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RTTY (Radioteletype, pronounced "ritty") is one of the oldest digital modes in amateur radio, with roots going back to the 1930s when amateurs first connected surplus military Teletype machines to their radios. Despite its age, RTTY remains one of the most popular digital modes — especially in contesting, where its combination of speed, simplicity, and reliability has kept it relevant for decades.
RTTY uses frequency shift keying (FSK) to encode text. The transmitter shifts between two audio frequencies — called mark and space — to represent binary 1s and 0s. The standard amateur RTTY parameters are:
The Baudot code is simpler and older than ASCII. It uses 5 bits per character, giving only 32 possible codes. To accommodate letters, numbers, and punctuation, Baudot uses two "shift" states: LTRS (letters) and FIGS (figures/numbers). A shift character toggles between the two sets. This means RTTY supports uppercase letters only and has a limited set of punctuation — you won't be typing semicolons or curly braces.
At 45.45 baud, RTTY transmits at roughly 60 words per minute — faster than typical CW operating and comparable to comfortable typing speed.
There are two ways to generate the RTTY signal:
True FSK — The radio directly shifts its transmitter frequency between mark and space. This produces the cleanest signal and is preferred when the radio supports it. Many HF transceivers have a dedicated FSK or RTTY mode.
AFSK (Audio Frequency Shift Keying) — The computer generates two audio tones and feeds them into the radio's SSB audio input. The radio transmits these tones as-is within the SSB passband. AFSK is simpler to set up and works with any SSB radio, but the signal quality depends on proper audio levels. Most operators today use AFSK through a sound card interface.
Both methods produce a compatible signal — a station using FSK can communicate with one using AFSK without any issues.
Many programs support RTTY:
For contesting, many operators use N1MM Logger+ with the MMTTY or 2Tone decoding engine integrated directly, so logging and decoding happen in one application.
RTTY uses the same basic digital station setup as other HF digital modes:
If your radio has a dedicated RTTY or FSK mode, using it with true FSK produces the cleanest signal. Otherwise, USB mode with AFSK works well.
Do not use the radio's built-in RTTY filters for AFSK operation — If you are using AFSK through the SSB input, keep the radio in USB mode with a normal SSB filter. The radio's built-in RTTY demodulator is a separate system from sound card decoding and the two should not be mixed.
Audio levels — As with all digital modes, avoid over-driving. ALC should read zero. RTTY is a constant-duty-cycle mode — the transmitter is at full power for the entire duration of the transmission, so ensure your radio can handle the thermal load. Many operators reduce power to 50–75% of the radio's rated SSB output for extended RTTY transmissions.
RTTY activity is found in the digital segments of each band:
| Band | Typical activity (MHz) |
|---|---|
| 80m | 3.580–3.600 |
| 40m | 7.025–7.045 (Region 1), 7.080–7.100 (Region 2/3) |
| 20m | 14.080–14.100 |
| 15m | 21.080–21.100 |
| 10m | 28.080–28.100 |
During contests, RTTY activity often spreads well beyond these ranges as the bands fill up.
A casual RTTY QSO follows the same general pattern as other modes:
CQ CQ CQ DE W1ABC W1ABC W1ABC K
W1ABC DE G4XYZ G4XYZ K
G4XYZ DE W1ABC GA OM UR RST 599 599
NAME JOHN JOHN QTH BOSTON MA
HW CPY? G4XYZ DE W1ABC K
W1ABC DE G4XYZ TNX JOHN UR RST 599 599
NAME DAVID QTH LONDON
RIG ICOM 7300 100W DIPOLE
W1ABC DE G4XYZ K
G4XYZ DE W1ABC R FB DAVID TNX FER QSO
73 73 G4XYZ DE W1ABC SK
W1ABC DE G4XYZ 73 SK
Contest exchanges are much shorter — typically just a signal report and a serial number, state, or zone, depending on the contest rules.
RTTY is one of the "big three" modes in HF contesting, alongside CW and SSB. Major RTTY contests include:
Contest RTTY operating is fast and formulaic. Software macros handle the exchange, and the operator's job is to find stations, start the exchange, and confirm the log entry. Experienced contest operators can sustain rates of 100+ contacts per hour in good conditions.
RTTY contesting is an excellent entry point into contesting for digital mode operators. The exchanges are short and standardised, and the software handles most of the work.
Compared to PSK31, RTTY is wider (about 250 Hz vs 31 Hz) and less sensitive, but it is more robust in the presence of multipath fading and has a much longer contesting tradition. Compared to FT8, RTTY allows freeform text and has a more "human" feel, but it cannot decode signals anywhere near as weak.
RTTY's main niche today is contesting and ragchewing by operators who enjoy the mode's character and history. The distinctive warbling sound of RTTY on the bands is instantly recognisable and, for many operators, part of the charm.