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FT8 (short for Franke-Taylor design, 8-FSK modulation) is a frequency shift keying digital mode of radio communication used by amateur radio operators worldwide. Following release on June 29, 2017, by its creators Joe Taylor, K1JT, and Steve Franke, K9AN, along with the software package WSJT, FT8 was adopted rapidly, becoming the most popular digital mode recorded by automatic spotting networks such as PSK Reporter within 2 years.

Introduction

FT8 is a popular form of digital weak signal communication used primarily by amateur radio operators to communicate on amateur radio bands with a majority of traffic occurring on the HF amateur bands. The mode offers operators the ability to communicate despite unfavorable conditions such as during low solar activity, high RF noise, or with low transmit power. With advances in signal processing technology, software can decode FT8 signals with a signal-to-noise ratio as low as −20 dB in a 2500 Hz bandwidth, which is significantly lower than conventional CW or SSB transmissions.

Operation

FT8 involves 77-bit message blocks transmitted in regular 15-second periods, consisting of 12.64 seconds of transmission time and 2.36 seconds of decode time, giving a digital data rate of 6.09 bits/sec. Source encoding gives an effective message throughput equivalent to about 5 words per minute. The required signal-to-noise ratio in a 2500 Hz bandwidth is −21 dB, so the corresponding E_b/N₀ is 10 log₁₀(2500/6.09) = 26.1 dB greater, or −21 dB + 26.1 = 5.1 dB.

Although FT8 transmissions occur within fixed time windows, the software can cope with discrepancies between sending and receiving systems of up to a second or two. Provided that they are manually set to the correct time every so often (for example, by using WWV or other time standard broadcasters), conventional computer Real Time Clocks are usually adequate. However, most FT8 users take advantage of online time servers using NTP or time signals from the GPS to achieve and maintain better time accuracy, automatically.

Forward error correction helps achieve reliable communication despite common RF issues such as fading and interference, and weak/noisy signals due to marginal propagation paths, low power operation and inefficient antennas (e.g. in restricted and overcrowded urban locations). If anticipated messages are missed or not acknowledged, the software can re-send them in the next time-slot.

The 77 bits are sufficient for free text messages of up to 13 text characters, reminiscent of SMS (TXT) messages or Tweets, while a clever data compression scheme reduces the number of digital bits required to pass structured messages containing conventional callsigns, reports and locators. Long or unusual callsigns are problematic for the protocol, however, despite using hashing to pass condensed representations. Decoding errors and hash collisions occasionally generate false 'callsigns' creating puzzlement or excitement if they appear to be rare but genuine calls.

Applications

There are multiple uses for FT8 including contesting, testing antennas, and for scientific research.

Further information

FT8DMC is a popular club dedicated to this digital mode.

The FT8 Operating Guide gives pragmatic advice on using FT8 for HF communications.

References

1. ^ Burmester, Dale (March 12, 2019). "Amateur Radio Digital Communications Mode FT8" (PDF). Retrieved 2024-11-11.
2. Barron, Robert (2020-02-08). "PSK Reporter". KA5WSS. Archived from the original on 2022-10-06. Retrieved 2022-10-06.
3. Luscre, Anthony (2019-10-11). "FT8—What Is It and How Can I Get Started?". OnAllBands. Archived from the original on 2022-10-01. Retrieved 2022-08-17.
4. "FT8 – Signal Identification Wiki". www.sigidwiki.com. Archived from the original on 2022-08-17. Retrieved 2022-08-17.
5. "FT8 Mode is Latest Bright Shiny Object in Amateur Radio Digital World". www.arrl.org. Archived from the original on 2022-05-28. Retrieved 2022-08-17.
6. "FT8/FT4 from a contester's perspective – VA7ST.ca". Archived from the original on 2022-08-17. Retrieved 2022-08-17.
7. "ARRL Surveying Field Day Participants". www.arrl.org. Archived from the original on 2022-08-17. Retrieved 2022-08-17.
8. "FT8". www.rtl-sdr.com. Archived from the original on 2022-09-30. Retrieved 2022-08-17.
9. Erickson, P.; Liles, W.; Miller, E.; Miller, E. (2020). "Amateur digital mode based remote sensing: FT8 use as a radar signal of opportunity for ionospheric characterization". hamsci.org. Archived from the original on 2022-08-17. Retrieved 2022-08-17.

v t e Amateur radio digital modes
Frequency-shift keying (FSK)	RTTY AMTOR / SITOR PACTOR CLOVER2000 Packet radio (Bell 103 Bell 202) M17
Multiple frequency-shift keying (MFSK)	Olivia MFSK Contestia JT65 FSK441 JT6M WSPR FT8
Phase-shift keying (PSK)	PSK31 PSK63 Q15X25
COFDM	MT63 (based on PSK)
Non-traditional digital modes	Hellschreiber (Feld-Hell) On–off keying Continuous wave Modulated continuous wave Pulse modulation Frequency-hopping spread spectrum (FHSS) Direct-sequence spread spectrum (DSSS) AMPRNet DAPNET

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Culture	History Amateur radio operator Awards DX-pedition Hamfest International operation QSL card Q code Radiosport Vintage amateur radio
Governance	International Amateur Radio Union International Telecommunication Union Frequency allocations ITU prefixes for amateur radio Maritime mobile Licensing
Modes of communication	Voice AM DSB-SC ISB SSB AME FM PM Television ATV SSTV Data/Digital CW ALE AMTOR D-STAR DAPNET EchoLink FT8 Hellschreiber DMT MFSK Packet radio (APRS) PACTOR PSK RTTY Spread spectrum C4FM WIRES-X DMR
Technologies	Amateur radio station Amateur radio software IRLP QRP SDR Satellite Two-way radio Transceivers
Related	Shortwave radio Q code Amateur radio in India

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