Radioteletype

Radioteletype often shortened to RTTY and pronounced "Ritty" or sometimes called Baudot or ITU-2 after the character encoding used (for reference ASCII is the standard for computers and is also used over radio but is very rare, ITU-2, which was originally called baudot and started off as a telegraph code is the standard for RTTY)

It transmits the 5-bit per character ITU-2 encoding via FSK, the exact baud rate and frequency shift depends on the kind of RTTY used, but the low baud rate and FSK modulation gives it a very distinctive "beedle-eedle" sound.

RTTY is what's known as a Keyboard-To-Keyboard mode, operating RTTY is sort of like text messaging albeit with some extra ettiquette for each side to understand when a message is finished and when they can start transmitting, some of the prosigns such as "SK" and "GA" are identical to those used in CW and also TDD (a form of AFSK RTTY over telephone lines used by deaf people before text messaging became common place).

Historically RTTY was sent and received via a teletype machine or terminal and a hardware modem, these days a computer with a soundcard/software modem is all what is needed.

Video

2022.08.30 - "Saturday Ham Radio RTTY Teletype Vintage Net" by Ray Fantini
2020.12.19 - "Telereader CWR-685E, RTTY Context, YL2CI FB" by Frank the Tank
2020.03.31 - "RTTY with 1960's US Navy Equipment" by Nick England
2021.01.24 - "ARRL RTTY Roundup Jan 2-3 2021 the old fashioned way." by Old Fellow's Toys
2019.02.12 - "MY FIRST RTTY QSO WITH A MECHANICAL MACHINE" by Helge Fykse
2017.12.08 - "RTTY on teh Teletype Model 28 KSR" by Ethan Blanton
2015.01.22 - "FLDIGI Tutorial How to decode amateur radio RTTY signals" by OfficialSWLchannel

fldigi modes
Contestia	CW	DominoEX	Hellschreiber	MFSK	Olivia	PSK	Radioteletype	THOR

Digital modes

Contestia

CW

DominoEX

FT4

FT8

Hellschreiber

MFSK

Olivia

PSK

Radioteletype

THOR

THROB

WSPR