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Ham radio digital modes explained: the families, and how to tell them apart

There are dozens of digital modes, but only a handful of ways to turn data into sound. Learn the families and most of the names fall into place.

Every digital mode does the same job: it turns text, pictures or voice into sound (or into a radio signal directly) and back again. The differences are in how the sound changes to carry the data, and those differences are exactly what you hear. Here are the families, from simplest to most elaborate.

1. On and off: Morse code

Morse (CW) switches one tone on and off. It's the oldest digital mode and still one of the most popular, because it gets through when little else will and needs almost nothing to send.

2. Two tones: RTTY and friends

RTTY (radioteletype) flips between two tones, one for each binary value. It sounds like a fast, rattling two-note warble. The same idea, with error checking added, is inside NAVTEX marine warnings, DSC distress calls and early PACTOR email links. Packet radio and APRS use two tones too, faster, in the audio range of an FM radio.

3. One tone, shifting phase: PSK

PSK31 keeps one tone and flips its phase, which the ear hears as a soft warble. It is very narrow (31 Hz), so a single band segment can hold dozens of conversations. PSK63 is its faster sibling.

4. Many tones, one at a time: MFSK

Modes such as Olivia, Contestia, MFSK16, THOR and DominoEX step among a set of tones (8 to 32 in the common settings). Each tone carries several bits at once, and strong error correction lets them work through fading and static. They sound like slow, musical tone sequences.

5. Built for the noise floor: the WSJT family

FT8, FT4, WSPR, JT65 and JS8Call are also multi-tone, but they run on a strict clock (15-second slots for FT8) and use powerful error correction, so they decode signals too weak to hear. They trade speed for reach: an FT8 message carries only 13 characters of content. See how to read FT8 messages.

6. Many tones at once

MT63 sends 64 tones simultaneously, and DRM digital broadcasting uses many more (a technique called OFDM, the same idea as Wi-Fi). On a speaker they sound like a dense, flat hiss with sharp edges.

7. Pictures

SSTV (slow-scan TV) turns brightness into pitch, one picture line at a time, with a tick at the start of each line. Weather fax does the same in black and white for maps. Hellschreiber sends text as tiny pictures of letters.

8. Digital voice

DMR, D-STAR, System Fusion (YSF), P25, M17 and FreeDV digitize speech. On an ordinary FM or SSB radio they sound like a harsh buzz or hiss, not a voice; you need a matching decoder to hear the words.

How to tell the families apart by ear

For a longer step-by-step method, see how to identify a radio signal by ear, or browse signals by sound.

Further reading