What Is RTTY? An Introduction to Radio Teletype
RTTY is a way for amateur radio operators to send text messages over radio waves. The abbreviation stands for Radio Teletype, and the concept is elegantly simple: text is converted into digital signals and transmitted over HF radio frequencies, where it can be decoded and displayed at the receiving station. Unlike voice transmissions or Morse code, RTTY sends typed messages in a way that can be decoded by specialized equipment or software, making it a fascinating bridge between traditional and digital communication.
The History of RTTY and Its Origins in Commercial Telegraphy
RTTY (RadioTeleTYpe) is the oldest digital mode in amateur radio, with roots in the mechanical teletype machines of the 1950s. Its commercial origins go back even further. RTTY traces its origins back to the beginning of landline teleprinter operations in 1849. The US military used radioteletype in the 1930s, expanding usage during World War II. When military and commercial operators began decommissioning their mechanical teleprinters in the latter half of the twentieth century, surplus machines found their way into amateur radio shacks, and hams quickly embraced the mode for HF communication. The military and businesses first used it. Later, hams adopted it for contests, long-distance chats, and emergency communication.
How RTTY Differs from Other Digital Modes Like PSK31 and FT8
Understanding RTTY's place in the digital mode ecosystem requires a brief comparison. RTTY relies on a simple two-tone frequency shift keying, while FT8 depends on structured, time-synchronized messages. Where FT8 and similar WSJT-X modes operate on rigid timed sequences and highly structured, automated exchanges, RTTY is a free-flowing, real-time, keyboard-to-keyboard mode. The contents of FT8 messages are very limited; there are only half a dozen stereotyped message formats. The full range of contest exchanges seen in CW, SSB, and RTTY contests cannot be supported by WSJT-X and similar programs.
RTTY uses FSK (frequency shift keying) and is 170 Hz wide. PSK31 uses phase shift keying and is only 31 Hz wide. PSK31 works better in very noisy conditions due to its narrow bandwidth. RTTY has a larger presence in contest operating and has been around much longer.
Why RTTY Remains Popular in Amateur Radio Today
RTTY remains active and relevant today — it is a major mode in contest operating, with dedicated RTTY contests like CQ WW RTTY and BARTG attracting thousands of entries worldwide. The numbers back this up: in the 2024 RTTY Roundup, there were 1,953 logs submitted — 160 more than in 2023. RTTY is a classic digital mode that remains popular among amateur radio operators for its robust performance, especially during contests and DX operations. Hams use RTTY to exchange text messages, often at speeds of 45 or 75 baud, making it a reliable choice for QSOs even when propagation is challenging. It is a mode that combines historical significance with modern software tools, attracting operators who enjoy both the technical challenge and the unique sound of its shifting tones.
How RTTY Works: The Technical Foundation
Frequency Shift Keying (FSK) Explained
RTTY uses Frequency Shift Keying — the carrier frequency shifts between two tones (Mark and Space) to represent binary data. Think of it as a sophisticated on/off switch operating at radio frequencies. The transmitter alternates between two precise audio tones — when a "Mark" is sent, the carrier sits at one frequency; when a "Space" is sent, it shifts to another. The receiving station's decoder monitors these shifts and reassembles the original text characters. This is why RTTY produces that distinctive warbling sound so familiar to HF operators scanning across digital sub-bands.
Understanding Baudot Code and the 5-Bit Character Set
RTTY uses the Baudot character set — a 5-bit code that predates ASCII. Because 5 bits allow only 32 characters, Baudot uses two shift states: Letters (LTRS) and Figures (FIGS). The receiver switches between states when it receives a shift character. This gives access to letters, numbers, and a limited set of punctuation. The limited character set means RTTY exchanges are brief and standardised — you will not see lowercase letters, complex punctuation, or extended characters in RTTY. This limitation is, counterintuitively, part of RTTY's charm and efficiency in contest environments, where brief, unambiguous exchanges are prized above all else.
AFSK vs FSK: Which Method Should You Use?
Two methods exist for generating and transmitting RTTY signals: Audio Frequency Shift Keying (AFSK) and direct Frequency Shift Keying (FSK). AFSK is when you send audio from a TNC or Sound Card to the audio input of your transmitter either via the mic input or accessory jack. FSK is when you send on/off keying from a TNC or Serial COM port to the FSK input of your transmitter.
Most modern transceivers today have an FSK input. By using the FSK input to your transceiver, you can then operate the radio in the RTTY or FSK position and make use of filters available for receiving RTTY, such as a narrow 250 Hz or 500 Hz IF filter. For newcomers, AFSK is generally easier to configure since it requires only an audio connection and no additional serial port hardware. For serious contest operators, FSK is preferred because this is actually cleaner than AFSK through the audio path and is preferred by serious RTTY contesters.
Baud Rate and Shift: Standard RTTY Parameters
The standard amateur RTTY shift is 170 Hz, with Mark at 2125 Hz and Space at 2295 Hz (when using AFSK through a sound card). At 45.45 baud, RTTY is slow by modern standards but robust — it has been reliably decoded under challenging band conditions for decades. This is called the "shift" and is commonly 170 Hz in almost all amateur RTTY today. The higher frequency RF carrier is called "Mark" and the lower one is called "Space." The Mark and Space are often referred to as "tones" because they are two audio tones in the headphones.
RTTY Equipment: What You Need to Get Started
Getting on RTTY in 2026 requires less specialized hardware than ever before. While once requiring dedicated hardware teleprinters, modern RTTY operation is almost entirely software-driven, using computer sound cards to encode and decode signals. Here is what you need:
Transceivers with Built-In RTTY Support
Most modern HF transceivers include a dedicated RTTY or FSK mode, making setup straightforward. Popular choices include the Icom IC-7300, IC-7610, Kenwood TS-590SG, Yaesu FT-991A, and FLEX-6000 series SDRs. Key components include a transceiver capable of transmitting and receiving on HF or VHF bands. When shopping for a transceiver specifically for RTTY, look for a built-in FSK keying input, RTTY-specific narrow IF filters (250–500 Hz), and a data port that provides both audio and PTT control via a single USB cable.
External TNC (Terminal Node Controller) Options
A TNC — Terminal Node Controller — is a hardware device that sits between your radio and computer, handling digital encoding and decoding tasks. A terminal node controller (TNC) or sound card interface is needed for digital signal processing. While TNCs were essential in the early days of RTTY, they have largely been replaced by software-based soundcard solutions. However, dedicated hardware TNCs still offer advantages in certain situations, particularly for operators who need reliable FSK keying without a computer serial port or for multi-mode digital operation.
Soundcard Interfaces and Popular Models
The soundcard interface is the bridge between your radio and your computer. It routes receive audio from the radio to your computer's sound input, routes transmitted audio from the computer to the radio's microphone or data port, and provides PTT (Push-To-Talk) control. Popular commercial interfaces include the Tigertronics SignaLink USB, RigBlaster series, and the micro:KEYER from microHAM. These units provide electrical isolation between your radio and computer, dramatically reducing the risk of ground loops and RF feedback — two of the most common problems in digital mode stations.
Recommended Computers and Software for RTTY Operation
Any modern Windows, macOS, or Linux computer is capable of running RTTY software. Windows remains the most common platform due to the wider availability of RTTY software, particularly for contesting. A basic dual-core processor with 4GB of RAM is more than adequate. The PC's internal soundcard is fully adequate for RTTY. However, a dedicated external USB soundcard interface is recommended over the internal soundcard for better isolation and noise performance.
Best RTTY Software for Amateur Radio
MMTTY: The Gold Standard for RTTY Decoding
MMTTY, developed by JE3HHT, utilizes a soundcard for RTTY decoding and encoding, with support for external FSK keying via parallel or serial ports, including USB serial adapters. Since 2000, when the freeware MMTTY was introduced by JE3HHT, almost all decoding (and encoding for transmission) has been done in software on a PC. MMTTY's combination of accuracy, speed, and ease of configuration has made it the default choice for RTTY contesting worldwide. MMTTY integrates with COMFSK and EXTFSK/EXTFSK64 for precise FSK keying, enabling direct radio control. For newcomers, MMTTY is available as a standalone application; for contesters, it integrates tightly with N1MM Logger+ and WriteLog.
Fldigi for Multi-Mode Digital Operation
Fldigi is the most commonly used free RTTY software and supports both RTTY contest and casual operating. Fldigi is cross-platform — running on Windows, macOS, and Linux — which makes it the go-to choice for operators on non-Windows systems. It supports dozens of digital modes alongside RTTY, making it a single-application solution for multi-mode digital operation. In Fldigi, select RTTY 45 mode (45.45 baud, 170 Hz shift). Set the Mark tone to 2125 Hz in the waterfall.
WriteLog and N1MM Logger for Contest RTTY
For serious contest RTTY operating, N1MM Logger+ integrates directly with MMTTY and provides full contest logging and RTTY message macros. N1MM Logger+ is widely considered the most capable free contest logging application available and supports virtually every major RTTY contest. WriteLog is an alternative paid option with strong RTTY contest support, particularly popular in the DX and multi-operator contest community. Both programs support macro-based message transmission, which is essential for competitive contesting where speed and accuracy of exchanges determine your final score.
2Tone and Other Alternatives
2Tone is another highly-regarded RTTY decoder that many contesters use as a second receive decoder running alongside MMTTY for improved copy on weak signals. Setting up multiple, parallel decoders is "free" and provides a higher probability that one of the decoders will have clear copy, eliminating the need to request repeats. Different decoding parameters can be selected in each MMTTY and/or 2Tone instance to cover a wide range of reception conditions such as QRN, QSB, flutter, etc. MixW is a multimode amateur radio software supporting PSK31, RTTY, SSTV, Olivia, and more. It offers logging, DX Cluster, and CAT control features in a single integrated package.
RTTY Frequencies and Band Plans
HF RTTY Frequency Allocations by Band
In view of the fact that the amateur radio bands are planned so that different modes are restricted to particular areas to reduce interference and ensure the optimum use of each band, RTTY can be found in particular areas of the HF amateur radio bands. Here is a practical summary of the primary RTTY sub-bands used by US amateurs:
- 160 meters: 1.800–2.000 MHz: CW, Phone, Image, RTTY/Data
- 80 meters: 3.525–3.600 MHz: CW, RTTY/Data — primary RTTY calling around 3.580–3.590 MHz
- 40 meters: 7.025–7.125 MHz:
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