radio teletype (RTTY)
Radio Teletype (RTTY) means radio teletype and corresponds to teletype transmitted by radio. It is a classic telecommunications service operating on shortwave and used in amateur radio and the transmission of weather reports. The transmission rate is relatively low at 10 to 1,000 baud.
In radio teletype, the digitalinformation is transmitted asynchronously with frequency shift keying( FSK) or audio shift keying( AFSK). The information is encoded in the teletype code, according to the IA-2 alphabet. This code is also known as Baudot code. Synchronization is ensured by a start bit and several stop bits. The two modulation tones located in the speech area represent the digital states "Mark" or "1" and "Space" or "0". Their frequencies are 1275 Hz and 1445 Hz or 1995 Hz and 2125 Hz.
Depending on the modulation method, radio teletype works with different modulation codes. For frequency shift keying it is F1B, which means frequency modulation with single channel and digital information for telegraphy, or for tone shift keying it is A2B and F2B, which means digitally transmitted information in double sideband or frequency modulation for telegraphy.