Operating Modes Explained: SSB, CW, FT8, and More

Every operating mode is a trade-off between bandwidth, signal-to-noise performance and what the operator has to do. Understanding the trade-off tells you which mode suits which situation far better than a list of features.

SSB — single sideband

Single sideband carries voice by transmitting only one of the two sidebands produced by amplitude modulation, and suppressing the carrier. This halves the bandwidth and concentrates all the transmitted power in the information, which makes SSB roughly four times as efficient as AM for the same intelligibility.

It is the standard voice mode on HF and it requires an operator. You speak, you listen, you take turns. Signal reports are exchanged in the RST system — readability, strength, tone — with the tone figure omitted on voice modes.

CW — Morse code

Continuous wave is the oldest digital mode and still one of the most effective. A keyed carrier occupies only a few hundred hertz, and because the receiver can use a very narrow filter, CW works at signal levels where SSB is unintelligible.

That narrow bandwidth is worth roughly 10 dB over SSB — a considerable advantage on a marginal path. CW also requires no speech processing, no microphone technique and no language in common, which is why it remains the mode of choice for weak-signal and DX work.

FT8 and the weak-signal digital modes

FT8 is a frequency-shift keyed digital mode that transmits for 15 seconds and listens for 15 seconds, using error correction and a very narrow bandwidth. A computer decodes signals far below the noise level that a human ear could detect.

Choosing a mode

For a first contact, SSB is the most forgiving. For working a weak DX station that you can barely hear, CW will get through where SSB will not. For filling a log with confirmations on a quiet band, FT8 is unmatched. For local conversation, FM through a repeater is simplest.

Most operators end up using several modes, chosen by what the band is doing and what they want out of the session.