FT8 gets all the attention these days, but it’s not actually the most robust digital text mode available to you. Olivia and MFSK were built for a different problem: pulling a readable message out of conditions bad enough to wipe out almost anything else, at the cost of being considerably slower.
How Olivia gets its resilience
Olivia spreads each character across multiple tones using MFSK (multiple frequency-shift keying) combined with heavy forward error correction, which lets it reconstruct a message even when large portions of the transmission are lost to noise or fading. Common configurations use 8 or 16 tones across bandwidths from 250 Hz to 1000 Hz, and you’ll see notation like Olivia 8/250 or Olivia 16/500 describing the tone count and bandwidth combination in use.
The tradeoff: speed
That resilience comes at a real cost. Olivia and other MFSK modes are noticeably slower than PSK31 or RTTY, let alone FT8, which is fine for the situations they’re actually built for: long-haul contacts on marginal HF paths, disaster and emergency traffic where getting the message through matters more than getting it through fast, and generally any circuit where reliability trumps throughput.
Where these modes actually get used
You’ll mostly find Olivia and MFSK activity clustered in dedicated segments on 20, 30, and 40 meters, and among operators specifically interested in weak-signal digital work rather than general ragchewing. Software like Fldigi supports both modes natively, so if you already run Fldigi for RTTY or PSK31, trying Olivia costs you nothing but a mode change in the same software. It’s a good mode to have in reserve for the nights when nothing else seems to be getting through.
Related reading: What Is SSTV? · NBEMS and Practice Nets · JTDX vs WSJT-X