FT8 vs. FT4: A Comparison of Digital Modes in Amateur Radio

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Amateur radio operators have increasingly turned to digital modes for efficient and reliable communication, particularly in weak-signal conditions. Two of the most widely used digital modes today are FT8 and FT4, both developed by Joe Taylor (K1JT) and the WSJT-X development team. While these modes share similarities, they also have key differences that make them suited for distinct applications. This article explores the technical and operational differences between FT8 and FT4 to help operators choose the best mode for their needs.

What Are FT8 and FT4?

FT8 (Franke-Taylor 8-Frequency Shift Keying) was introduced in 2017 as part of the WSJT-X software. It quickly became popular due to its ability to decode signals at very low signal-to-noise ratios (SNR), enabling contacts in difficult propagation conditions. FT8 is optimized for minimal operator interaction, making it ideal for contesting, DXing, and general QSOs when voice communication is not feasible.

FT4, introduced in 2019, is a faster variant of FT8, designed specifically for contesting and rapid exchanges. It uses a similar transmission structure but reduces the cycle time, allowing for more contacts within a given period. This makes FT4 highly effective for time-sensitive operations such as radio contests.

Technical Differences

Feature	FT8	FT4
Transmission Cycle	15 seconds	7.5 seconds
Bandwidth	50 Hz	90 Hz
T/R Exchange Time	12.64 seconds	5.36 seconds
Decoding Sensitivity	-21 dB	-17 dB
Intended Use	General weak-signal communications, DXing	Contesting, faster QSOs

Transmission Cycle: FT8 operates with 15-second transmission and reception cycles, whereas FT4 reduces this to 7.5 seconds. This allows FT4 to complete more QSOs in a given period.
Bandwidth: FT8 uses a 50 Hz bandwidth, while FT4 has a slightly wider bandwidth of 90 Hz, which allows for quicker transmissions but requires better frequency stability.
T/R Exchange Time: The time needed to complete a full exchange is shorter in FT4, making it ideal for rapid contacts in contests.
Decoding Sensitivity: FT8 is more effective in weak-signal conditions, decoding signals as low as -21 dB, compared to -17 dB for FT4.

Operational Considerations

When to Use FT8:

DXing and weak-signal contacts over long distances.
Low-power (QRP) operations where maximizing sensitivity is crucial.
Casual QSOs where speed is less important.

When to Use FT4:

Contests and fast-paced operating environments.
Situations where a higher QSO rate is required.
Moderate signal conditions where a slight reduction in decoding sensitivity is acceptable.

Pros and Cons

Mode	Pros	Cons
FT8	Excellent weak-signal performance, ideal for DXing and low-power ops	Slower cycle time, fewer QSOs per hour
FT4	Faster QSOs, better for contests and events	Slightly lower sensitivity, requires more stable conditions

Conclusion

Both FT8 and FT4 have their advantages, depending on the operator’s goals. FT8 is the preferred choice for weak-signal work and long-distance communication, while FT4 is the go-to mode for contesting and high-speed operations. Understanding these differences allows amateur radio enthusiasts to select the most effective digital mode for their specific needs.

For operators looking to experiment, both modes are supported by WSJT-X, and switching between them is straightforward. Whether chasing DX or maximizing contest scores, these digital modes continue to play a crucial role in modern amateur radio communication.