The science behind the remarkable efficiency of FT8

FT8 (Franke-Taylor 8-FSK modulation), a digital mode developed for amateur radio, has become incredibly popular since it's introduction in 2017, especially for making contacts in challenging conditions. This mode is particularly effective at low power levels and with weak signals, making it a favorite among hams who enjoy the thrill of long-distance communication with minimal equipment. But why does FT8 perform so well under these circumstances? Here are some key reasons.

Efficient Signal Encoding

FT8 uses a highly efficient encoding method that packs a lot of information into a small bandwidth. This means the mode can transmit data effectively even when the signal is weak or the conditions are poor. The encoding is designed to be robust against interference and noise, which are common on HF bands, especially at low power levels.

Short Transmission Time

Each FT8 transmission lasts only about 15 seconds. This short duration reduces the chance that the signal will be affected by sudden changes in the ionosphere or local interference. With these quick exchanges, FT8 can take advantage of brief openings in the band conditions, allowing successful contacts that might be missed with longer transmissions.

Error Correction

FT8 includes strong error correction algorithms. These algorithms can identify and fix errors in the received signal, ensuring that the message (and particularly the callsign within the message) can still be understood even if parts of it are lost or corrupted. This is crucial for weak signal work, where parts of the transmission might be affected by noise or fading.

Low Bandwidth

FT8 signals occupy very little bandwidth (only about 50 Hz). This narrow bandwidth means that FT8 can fit into crowded HF bands without causing or suffering from much interference. It also means that more of the transmitter's power is concentrated into a smaller space, making the signal stronger relative to the background noise.

Many FT8 narrowband signals spread across a 1200Hz band segment

Synchronisation

FT8 requires precise time synchronisation between transmitting and receiving stations, typically achieved using internet time servers. This synchronisation ensures that both stations are listening and transmitting at the exact same time, making it easier to decode weak signals because the timing is predictable.

In summary:

FT8 excels at low power and weak signal levels due to its efficient encoding, short transmission times, strong error correction, narrow bandwidth, precise synchronisation, and user-friendly software. These features work together to make FT8 a powerful tool for amateur radio operators, enabling reliable communication even in challenging conditions. 

Whether you're trying to reach a distant station or simply want to make contacts with minimal power, FT8 offers a robust solution that maximises the potential of weak signals. Add to that the popularity of this mode and number of active stations at any given time, your chances of making contacts are very high. 

I myself was amazed when I first started to use FT8 at the amount of DX in the FT8 band segments and work several new countries within my first couple of weeks using the mode with only 10w output into a 1/4 wave vertical antenna.