PACTOR

PACTOR is a radio modulation mode used by amateur radio operators,^[1] marine radio stations,^[2] military or government users such as the United States Department of Homeland Security & its cybersecurity agency CISA,^[3][4] and radio stations in isolated areas to send and receive digital information via radio.^[5]

PACTOR is an evolution of both AMTOR and packet radio;^[6] its name is a portmanteau of these two technologies' names. PACTOR uses a combination of simple FSK modulation, and the ARQ protocol for error detection and data throughput.^[7] Generational improvements to PACTOR include PACTOR II, PACTOR III, and PACTOR IV which are capable of higher speed transmission. As PACTOR was designed to operate as a shortwave HF band radio, it commonly operates at frequencies between 3 MHz and 30 MHz.^[8]

PACTOR (Latin: The mediator) was developed by Special Communications Systems GmbH (SCS) and released to the public in 1991.^[6]

PACTOR was developed in order to improve the reception of digital data when the received signal was weak or noisy.^[6] It combines the bandwidth efficiency of packet radio with the error-correction (CRC) and automatic repeat request (ARQ) of AMTOR.^[7] Amateur radio operators were instrumental in developing and implementing these digital modes.^[9]

PACTOR radio equipment consists of an HF transceiver, a computer and a terminal node controller.^[2] Software running on the computer drives the terminal node controller.^[2][10] The most commonly used amateur program for this purpose is Airmail.^[2][8]

PACTOR is used by Amateur Bulletin board system operators to exchange public messages, and open conversations across the world.^[2] It is also used by the NTSD (digital) portion of the ARRL's National Traffic System (NTS) to pass digital ARRL Radiograms.^[11] Newer PACTOR modes are used to transfer large binary data files and Internet e-mail, particularly via the Winlink global e-mail system.^[2][8]

The SailMail network transfers e-mail on behalf of marine stations.^[12]

PACTOR is a set of standardized modes used by radio operators for FSK radioteletype transfer of digital information over shortwave bands.^[13][7]

Effective radio-frequency communications over long distances over hostile radio paths require that special attention be paid to the rate at which data is repeated and error correction.^[14]

To reduce the amount of data sent, on-line data compression is utilized, along with memory ARQ error correction.^[15]

PACTOR utilizes time-division duplexing for bidirectional, half-duplex communication. To do this, it utilizes 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).^[7][16]

Depending on the version of PACTOR protocol used and the radio-frequency conditions, PACTOR transmission speeds range from 20 to 5200 bits per second (bit/s; net rate) or 9000 bit/s gross rate utilizing speed 10 (32-QAM).^[17][18]

The International Telecommunication Union (ITU) emission designators:

• Pactor I is 340HJ2D or 440HJ2D (at a symbol rate up to 200 symbols per second).^[19]
• Pactor II is 450HJ2D (at a symbol rate of 100 symbols per second).^[19][14][20]
• Pactor III is 2K20J2D (at a symbol rate of 100 symbols per second).^[19][21][22]
• Pactor IV is 2K20J2D or 2K40J2D (at a symbol rate up to 1800 symbols per second).^[19][23][18]

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 auspicies of ARSFI (a Florida-based non-profit organization).^[24]

Pactor modes other than level 1 (P1) are not open source,^[25][26] but are publicly documented^[27] and can be monitored and decoded easily over the air by third parties using free Raspberry Pi software ("PMON for Raspberry Pi")^[28] or PMON utility on the modem itself.^[29]

• Shortwave
• Radioteletype
• Winmor

• "pactor". scs-ptc.com. Archived from the original on 16 August 2009.
• "PACTOR-4". p4dragon.com. Archived from the original on 23 October 2015.
• "winlink.org".
• "airmail2000.com".
• "Pactor-1 Specification".