” developed by SCS can be used. It increases the data throughput for plain text in comparison to the Huffman codec by a factor of 1.3. During operation, PACTOR-II can check which of the three options (uncompressed / Huffman / Pseudo-Markov) can be transferred the fastest and then uses the respective method for the respective package. The protocol also offers the pseudo-Markov encoder the option of an English and a German coding table. There is also a capital letter mode for Huffman and Pseudo-Markov. There are a total of six different compression options, of which PTC-II selects the best one for each individual packet in real time. In addition, there is a run-length coding , for example for longer underlining in the text or other recurring character strings , which simply transmits the relevant character and its number.
PACTOR-III
In this variant, a PACTOR is low frequency - multi-carrier method with used up to 18 individual carriers (tones) of 400 Hz to 2.4 kHz, each of which PSK is -modulated. Thus, PACTOR-III has the bandwidth of an SSB sideband .
| Level | Number of carriers |
Gross bit rate (bit / s) |
Net bit rate (without compression, bit / s) |
Crest factor (dB) |
|---|---|---|---|---|
| 1 | 2 | 200 | 76.8 | 1.9 |
| 2 | 6th | 600 | 247.5 | 2.6 |
| 3 | 14th | 1400 | 588.8 | 3.1 |
| 4th | 14th | 2800 | 1186.1 | 3.8 |
| 5 | 16 | 3200 | 2039.5 | 5.2 |
| 6th | 18th | 3600 | 2722.1 | 5.7 |
The bit rate depends on the protocol level (see above). Without compression, up to 3600 bit / s are achieved, with compression up to 5200 bit / s. The same procedures are used for compression as with PACTOR-II.
PACTOR-IV
A new modem from SCS was presented at Ham Radio 2011, which manages with poorer signal / noise ratios and can be operated in the new Pactor4 operating mode. This achieves an improvement by a factor of 2 in the transmission speed compared to the PACTOR-III.
modulation
In contrast to PACTOR-II and III, PACTOR-IV only uses a single, phase-modulated carrier (exception: speed level 1). Different variants are used , from simple, spread DQPSK to higher-quality QAM .
| Level | Modulation method |
Gross bit rate (bit / s) |
Net bit rate (bit / s) |
|---|---|---|---|
| 1 | 2-tone DBPSK chirp | 113 | 46.9 |
| 2 | DQPSK, Spread-16 | 225 | 85.32 |
| 3 | DQPSK, Spread-16 | 225 | 147.2 |
| 4th | DQPSK, Spread-8 | 450 | 300.8 |
| 5 | BPSK | 1800 | 433.1 |
| 6th | BPSK | 1800 | 1069.5 |
| 7th | QPSK | 3600 | 2199.5 |
| 8th | PSK8 | 5400 | 3304.5 |
| 9 | QAM16 | 7200 | 4407.5 |
| 10 | QAM32 | 9000 | 5512.5 |
At the highest protocol level, a bit rate of up to 5512 bit / s is achieved without compression, with compression up to 10500 bit / s (with pure text transmission). The same compression methods are used as with PACTOR-II and III.
Web links
- Website of SCS - the inventors of Pactor
- History of the development of Pactor
- Eckart Moltrecht: Chapter from the amateur radio course (callsign DJ4UF)
- Handout for the PACTOR II seminar. (PDF) DARC / OV B 12 and Hersbruck Adult Education Center
- PACTOR for beginners on sy-kaya.de
- For beginners: setting up the Pactor II on a sailing boat. E. Moltrecht DJ4UF website
signal
- Details and audio samples of the Pactor protocol
- PACTOR I in the Signal Identification Wiki (audio files, waterfall graphics and other information).
- PACTOR II in the Signal Identification Wiki (audio files, waterfall graphics and other information).
- PACTOR III in the Signal Identification Wiki (audio files, waterfall graphics and further information).
- PACTOR IV in the Signal Identification Wiki (audio files, waterfall graphics and other information).
Individual evidence
- ↑ Examination questions in the exam sections "Operational Knowledge" and "Regulations" for examinations for the acquisition of amateur radio certificates of classes A and E. (PDF) (No longer available online.) Federal Network Agency for Electricity, Gas, Telecommunications, Post and Railways, October 2006, P. 11 , archived from the original on June 19, 2012 ; accessed on October 24, 2012 (exam question BB407; answer A). Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ^ PACTOR-IV . SCS PACTOR-IV website accessed July 1, 2011
