RTTY decoder for radio teletype
RTTY is radio teletype using two tones. Signal-Pirat decodes it from a recording or live via the receiver output and creates RTTY audio for practice. Mark tone, shift, baud rate and polarity are adjustable.
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What the page does
- ITA2 code with US-TTY or ITA2 figures
- 45.45, 50 or 75 Bd; shift 170, 425 or 850 Hz
- Mark tone is detected in recordings
- Squelch against false characters in signal gaps
- Error-free in test runs from about 3 dB SNR
Background
Each character consists of one start bit, five data bits and one and a half stop bits; mark and space are two tones separated by the shift. Letters and figures share the 32 codes, switched with LTRS and FIGS. The decoder compares both tones over one bit, detects the start bit at the edge and checks the stop bit.
In practice
How it works: tune the receiver in LSB to an RTTY signal so both tones are in the audible range. For recordings the decoder finds the mark tone itself; live it is set manually. If only garbage appears, the polarity is often reversed: switch the polarity. Figures and punctuation after a space are read correctly according to the usual rule.
Frequently asked questions
Which settings do I need for amateur RTTY?
Usually 45.45 Bd and 170 Hz shift, received in LSB. These values are the default.
What does the squelch do?
It only passes characters where one tone clearly dominates at every sampling point. It can be switched off for very weak signals.