# PACTOR

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Digital radio modulation mode

**PACTOR** is a [radio modulation mode](https://en.wikipedia.org/wiki/Category:Radio_modulation_modes) used by [amateur radio](/source/Amateur_radio) operators,[1] [marine radio stations](/source/Marine_and_mobile_radio_telephony),[2] military or government users such as the [United States Department of Homeland Security](/source/United_States_Department_of_Homeland_Security) & its cybersecurity agency [CISA](/source/Cybersecurity_and_Infrastructure_Security_Agency),[3][4] and radio stations in isolated areas to send and receive digital information via radio.[5]

PACTOR is an evolution of both [AMTOR](/source/AMTOR) and [packet radio](/source/Packet_radio);[6] its name is a [portmanteau](/source/Portmanteau) of these two technologies' names. PACTOR uses a combination of simple [FSK](/source/Frequency-shift_keying) modulation, and the [ARQ](/source/Automatic_repeat_request) 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](/source/Shortwave_radio) [HF band](/source/High_Frequency) radio, it commonly operates at frequencies between 3 [MHz](/source/MHz) and 30 [MHz](/source/MHz).[8]

## History

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](/source/Bandwidth_(signal_processing)) efficiency of [packet radio](/source/Packet_radio) with the [error-correction](/source/Error-correction) (CRC) and automatic repeat request (ARQ) of [AMTOR](/source/AMTOR).[7] Amateur radio operators were instrumental in developing and implementing these digital modes.[9]

## Current uses

PACTOR radio equipment consists of an HF transceiver, a computer and a [terminal node controller](/source/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](/source/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](/source/ARRL)'s [National Traffic System (NTS)](/source/National_Traffic_System) to pass digital [ARRL Radiograms](/source/ARRL_Radiogram).[11] Newer PACTOR modes are used to transfer large binary data files and Internet e-mail, particularly via the [Winlink](/source/Winlink) global e-mail system.[2][8]

The [SailMail](/source/Sailmail) network transfers e-mail on behalf of marine stations.[12]

## Technical characteristics

PACTOR is a set of standardized modes used by radio operators for FSK [radioteletype](/source/Radioteletype) transfer of digital information over [shortwave](/source/Shortwave_radio) 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](/source/Duplex_(telecommunications)#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](/source/Duplex_(telecommunications)#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)](/source/International_Telecommunication_Union) emission [designators](/source/Types_of_radio_emissions):

- 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]

## Availability and monitoring

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](/source/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]

## See also

- [Shortwave](/source/Shortwave)

- [Radioteletype](/source/Radioteletype)

- [Winmor](/source/Winmor)

## References

1. **[^](#cite_ref-HamStudy_1-0)** Bateman, Richard; Loveridge, Ben (21 April 2025). "3". [*HamStudy Technician License HamBook*](https://hambook.org/tech2022/pt1/chpt3/section-36-digital-and-video-modes/) (2022-2026 ed.). HamStudy. p. 3.6. [ISBN](/source/ISBN_(identifier)) [978-1967466009](https://en.wikipedia.org/wiki/Special:BookSources/978-1967466009). Retrieved 11 April 2026.

1. ^ [***a***](#cite_ref-Marine_radio_2-0) [***b***](#cite_ref-Marine_radio_2-1) [***c***](#cite_ref-Marine_radio_2-2) [***d***](#cite_ref-Marine_radio_2-3) [***e***](#cite_ref-Marine_radio_2-4) [***f***](#cite_ref-Marine_radio_2-5) Corenman, Jim (6 April 2020). ["PACTOR/SSB Installation"](https://sailmail.com/category/installation/). *SnailMail*. Retrieved 11 April 2026.

1. **[^](#cite_ref-3)** ["SHAred RESources (SHARES) High Frequency (HF) Radio Program"](https://www.cisa.gov/resources-tools/programs/shared-resources-shares-high-frequency-hf-radio-program/shares-faqs). *[Cybersecurity and Infrastructure Security Agency](/source/Cybersecurity_and_Infrastructure_Security_Agency)*. [United States Department of Homeland Security](/source/United_States_Department_of_Homeland_Security). Retrieved 11 April 2026.

1. **[^](#cite_ref-4)** Wood, Gary; Chua, Ken. ["SCS Pactor Modems Homeland Security and Emergency Services Organizations Discount Policy"](http://www.felge.us/scsdiscount.pdf) (PDF). *Farallon.us*. Farallon Electronics. Retrieved 11 April 2026.

1. **[^](#cite_ref-5)** ["SCS DR-9400 Review: PACTOR Modem for Reliable Off-Grid & Maritime Communication"](https://hamradiotherapy.com/articles/scs-dr-9400-review/) (Video & Text). *Ham Radio Therapy*. No. Ham radio articles. 7 January 2026. Retrieved 11 April 2026.

1. ^ [***a***](#cite_ref-QEX1991_6-0) [***b***](#cite_ref-QEX1991_6-1) [***c***](#cite_ref-QEX1991_6-2) Helfert, Hans-Peter (October 1991). ["PACTOR—Radioteletype with Memory ARQ and Data Compression"](https://archive.org/details/QEX19812016/QEX%201991/QEX%201991-10/page/n3/mode/2up). *QEX Magazine*: 3–6.

1. ^ [***a***](#cite_ref-ARRL_7-0) [***b***](#cite_ref-ARRL_7-1) [***c***](#cite_ref-ARRL_7-2) [***d***](#cite_ref-ARRL_7-3) ["PACTOR"](https://www.arrl.org/pactor). *ARRL*. The National Association for Amateur Radio. Retrieved 11 April 2026.

1. ^ [***a***](#cite_ref-wimo_8-0) [***b***](#cite_ref-wimo_8-1) [***c***](#cite_ref-wimo_8-2) ["PACTOR: WHEN COMMUNICATION MATTERS, RELIABILITY IS THE ONLY THING THAT COUNTS"](https://www.wimo.com/en/pactor). *WIMO*. WiMo Antennen und Elektronik GmbH, Inc. Retrieved 11 April 2026.

1. **[^](#cite_ref-9)** Anderson, Eric (28 February 2023). ["Amateur Radio Contributions Advance Radio Technology"](https://preppcomm.com/blogs/news/amateur-radio-contributions-advancing-radio-technology?srsltid=AfmBOoqTUItbKNjyPwInz7VJ01cn0a3OcJk2-B8-mSsKZ4lKlBVAGPJA). *Morse Nexus*. PreppComm. Retrieved 11 April 2026.

1. **[^](#cite_ref-10)** ["PTC Plus - The PACTOR Controller"](https://www.p4dragon.com/download/SCS_Manual_PTCplus.pdf) (PDF). *SCS*. 95 SCS GmbH. 1994. pp. 2–3, 5. Retrieved 11 April 2026.

1. **[^](#cite_ref-11)** ["What is the National Traffic System (NTS)?"](https://www.qsl.net/mcarv/What%20is%20the%20National%20Traffic%20System.pdf) (PDF). *ARRL*. American Radio Relay League (ARRL®). Retrieved 11 April 2026.

1. **[^](#cite_ref-12)** ["Sail-mail e-mail service for yachts via Iridium, Inmarsat, or SSB"](http://www.sailmail.com/). *Sail Mail*. Retrieved 1 September 2010.

1. **[^](#cite_ref-WavecomPactor_13-0)** ["PACTOR Packet Teleprinting Over Radio"](http://www.wavecom.ch/content/pdf/advanced_protocol_pactor.pdf) (PDF). *Wavecom*. WAVECOM ELEKTRONIK AG. Retrieved 29 May 2021.

1. ^ [***a***](#cite_ref-SCSP2Proto_14-0) [***b***](#cite_ref-SCSP2Proto_14-1) [*The PACTOR-2 Protocol*](https://www.p4dragon.com/download/PACTOR-2%20Protocol.pdf) (PDF). SCS Spezielle Communications Systeme GmbH.

1. **[^](#cite_ref-SCSADC_15-0)** [*PACTOR-2/3/4 Advanced Data Compression*](https://www.p4dragon.com/download/PACTOR_Advanced_Data_Compression.pdf) (PDF). SCS Spezielle Communications Systeme GmbH.

1. **[^](#cite_ref-16)** Bakare, B.I.; Godwin, J.E. (23 December 2021). ["X-Raying Time Division Duplexing (TDD) in Long Term Evolution (LTE)"](https://www.ajer.org/papers/Vol-10-issue-12/J10125997.pdf) (PDF). *American Journal of Engineering Research*. **10** (12). AJER: 89–97. [ISSN](/source/ISSN_(identifier)) [2320-0847](https://search.worldcat.org/issn/2320-0847). Retrieved 11 April 2026.

1. **[^](#cite_ref-17)** ["More on comparisons of digital HF modes"](http://www.pactor.com/compare.shtml). News. *PACTOR*. Retrieved 1 September 2010.

1. ^ [***a***](#cite_ref-PACTOR_IV_18-0) [***b***](#cite_ref-PACTOR_IV_18-1) ["Technical details on the Pactor-IV protocol"](https://web.archive.org/web/20151023162156/http://www.p4dragon.com/en/PACTOR-4.html). *p4dragon.com*. PACTOR IV. Archived from [the original](http://www.p4dragon.com/en/PACTOR-4.html) on 23 October 2015. Retrieved 25 November 2022.

1. ^ [***a***](#cite_ref-SCSWaveformSummary_19-0) [***b***](#cite_ref-SCSWaveformSummary_19-1) [***c***](#cite_ref-SCSWaveformSummary_19-2) [***d***](#cite_ref-SCSWaveformSummary_19-3) ["Summary on SCS Waveforms"](https://www.scs-ptc.com/download/SCS_Waveforms_Emission_Designators.pdf) (PDF). *SCS*. Spezielle Communications Systeme GmbH & Co. KG. Retrieved 1 June 2021.

1. **[^](#cite_ref-ITU-R_M.1732-2_20-0)** ["Characteristics of systems operating in the amateur and amateur-satellite services for use in sharing studies"](https://www.itu.int/dms_pubrec/itu-r/rec/m/R-REC-M.1732-2-201701-I!!PDF-E.pdf) (PDF). International Telecommunication Union. 2017. ITU-R M.1732-2.

1. **[^](#cite_ref-SCSP3Proto_21-0)** [*The PACTOR-3 Protocol*](https://www.p4dragon.com/download/PACTOR-3%20Protocol.pdf) (PDF). Spezielle Communications Systeme GmbH.

1. **[^](#cite_ref-ITU-R_M.1798-2_22-0)** ["Characteristics of HF radio equipment for the exchange of digital data and electronic mail in the maritime mobile service"](https://www.itu.int/dms_pubrec/itu-r/rec/m/R-REC-M.1798-2-202102-I!!PDF-E.pdf) (PDF). International Telecommunication Union. 2021. ITU-R M.1798-2.

1. **[^](#cite_ref-SCSP4Proto_23-0)** [*The PACTOR-4 Protocol*](https://www.p4dragon.com/download/PACTOR-4%20Protocol.pdf) (PDF). Spezielle Communications Systeme GmbH.

1. **[^](#cite_ref-winlink_24-0)** ["A brief guide to the elements of Winlink 2000"](https://web.archive.org/web/20080512053510/http://www.winlink.org/node/12). *Winlink 2000*. Archived from [the original](http://www.winlink.org/node/12) on 12 May 2008. Retrieved 25 November 2022.

1. **[^](#cite_ref-25)** ["Original request to FCC for Pactor I in Amateur Radio by ARRL"](https://www.fcc.gov/document/amendment-part-97-digital-codes). 1995.

1. **[^](#cite_ref-26)** ["Pactor I open source published in QEX, TAPR, 1994"](https://web.archive.org/web/20151109104848/https://www.tapr.org/kits_an93.html). Archived from [the original](https://www.tapr.org/kits_an93.html) on 9 November 2015. Retrieved 25 November 2022.

1. **[^](#cite_ref-27)** ["Downloads"](https://web.archive.org/web/20180325055429/https://www.scs-ptc.com/de/Downloads.html). *www.scs-ptc.com*. Archived from [the original](https://www.scs-ptc.com/de/Downloads.html) on 25 March 2018. Retrieved 25 November 2022.

1. **[^](#cite_ref-28)** ["PMON"](https://www.scs-ptc.com/pmon.html). *www.scs-ptc.com*. Retrieved 28 November 2024.

1. **[^](#cite_ref-29)** ["Update Info DR7X00 vers. 1.17"](https://web.archive.org/web/20200614235942/https://www.p4dragon.com/en/PMON.html). *p4dragon.com*. Archived from [the original](https://www.p4dragon.com/download/Update_Info_DR7X00_Version_1_17_English.pdf) (PDF) on 14 June 2020. Retrieved 25 November 2022.

- Steve Ford, WB8IMY (2001). "Chapter 5 - PACTOR". *ARRL's HF digital handbook*. Newington, CT: The [American Radio Relay League](/source/American_Radio_Relay_League). [ISBN](/source/ISBN_(identifier)) [0-87259-823-3](https://en.wikipedia.org/wiki/Special:BookSources/0-87259-823-3).{{[cite book](https://en.wikipedia.org/wiki/Template:Cite_book)}}: CS1 maint: numeric names: authors list ([link](https://en.wikipedia.org/wiki/Category:CS1_maint:_numeric_names:_authors_list))

## External links

- ["pactor"](https://web.archive.org/web/20090816151648/http://www.scs-ptc.com/pactor/pactor). *scs-ptc.com*. Archived from [the original](http://www.scs-ptc.com/pactor/pactor) on 16 August 2009.

- ["PACTOR-4"](https://web.archive.org/web/20151023162156/http://www.p4dragon.com/en/PACTOR-4.html). *p4dragon.com*. Archived from [the original](http://www.p4dragon.com/en/PACTOR-4.html) on 23 October 2015.

- ["winlink.org"](http://www.winlink.org/).

- ["airmail2000.com"](http://www.airmail2000.com/).

- ["Pactor-1 Specification"](https://www.qsl.net/kd6pag/usenet/PACTOR.txt).

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Adapted from the Wikipedia article [PACTOR](https://en.wikipedia.org/wiki/PACTOR) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/PACTOR?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.