PACTOR
From Wikipedia, the free encyclopedia
PACTOR is a radio transmission protocol used by amateur radio operators, marine radio stations, and radio stations in isolated areas to send and receive digital information via radio. PACTOR is one of the fastest, most accurate, and most efficient ways to send digital data by radio. A robust network of stations that use PACTOR has been established to relay data by radio to and from the internet, extending internet access to sea based and other isolated users.[1]
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[edit] History
PACTOR (Latin for: The mediator) is a radio modulation mode that uses Frequency Shift Keyed (FSK) modulation. PACTOR developed by Special Communications Systems GmbH (SCS) and released to the public in 1991. PACTOR is an evolution of both AMTOR and packet radio, hence the name PACTOR. It was developed in order to improve the reception of digital data when the received signal was weak or noisy. PACTOR combines the bandwidth efficiency of packet radio with the error-correction (CRC) and automatic repeat request (ARQ) of AMTOR. Amateur radio operators were instrumental in developing and implementing these (new) digital modes. PACTOR is most commonly used on frequencies between 1 MHz and 30 MHz.
[edit] Current Uses
PACTOR has established itself as the new standard for FSK radio teletype on shortwave amateur and marine radio. PACTOR makes it possible to utilize an almost ideal combination of simple FSK modulation and ARQ protocol for robust error detection and data throughput. Generational improvements to PACTOR include PACTOR II and PACTOR III, which are capable of higher speed transmission. These newer versions mostly used by amateur radio operators to transfer large binary data files and to accomplish internet E-mail access over shortwave radio. PACTOR is also used by the sailmail network for e-mail transfer over FCC assigned Marine radio frequencies.[2]
Amateur radio operators and marine operators use the similar equipment to send and receive data (to and from the internet) using the PACTOR digital mode. The equipment consists of an HF transceiver, a computer and a modem that connects between the computer and the transceiver and controls the transceiver. Software running on the computer controls the entire process. The most commonly used program for this purpose is called "Airmail."[3]
This global communications system, called "Winlink" includes base stations located all over the world that accept connections from mobile or fixed stations. The base stations accept e-mail formatted messages and place them on the internet to be delivered as normal e-mail. They also receive and hold e-mails addressed to the mobile stations and forward those messages to them when they make a connection. All Winlink base stations are networked together so the entire operation is coordinated. The mobile (user) stations have no direct access to the internet.
For example, by using PACTOR I and a good connection, this paragraph could be sent in 4 or 5 minutes by radio. Using Pactor II or the even faster PACTOR III, transmission time would be reduced to 1 or 2 minutes.
[edit] Technical Characteristics
HF data transmission by radio amateurs uses medium power (100 watts) over long distances (100 to 4000 km). Such long distances over hostile radio paths require that special attention be paid to the rate at which data is repeated, and error correction. To reduce the amount of data sent, online data compression is utilized, along with a form of error correction called "memory ARQ," in which the last data packet received is held in memory and compared to the next. If BOTH are corrupt, an attempt is made to repair the original packet by combining the two. By combining these open technologies, PACTOR achieves a power efficiency much greater than that of older protocols such as packet, AMTOR, or RTTY. PACTOR has a very narrow waveform and occupies the same bandspace as analog 300 baud packet.
[edit] Criticism of PACTOR
- Cost is an important consideration when choosing PACTOR equipment. PACTOR I is open technology and modems can be purchased in the $50-$150 price range and are in ample supply. The two "enhanced" modes, PACTOR II and PACTOR III, are much faster but have been kept proprietary by the German company, SCS, that developed them. As a result, SCS is the only source for modems capable of these modes. The price of these modems (in some cases as much as a HF radio) discourage many potential users.
- As wireless internet connections, including satellite internet service providers, become commonplace, users are finding that other ways to communicate that are less costly.
- PACTOR transmissions have the potential to disrupt other modes of communication on the same or nearby frequencies. Good operating practices must be followed.
- Due to the closed and proprietary nature of PACTOR II and PACTOR III, there has been some speculation that these modes may be used on shortwave to conceal the nature of the transmission.
[edit] See also
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[edit] Sources referenced
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