PACTOR
A digital mode combining AMTOR and packet radio for HF data transfer.
PACTOR is a digital radio modulation mode used to send and receive information over the air. It is utilized by amateur radio operators, marine stations, government and military users—including the U.S. Department of Homeland Security and its cybersecurity arm CISA—and radio stations in remote areas. The name is a blend of AMTOR and packet radio, the two technologies it evolved from. PACTOR combines simple FSK modulation with the ARQ protocol for error detection and data throughput. Successive versions—PACTOR II, III, and IV—offer higher transmission speeds. Designed for shortwave HF bands, it typically operates between 3 MHz and 30 MHz.
Developed by Special Communications Systems GmbH (SCS), PACTOR was released publicly in 1991. Its name comes from Latin, meaning "the mediator." It was created to improve digital data reception under weak or noisy signal conditions, merging packet radio’s bandwidth efficiency with AMTOR’s CRC error correction and automatic repeat request (ARQ). Amateur radio operators played a key role in developing and implementing these digital modes.
A PACTOR station consists of an HF transceiver, a computer, and a terminal node controller, with software—most commonly Airmail—driving the controller. Amateur bulletin board system operators use it to exchange public messages and hold conversations worldwide. It also supports the digital portion of the ARRL’s National Traffic System (NTS) for passing ARRL Radiograms. Newer PACTOR modes handle large binary files and internet email, especially through the Winlink global email system. The SailMail network uses it to transfer email for marine stations.
PACTOR is a set of standardized modes for FSK radioteletype digital data transfer over shortwave bands. Effective long-distance communication over difficult radio paths requires careful attention to data repetition and error correction. Online data compression and memory ARQ error correction reduce the amount of data sent. It uses time-division duplexing for bidirectional half-duplex communication on a single frequency, alternating transmission in cycles of about 1.25 to 1.4 seconds, rather than using separate frequencies for send and receive. Depending on the protocol version and radio conditions, transmission speeds range from 20 to 5200 bits per second (net rate), with a gross rate of up to 9000 bit/s using speed 10 (32-QAM).
- Developed by
- Special Communications Systems GmbH (SCS)
- Released to public
- 1991
- Frequency range
- 3 MHz to 30 MHz
- Transmission speeds
- 20 to 5200 bit/s (net rate) or 9000 bit/s gross rate utilizing speed 10 (32-QAM)
- Pactor i symbol rate
- up to 200 symbols per second
- Pactor ii symbol rate
- 100 symbols per second
- Pactor iii symbol rate
- 100 symbols per second
- Pactor iv symbol rate
- up to 1800 symbols per second
Lore & Background
PACTOR (Latin: The mediator) was developed by Special Communications Systems GmbH (SCS) and released to the public in 1991. It was developed in order to improve the reception of digital data when the received signal was weak or noisy. It 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 digital modes.
PACTOR utilizes time-division duplexing for bidirectional, half-duplex communication. To do this, it uses a single frequency to send and receive data by alternating transmission time, usually with 1.25 to 1.4-second cycles; this is opposed to using separate frequencies for sending and receiving data (frequency-division duplexing). To reduce the amount of data sent, on-line data compression is utilized, along with memory ARQ error correction.
PACTOR radio equipment consists of an HF transceiver, a computer and a terminal node controller. Software running on the computer drives the terminal node controller. The most commonly used amateur program for this purpose is Airmail.
Reader's Guide
PACTOR is significant as a standardized set of modes for FSK radioteletype transfer of digital information over shortwave bands, enabling effective long-distance communication over hostile radio paths. Its design pays special attention to the rate at which data is repeated and error correction. The mode is used by Amateur Bulletin board system operators to exchange public messages and open conversations across the world. It is also used by the NTSD (digital) portion of the ARRL's National Traffic System (NTS) to pass digital ARRL Radiograms. Newer PACTOR modes are used to transfer large binary data files and Internet e-mail, particularly via the Winlink global e-mail system. The SailMail network transfers e-mail on behalf of marine stations. A robust network of PACTOR stations has been established to transfer data between radio stations and the Internet, extending Internet access to sea-based and other isolated users, led by volunteers involved with Winlink, under the auspices of ARSFI (a Florida-based non-profit organization). PACTOR modes other than level 1 (P1) are not open source, but are publicly documented and can be monitored and decoded easily over the air by third parties using free Raspberry Pi software ("PMON for Raspberry Pi") or the PMON utility on the modem itself.
Did You Know?
- PACTOR is a portmanteau of AMTOR and packet radio.
- PACTOR IV can achieve a gross rate of 9000 bit/s using speed 10 (32-QAM).
- The most commonly used amateur program for PACTOR is Airmail.
More in Radio Modulation Modes, Part 2 1-24
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