Radioteletype (RTTY)

Text sent by switching quickly between two tones. One of the oldest data modes, still used for ham contests and some weather services.

My life list

ModeRadioteletype

FamilyFSK data

Audio example12 s

RTTY sounds like a fast, even two-note warble, the tones flipping back and forth so quickly they blur into a steady 'diddle' that runs without pauses while text is sent.

What does it sound like?

Plate 54FSK data

A fast, two-note warble or 'diddle', like a rapid bird call.

0 Hz1,0002,0003,000 Hz

Waterfall picture of Radioteletype (RTTY): pitch runs left to right, time runs downward

12-second example. Recorded off the air on the developer's own receiver.

Field marksTwo tones alternating170 Hz apart on the ham bands45.45 baud on the ham bands

Hear it, step by step

This RTTY clip, recorded off the air on 80 meters, holds the end of one transmission and all of another.

Waterfall of this example: pitch left to right from 0 to 3,000 Hz, time running down

Tap a step to hear that moment. The box shows where it is on the waterfall.

Make your own: type a message and hear it as Radioteletype (RTTY) in the Signal Maker.

Who uses it?

Amateur radio contesters and operators, and utility stations such as weather services (for example, Germany's weather service sends RTTY forecasts).

Where and when can I hear it?

Ham RTTY is common around 14.080-14.100 MHz and similar spots on other bands, especially during contest weekends.

Hear it live

University of Twente WebSDR (Enschede, the Netherlands) · 7,644.5 kHz USB
Deutscher Wetterdienst weather text (DDH7, 50 baud, 450 Hz shift) around the clock from Pinneberg, Germany, according to its schedule. The 7646 kHz signal is centered in this link's passband.
Northern Utah WebSDR #1 (Northern Utah, USA) · 7,093.5 kHz USB
Weekdays at 6 p.m. and 9 p.m. US Eastern time (ARRL schedule). The order of RTTY (45.45-baud Baudot), PSK31 and MFSK16 changes by day, and not every mode is sent every day. The published 7.095 MHz sits in the middle of this link's passband.

These are free public receivers run by other people; we only link to them. You'll hear the signal only if it's on the air right now and conditions carry it to that receiver, so if it's quiet, try another time. Links last reviewed 2026-09-28.

The science

RTTY is frequency-shift keying: the transmitter flips between two steady tones, called mark and space, to send ones and zeros. Amateur RTTY normally uses a 170 Hz gap between the tones and a speed of 45.45 baud (signal changes per second), about 60 words per minute, and fits in roughly 270 Hz. Each character is a five-bit Baudot code framed by a start pulse and a stop pulse, and because five bits allow only 32 combinations, special LETTERS and FIGURES codes switch the machine between letters and numbers. There is no error correction, so a noise burst simply prints a wrong character.

Why use it?

RTTY is simple, fast to tune, and supported by most digital-mode programs, and many transceivers can generate it directly with a built-in FSK mode. Its quick, character-by-character copy makes it a favorite for contest exchanges, and its long history means a huge base of operators and equipment still speak it.

Lore

The common speeds are fossils of machinery: 45.45 and 75 baud suited North American teleprinters driven by 60 Hz synchronous motors, while 50 baud suited European machines on 50 Hz power. The unit "baud" itself is named after Emile Baudot, whose five-unit telegraph code of the 1870s is the ancestor of the code RTTY still uses.

What do the decoded parts mean?

Text: Plain text, usually in capital letters. In contests you'll hear repeated exchanges such as call signs, signal reports (599) and location or serial numbers.
Speed and shift: Speed in baud (45.45 is standard for hams; 50 and 75 are common elsewhere) and the spacing between the two tones in Hz (170 Hz for hams, 450 or 850 Hz for some utility stations).

Easily confused with

NAVTEX (maritime safety text): NAVTEX is on 518 kHz, in scheduled bursts
Pager signal (POCSAG): pager data comes in short bursts with a long preamble
Digital Selective Calling (DSC): DSC sends short bursts on marine calling channels

How to recognize it

RTTY (radioteletype) sends each character by switching between two fixed tones, called mark and space. On the ham bands the tones are 170 Hz apart and switch at 45.45 baud, which gives about 60 words per minute. On a waterfall you see two parallel lines close together.

Even when no letters are being typed, a transmitting station keeps up a steady idle pattern, so RTTY rarely has the gaps you hear in Morse. Commercial and weather services often use 50 or 75 baud and a wider 450 Hz shift, which sounds brighter and quicker.

Easily confused with:

NAVTEX and SITOR: also two tones 170 Hz apart, but at 100 baud, faster and choppier.
PSK31: one soft tone rather than two distinct notes.
Weather fax: a rhythmic scraping at two strokes a second, not a constant chatter.

Where and when to hear it

Ham RTTY is found around 14.080-14.100 MHz, 7.080-7.125 MHz in the US band plan (with 7.040 MHz a common DX spot) and 3.580-3.600 MHz. It comes alive during RTTY contests, when stations fill whole band segments; two of the biggest are the ARRL RTTY Roundup in early January and the CQ World Wide RTTY DX Contest in late September.

For a known signal, W1AW sends ARRL bulletins in 45.45-baud RTTY on a rotating schedule alongside PSK31 and MFSK16, on frequencies including 7.095 and 14.095 MHz. Outside the ham bands, Germany's weather service (Deutscher Wetterdienst) broadcasts marine weather in RTTY, including around the clock on 10100.8 kHz with a 450 Hz shift.

A little history

RTTY grew out of the teleprinter, the electromechanical typewriter-on-a-wire that carried news and business messages from the 1920s on. Militaries and news agencies moved teleprinter traffic onto radio, and after World War II radio amateurs adapted surplus Teletype machines to do the same. Early ham stations clattered with heavy mechanical printers; today a sound card and free software do the work.

Ham RTTY still uses the five-bit Baudot (ITA2) alphabet, which has only capital letters and switches between a "letters" set and a "figures" set. That is why RTTY text arrives in capitals, and why a missed shift character can briefly turn words into strings of numbers and punctuation.

Common questions

Is it legal to listen to RTTY?

Yes. Amateur RTTY and public weather broadcasts are open transmissions with published formats, and anyone may receive them.

Why does RTTY text sometimes turn into numbers and symbols?

RTTY's alphabet uses a shift code to switch between letters and figures. If noise corrupts that code, the decoder prints the wrong set until the next shift arrives. Many programs offer an "unshift on space" option to limit the damage.

What do 45.45 baud and 170 Hz shift mean?

Baud is the number of signaling elements (symbols) sent per second, so it sets the speed. Shift is how far apart the two tones are. Hams use 45.45 baud and 170 Hz; commercial services often use 50 baud and 450 Hz or other combinations.

How do I decode RTTY?

Free programs such as fldigi and MMTTY decode RTTY from a receiver's audio. Tune in upper or lower sideband so the two tones fall in the program's markers, and choose the correct speed and shift.