PACTOR

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.

Technical characteristics

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.

History

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.

Current uses

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).