RTTY Contesting Guide: Software, Tuning and Exchanges

Radioteletype is the oldest digital mode in amateur radio, and in contesting it is very much alive. On a big RTTY contest weekend, the digital portions of the bands fill with the familiar warbling tones of thousands of stations exchanging serial numbers, zones and states at high speed. RTTY contesting combines the keyboard-driven precision of digital modes with the rate and strategy of traditional contests, and many operators who find CW too demanding and phone too noisy discover that it suits them perfectly.

This guide explains how RTTY works, the difference between AFSK and FSK, which decoding software contesters use, how to tune and set up macros, and how to approach your first RTTY contest. Contest rules, exchanges and band segments vary by event and region, so always read the rules of the specific contest and check your band plan before you start.

How RTTY Works

Radioteletype transmits text by switching between two frequencies, called mark and space. Each character is encoded as a short sequence of mark and space bits using the five-bit Baudot code. A receiving decoder listens for the two tones, works out the sequence and prints the characters.

Amateur RTTY contesting almost always uses the same standard settings: 45.45 baud with a 170 Hz shift between mark and space. Because everyone uses the same parameters, any station can tune to any other and start copying immediately, which is exactly what a contest needs.

The mode has no error correction. A burst of noise or a fade corrupts characters, and the decoder simply prints what it thinks it heard. That is why RTTY contest operators repeat key information, use short exchanges and rely on software to suggest likely callsigns.

Mark, space and sideband

By convention, amateur RTTY is transmitted with mark on the higher radio frequency. If your radio has a dedicated RTTY or FSK mode, it handles this automatically. If you generate tones from a sound card and transmit on SSB, the common practice is to use lower sideband so that the tones come out the right way round. Getting this wrong produces a signal that nobody can decode unless they reverse their own settings, so check it before the contest.

AFSK vs FSK

There are two ways to produce an RTTY signal from a modern station, and the choice affects both signal quality and setup complexity. The underlying technique is frequency-shift keying in both cases; what differs is where the shift happens.

• AFSK, audio frequency-shift keying: the computer generates two audio tones and feeds them into the radio’s audio input while the radio transmits in SSB. It needs only a sound card interface, which most digital-mode stations already have.
• FSK, true frequency-shift keying: the computer sends a keying signal to the radio, and the radio itself shifts its transmitted frequency between mark and space. It needs a radio with an FSK input and a keying interface, but it allows the radio’s narrow RTTY filters to be used and avoids problems with audio levels.

Both methods produce good signals when set up correctly. The most important point with AFSK is to keep audio drive low enough that the transmitter does not show ALC action. Overdriven AFSK produces a wide, distorted signal that interferes with neighbours on a crowded contest band. If you already use a sound card for FT8, the same discipline applies; our guide to digital modes beyond FT8 compares RTTY with the other common keyboard modes.

Decoder Software

Most RTTY contesters use a contest logger together with one or more decoding engines. The logger handles the log, the macros and the score; the decoder turns audio into text.

Two decoding engines are especially popular among contesters. MMTTY is a long-established RTTY engine that many loggers can drive directly. 2Tone is a newer decoder written with contesting in mind, and many operators run it alongside MMTTY. Because different decoders behave differently under noise, fading and interference, running two or more at once and comparing their output is a common technique: one decoder may print a callsign correctly when the other produces garbage.

General-purpose digital mode programs such as Fldigi also decode RTTY, and our Fldigi setup guide covers sound card and rig control configuration. For contesting, however, most operators prefer a decoder integrated with their contest logger so that clicking a decoded callsign drops it straight into the entry window.

RTTY Contest Setup Compared

RTTY contest stations range from a single sound card and one decoder to complex setups with several receivers and decoders running at once. The table shows typical levels.

Tuning RTTY Signals

Accurate tuning is essential, because a decoder that is off frequency prints rubbish. Most decoders display a tuning indicator, such as a crossed-ellipse display or a spectrum with markers for mark and space. You tune so that the two tones of the received signal sit on the markers.

In a contest you should not tune by turning the VFO and watching the display every time. Most loggers and decoders let you click on a signal in a spectrum or waterfall display to tune to it, and many have automatic frequency control that follows small drifts. Learn to click accurately on the mark and space tones and let the software do the rest.

Filters help a great deal on a crowded band. A narrow filter centred on your RTTY tones removes adjacent signals that would otherwise confuse the decoder. With FSK, the radio’s RTTY filters are designed for this. With AFSK, make sure your audio tones fall inside the passband of any narrow filter you select.

Macros: The Real Keyboard

In RTTY contesting you rarely type freely. Almost everything is sent from macros, programmed messages triggered by function keys. Well-designed macros keep exchanges short, clear and consistent.

• CQ macro: short and repeated, for example your callsign twice with CQ and the contest name. Long CQs waste time and are more likely to be corrupted.
• Exchange macro: the other station’s callsign, then the exchange, often sent twice for safety. Include a space or line break before and after so the other station’s decoder separates the information cleanly.
• Thank you and QRZ: a short confirmation that ends the QSO and invites the next caller.
• Repeat macros: separate keys for sending only the exchange again, only your callsign, or a request for a repeat.

Keep macros as short as the contest rules and copy conditions allow. Every extra character takes time at 45.45 baud, and over thousands of exchanges those characters add up to many minutes. Our N1MM Logger+ setup guide explains function key configuration for contest loggers in general.

Callsign Accuracy in RTTY

Because RTTY has no error correction, a single corrupted character can turn one callsign into another. Contest loggers help in several ways. They highlight callsigns in the decoded text so you can click them. They compare decoded calls with check partial and call history databases, showing likely matches. And they warn when a decoded exchange looks inconsistent with what is expected for that station. Our guide to Super Check Partial and call history files explains how those databases work.

Use these tools, but think as well. If a decoded callsign looks unusual, ask for a repeat. A few seconds spent confirming a call is much cheaper than a lost QSO and penalty when the log is checked.

Strategy for Your First RTTY Contest

RTTY contests follow the same strategic principles as other contests, with a few twists.

• Start with search and pounce. Tuning across the band and answering CQs lets you learn how exchanges look, how fast stations work and how your decoder copes. Our article on running versus search and pounce explains when to change approach.
• Run when you find a clear frequency. RTTY signals are relatively wide, so a clear frequency is valuable. Once you have one and stations answer, stay and run.
• Space your signal. Leave room between your signal and your neighbours. On crowded bands, stations packed too closely make decoding hard for everyone.
• Watch the whole passband. Many decoders can show several signals at once in the waterfall. While you run, you can spot new multipliers nearby.
• Mind your duty cycle. RTTY is a constant-carrier mode. Many transceivers and amplifiers must be run at reduced power for long RTTY transmissions. Check your equipment’s ratings.

Before the Contest: A Test Checklist

Most first-contest RTTY problems can be found and fixed on an ordinary weekday. Run through this checklist a few days before the event, when there is time to solve anything that does not work.

1. Transmit into a dummy load and monitor the signal. Watch the transmitter’s ALC and power meters while sending a long macro. With AFSK, reduce the audio drive until ALC shows no action and output is steady.
2. Check your polarity on the air. Ask a friend to copy you, or listen to your own signal on a web receiver. If your text appears as garbage while their settings are normal, your mark and space are reversed.
3. Confirm the logger and decoder talk to each other. Clicking a decoded callsign should place it in the entry window, and function keys should key the transmitter and send the right text.
4. Test band changes. Change bands through the logger and confirm the radio, the decoder and the logged band all follow.
5. Configure the contest. Choose the correct contest in the logger so that exchange fields, dupe checking and scoring match the rules.
6. Load fresh databases. Update check partial and call history files for the specific contest if your logger supports them.

Reading the Screen Under Pressure

On a busy band your receive window fills quickly with decoded text, and much of it is fragments of other QSOs, noise and partial callsigns. Experienced RTTY contesters learn to read selectively. They look first for their own callsign, then for the exchange they are waiting for, and ignore the rest. Many loggers colour callsigns differently depending on whether they are new, duplicates or possible multipliers, which speeds this up considerably.

It also helps to clear the receive window regularly, so that old text does not get confused with new replies. A function key or mouse action that clears the window between QSOs is worth setting up. When conditions are poor, slow down: ask for repeats, send your exchange twice and accept a lower rate in return for accurate logging.

The Bottom Line

RTTY contesting uses a simple, standardised two-tone mode at 45.45 baud and 170 Hz shift, which lets any station copy any other immediately. Choose AFSK for simplicity or FSK for the cleanest signal, keep audio drive below ALC, use a contest logger with decoders such as MMTTY and 2Tone, tune by clicking on the mark and space tones, and build short, consistent macros. Confirm doubtful callsigns, respect your equipment’s duty cycle and start with search and pounce before you run. It is one of the most accessible and enjoyable ways into serious contesting.

Frequently Asked Questions

What settings are used for RTTY contesting?

Amateur RTTY contesting almost always uses 45.45 baud with a 170 Hz shift between mark and space, and the Baudot character code. Using the standard settings means any station can tune to any other and copy immediately.

Should I use AFSK or FSK for RTTY?

Both work. AFSK needs only a sound card interface and SSB, but audio drive must be kept low to avoid a wide signal. FSK needs a radio with an FSK input and a keying interface, and lets you use the radio’s narrow RTTY filters.

Which sideband should I use for AFSK RTTY?

The usual practice is lower sideband, so that mark ends up on the higher radio frequency as the amateur convention expects. If your radio has a dedicated RTTY mode, it handles the polarity for you.

What is the best RTTY decoder for contests?

MMTTY and 2Tone are the most widely used decoders among RTTY contesters, often run together. Different decoders cope differently with noise and fading, so running more than one improves copy.

Why are RTTY contest macros so short?

At 45.45 baud every character takes time, and the mode has no error correction. Short, consistent macros send the essential information quickly and reduce the chance that noise corrupts it.

Can my transceiver run full power on RTTY?

Not always. RTTY is a constant-carrier mode, and many transceivers and amplifiers must be run at reduced power for long transmissions. Check the duty cycle ratings in your equipment manuals.