Description : Baud rate : 45. A character is composed of a « start » bit (1 « space »), 5 bits and a « stop » bit (1.5 « mark ») Speed : 60 wpm Modulation : FSK two tones (« mark » and « space », "mark" high) with a shift between tones of 23 Hz, 170 Hz (standard shift), 200 Hz or 850 Hz, Note: in RTTY 45 bauds, shift=23 Hz, the modulation is specific and called "MSK" (Minimum Shift Keying). The demodulation is not done with two filters (as in FSK) but is done using phase measures. The RTTY 45 bauds, shift 23 Hz MSK mode, from MMTTY, has been created by Makoto Mori, JE3HHT around 2003. Receive mode : USB Character set :ITA2 (32 letters and 32 figures) without error correction character (« fixed length » characters). Small characters are transformed in capital characters and special characters as « é » are transformed in standard capital (in the example: « E »). The "Unperforated tape" character is obtained through the ASCII valor CHR(1). It might be used for a characters set change (russian characters to latin characters for example). Shape of pulse : rectangular Bandwidth : for the standard shift of 170 Hz, about 600 Hz (due to rectangular shape), Demodulation : non coherent, Synchronization : on « start » Correction code : no Convolution code : no Interleaving : no Pmean/Ppeak : 1 Lowest S/N : -5.5 dB In 50 bauds, the speed is 67 wpm and the lowest S/N is -5 dB. In 75 bauds, the speed is 100 wpm and the lowest S/N is -3.5 dB. The 850 Hz shift mode is intended to old teleprinters.
What is ASCII? ASCII Radioteletype ("ASCII" for short) uses the same modulation methods (frequency shift keying) as RTTY. The main difference is that ASCII character encoding is used in place of Baudot character encoding.
Baudot consists of 5 bit codeword. Since 32 states are insufficient to encode letters, numbers and punctiations, the Baudot code is partitioned into two tables. Two special non-printing characters, one character is sent to shift the decoder into the "letters" (LTRS) table and the other character is sent to shift the decoder into the "figures" (FIGS) table which include numbers and punctuations. When a LTRS or FIGS character is misdecoded (or some other character is misdecoded into a LTRS or FIGS character), subsequent characters can be wrong until the proper LTRS/FIGS state is again restored.
Standard ASCII consists of 128 usable codewords, and not only can it uniquely encode letter, numbers and punctuations in the same table, the table is large enough includes both upper case and lower case alphabets.
Unlike Baudot, ASCII includes a backspace character. Like PSK31, you can correct typing errors by backspacing over previous characters in ASCII.
RTTY has one of the strongest presence on HF bands , due to it has been around a long time and lots of contests support the use of RTTY, Lots of major Dxpenditions use this mode as there default mode for Digital mode operations.
RTTY is not necarrissly the best digital mode, but is forgiving on tuning, when many stations are on the air RTTY can be covered up by the splash over of the effective bandwidth of other operators on the air sometimes making it more difficult to decode. The Signal noise ratio is fair , lots of stations do use amplifiers on this mode as well. With the fair speed of the mode makes it a nice mode to work many stations, but other modes have comparable speeds as well. Most RTTY operations are done on 45.45 baud at 170hz shift and always use USB when using AFSK or modulating with audio into the radio , FSK is controlled by software which the radio is shifting instead of audio thus the radio is shifting instead of only audio shifting . FSK is superior in this sense, The radio has tight filters when put into RTTY mode or FSK mode, in AFSK mode usually you only can use the SSB filter. RTTY is condsidered a hard shifting mode makes the effective bandwidth much greater than the shift itself. RTTY can suffer from selective fading going across pole paths, sometimes the mark or space side of the signal can completely dissapear making errors on decoding