What is the bandwidth of an FT8 signal?

FT8 uses 8-FSK (Frequency Shift Keying) modulation, meaning it shifts between 8 distinct tones to transmit data. The tones in an FT8 signal are spaced exactly 6.25 Hz apart. To calculate the total bandwidth, you multiply the 8 tones by the 6.25 Hz tone spacing, which results in exactly 50 Hz. This extremely narrow bandwidth is a key reason FT8 is so efficient and robust for weak-signal propagation, allowing signals to be decoded even when buried in noise. The 2.4 kHz option is a distractor that refers to the typical bandwidth of a standard SSB voice channel. While amateur operators usually open their radio's filter to 2.4 kHz or 3 kHz to monitor dozens of FT8 signals simultaneously within that audio passband, a single FT8 signal only occupies 50 Hz.