RTTY — Radioteletype Operating Guide
RTTY (RadioTeleTYpe) is the oldest digital mode in amateur radio, with roots in the mechanical teletype machines of the 1950s. Modern RTTY uses software to generate and decode the same 170 Hz frequency-shift keyed (FSK) audio tones that mechanical teletypes once produced, making it fully compatible with both traditional hardware and modern sound card setups. 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.
FSK and AFSK
RTTY uses Frequency Shift Keying — the carrier frequency shifts between two tones (Mark and Space) to represent binary data. 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.
Two connection methods are used: AFSK (Audio Frequency Shift Keying) sends the Mark and Space tones through the radio's audio input, requiring a sound card interface. FSK uses the radio's FSK input to directly shift the transmitter frequency — this is cleaner and preferred for contest use with radios that support it (most modern HF transceivers do).
RTTY 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.
Software options
Fldigi is the most commonly used free RTTY software and supports both RTTY contest and casual operating. MMTTY is a dedicated RTTY program popular among contest operators for its accurate decoding and MMVARI decoder. For serious contest RTTY operating, N1MM Logger+ integrates directly with MMTTY and provides full contest logging and RTTY message macros. 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 for RTTY
Connect your radio to your computer via a sound card interface or USB audio. Set your radio to USB mode (RTTY-specific mode on some radios uses LSB — check your radio's manual, as the convention varies). In Fldigi, select RTTY 45 mode (45.45 baud, 170 Hz shift). Set the Mark tone to 2125 Hz in the waterfall. Audio levels for RTTY follow the same rules as other digital modes — set ALC to barely deflect, use the minimum drive needed for the contact.
Contest exchange
In RTTY contests, the exchange is highly standardised and uses macro keys for speed. A typical RTTY contest contact: you call the running station's CQ, they come back to you with your callsign and a signal report plus exchange (e.g., "W4ABC 599 14"), you confirm and send your exchange ("R 599 ND"), they send a final confirmation ("TU"), and the contact is logged. The entire exchange takes 20–30 seconds. RTTY contest macros in N1MM Logger+ or Fldigi handle the repetitive text automatically.
Major RTTY contests
CQ WW RTTY (September) and BARTG RTTY Sprint (March) are the two largest dedicated RTTY contests. ARRL Sweepstakes has an RTTY category in some formats. The WPX RTTY contest in February is also popular. RTTY Roundup (January, ARRL sponsored) is an excellent first RTTY contest — straightforward exchange, friendly atmosphere, and widely supported by logging software.
| Band | RTTY Range | Notes |
|---|---|---|
| 80m | 3.570–3.600 MHz | Regional — active in RTTY contests |
| 40m | 7.040–7.100 MHz | Day and night — busy in contests |
| 20m | 14.070–14.099 MHz | Most active RTTY band worldwide |
| 15m | 21.070–21.110 MHz | When open — good DX |
| 10m | 28.070–28.150 MHz | Excellent DX at solar max |
Is RTTY difficult to set up compared to FT8?
RTTY requires more careful audio level calibration than FT8 because it is more sensitive to audio distortion. FT8 is more forgiving of imperfect levels. However, basic RTTY operation — particularly receive-only monitoring to learn the mode — is straightforward with Fldigi. The main complexity in RTTY comes from contest operating with macros and dual-decoder setups, which is an intermediate topic.
What is the difference between RTTY and PSK31?
Both are HF digital text modes, but they use different modulation schemes and have different characteristics. 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. Both are active modes with overlapping but somewhat different operating communities.
Can I use my radio's built-in RTTY mode?
Many modern HF transceivers have a dedicated RTTY operating mode that handles the FSK keying directly through a rear-panel FSK input. This is actually cleaner than AFSK through the audio path and is preferred by serious RTTY contesters. Check your radio's manual for RTTY FSK input specifications. If your radio supports FSK RTTY, use it in conjunction with MMTTY or Fldigi configured for FSK output through your interface.
What are DIDDLE characters in RTTY?
DIDDLE is the continuous transmission of Figures (FIGS) shift characters during pauses in RTTY transmission — when the operator is not typing. It serves two purposes: it keeps the transmitter keyed (preventing the ALC from resetting between characters) and it prevents the receiving station's decoder from losing sync during pauses. Contest RTTY macro software typically handles DIDDLE automatically.