Olivia MFSK and Contestia: Robust Keyboard Modes for Weak Signals

When the band is noisy, the signal fades in and out or the path is disturbed by flutter, many digital modes simply stop decoding. A small group of keyboard-to-keyboard modes was designed to keep going in exactly these conditions, and the best known of them is Olivia MFSK. It trades speed for resilience: the text comes slowly, but it arrives, often when a signal is barely visible on the waterfall. This guide explains how Olivia and its relative Contestia work, what the numbers in a mode name mean, how to choose settings for a given band, how to set up fldigi and how to operate so that you get decodes without wasting bandwidth. It is for operators who already use a mode such as PSK31 or FT8 and want a tool for the difficult days.

What Olivia and Contestia Are

Olivia is a digital mode based on multiple frequency shift keying with strong forward error correction. It sends text by switching among a set of tones, and it spreads each character over many symbols, so that a burst of noise or a short fade destroys only a small part of the information, and the decoder can rebuild the rest. The mode was designed by Pawel Jalocha and is described in the article on Olivia MFSK, where its tolerance of negative signal-to-noise ratios is discussed. Depending on the settings, a decoder can copy signals that are well below the noise level in a normal speech bandwidth.

Contestia is a close relative. It uses a similar structure, but with a smaller set of characters and shorter blocks, which makes it somewhat faster for a given robustness. The Contestia page summarises how it relates to Olivia. A third mode in the same family of robust choices is MT63, which uses many carriers at once and a long interleaver, and is covered in the MT63 article. All of them are keyboard modes: you type, the computer transmits and the other station reads the text on the screen.

Reading the Mode Name

Olivia and Contestia modes are written as two numbers separated by a slash, such as 8/250 or 16/500. The first number is the count of tones, and the second is the bandwidth in hertz. More tones in the same bandwidth mean slower symbols, which makes the mode more robust against timing disturbances such as multipath. A wider bandwidth for the same number of tones means faster symbols and a higher speed, but it also admits more noise. As a rule, a narrow setting with many tones is the choice for the weakest and most disturbed paths, and a wide setting with fewer tones is for stronger signals and faster exchanges.

Common Settings

The table compares the settings you are likely to meet, with some familiar modes for context. Bandwidths are approximate, and the practical result depends on conditions.

Our comparison in digital modes beyond FT8 gives more context on where each of these fits, and the guide to JS8Call describes the more automated approach to weak-signal keyboard messaging.

Setting Up fldigi for Olivia

Most operators use fldigi, because it supports Olivia, Contestia, MT63 and many other modes in one program. If you have not yet configured it, the guide to fldigi setup with sound card, rig control and macros covers the basics. The interface between the computer and the radio must also be sound, with isolation to avoid hum and noise, as described in the article on sound card interfaces and ground loops.

1. Select Olivia from the modes menu, and choose the tone and bandwidth setting, for example 16/500.
2. Set the audio centre frequency, which is usually about 1500 Hz, so that the whole signal sits in the middle of the receiver passband. With a 500 Hz mode, the tones span roughly 1250 to 1750 Hz.
3. Check the receiver filter. If it is narrower than the mode, part of the signal is cut off, so widen it or use the full SSB filter.
4. Look at the Olivia section of the configuration for the synchronisation settings, which control how tolerant the decoder is of frequency error and how long it integrates before it decides.
5. Turn on automatic tracking only if you need it, and use the ALC and audio level rules described below.
6. Enable the mode identification option if you want the other station’s program to switch to your mode automatically.

Keep the Level Low

A robust mode is also a power-hungry one, because it transmits continuously at constant amplitude. That is no reason to run high power. Keep the audio level low enough that the ALC shows no action, and reduce the output power if the transmitter runs hot. The mode works at low power precisely because the decoder is sensitive, and extra power brings splatter without extra copy.

Tuning and Finding Activity

The decoder needs to find your signal to within a small frequency error, and it needs a few seconds to synchronise. Tune a signal so that its tones appear centred in the waterfall, and wait for the first characters. If the text does not appear, check the settings, because a mismatch in tones or bandwidth gives no decode at all. Olivia signals look like a block of closely spaced tones with a distinctive sound, a warbling noise that rises and falls.

Activity is concentrated in the digital segments of the HF bands and around a few well-known frequencies, which change over time and between regions. Look at the band plan for your region, and check a recent source for the current gathering points. Scheduled nets and weekend operating events often use these modes, and a short call on the waterfall frequency usually draws an answer. If you want to know how well you are heard, ask the other station for a report and note the signal-to-noise figure that the program displays.

How to Operate

• Listen first. A mode with a wide signal and long transmissions needs a clear space. Check that the frequency is free for at least a minute.
• Send short messages. A speed of a few words per minute means a long message takes a long time. Keep transmissions compact and keep the exchange simple.
• Use macros. Prepare standard messages with your call sign, name, location and signal report, so that you do not type them slowly while the other side waits.
• Be patient. The decoder has a delay, and the text appears in blocks. Do not interrupt.
• Use the narrowest mode that works. A narrower signal leaves more room for others. Move to a wider setting only if the path demands it.
• Identify clearly. Give your call sign at the beginning and the end and follow the rules of your country.

When to Choose Olivia

Choose Olivia or Contestia when the path is difficult. They are a good choice on low bands with static noise, on paths with flutter such as those that cross the polar region, on crowded bands with weak signals and in emergency or expedition work where an exchange must get through. They are a poor choice when you want speed or when the band is busy and a wide signal will cause problems. For a quick contest exchange, RTTY or a faster mode is better. For automatic scheduled messaging, JS8Call has more tools. For most daytime chat on a clear band, PSK31 or a voice mode is simpler. Treat Olivia as a specialised tool: you need it only occasionally, but when you do, nothing else will do the job as well.

Why the Mode Is So Robust

Three ideas explain the performance. First, the signal is spread over many tones and a long time, so that a fade or a burst of static hits only part of the message. Second, the error correction adds redundancy, so that the receiver can reconstruct missing symbols from the ones that arrive. Third, the receiver correlates the incoming tones against all the possible patterns and chooses the best match, which works even when each individual tone is hard to see. The price of this approach is time: the receiver waits until a whole block has arrived before it decides, so the text appears in bursts, and the speed is low. Once you understand the trade, the settings make sense. A longer block and more tones improve the odds and slow the text, and a shorter block does the opposite.

Using Olivia for Messaging and Emergencies

The robustness makes these modes attractive for emergency and expedition messaging, where a short message must get through on a poor path with simple equipment. A message sent in Olivia can be received on a modest antenna in the presence of noise that would stop a speech contact. Groups that practise emergency communications often keep a robust keyboard mode in their toolbox, together with a link to email over radio, a topic covered in our article on Winlink gateways and modes. Agree the setting, the frequency and the schedule in advance, practise at least once a month and keep the text brief and structured so that the slow speed is not a problem.

A First Test Session

You can learn the mode without a partner. Start fldigi, choose Olivia 16/500 and listen on the digital segment of a band that is open, watching the waterfall for blocks of tones. When you see one, click on it, wait for the first text and note how long the decoder takes to lock. Try the same signal in a different setting and see what happens. When you are ready, find a friend, agree on a setting and exchange a short message. Two or three sessions like this teach the mode better than reading, and they give you confidence to call a station when conditions are poor.

Common Mistakes

• Mismatched settings. If the tones or bandwidth differ between the two stations, there is no decode. Agree the setting before you start.
• Overdriving the audio. A wide signal with distortion splatters across the band.
• Too narrow a receiver filter. The decoder never sees the whole signal.
• Using a wide mode when a narrow one will do. You waste bandwidth and cause interference.
• Not allowing time. The mode synchronises slowly, and you need to wait for the first block.
• Expecting speed. The mode is slow by design, and that is the price of its robustness.

The Bottom Line

Olivia MFSK and Contestia are the tools for the days when other modes fail. They use many tones and strong error correction to decode text far below the noise, at the cost of speed and bandwidth. Choose a setting such as 8/250 for the weakest paths or 16/500 as a general default, centre the signal on the waterfall, keep the audio level low and use short messages and macros. Agree the setting with the other station, listen before you transmit and use the narrowest mode that works. You will not use these modes every day, but when a path is disturbed, they let you keep the conversation going.

Frequently Asked Questions

What is Olivia MFSK?

A keyboard digital mode that uses multiple tones and strong error correction to send text reliably on weak, noisy or fading signals. It is slow but very robust.

What does 16/500 mean in Olivia?

The first number is the count of tones and the second is the bandwidth in hertz. So 16/500 uses 16 tones in a bandwidth of 500 hertz.

What is the difference between Olivia and Contestia?

Contestia is related to Olivia but uses shorter blocks and a smaller set of characters, which makes it somewhat faster for the same robustness.

Which software supports Olivia?

The program fldigi supports Olivia, Contestia and MT63, and other programs also offer them. Both stations need the same tones and bandwidth setting.

Is Olivia better than PSK31?

It depends. Olivia works much better on weak and disturbed signals, but it is slower and wider. PSK31 is more efficient on clear paths.

How much power do I need?

Very little. Low power with a clean signal works well, and extra power can cause splatter. Keep the ALC idle and the audio level low.