AMTOR use two frequencies which are filtered, each one corresponding to a binary digit (1 or 0). These two frequencies, separated by a shift, modulate the RF when transmitted and the modulation is called Audio Frequency-Shift Keying (AFSK), otherwise the modulation can be done directly on the RF carrier and it is called Frequency-Shift Keying (FSK).
Baud rate : 100. A character is composed of 4 « space » and 3 « mark » bits. It is an uninterrupted stream of characters, contrary to AMTOR ARQ.
Speed : 71 wpm
Modulation : FSK two tones (« mark » and « space », "mark" high) with a shift between tones of 170 Hz
Reception mode : USB
Character set : CCIR476-4 (32 letters, 32 figures and 6 control, idle or phasing signals) with no 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 »)
Shape of pulse : rectangular
Bandwidth : about 800 Hz (due to rectangular shape),
Demodulation : non coherent
Synchronization : automatic using the signal
Correction code : no
Convolution code : no
Interleaving : each character is repeated 5 positions later (that is 350 ms between 2 transmissions of the same character). This diversity in time allows the correction of an erroneous character. Its detection is easy due to the particular content of a character (4 « space » and 3 « mark »).
Pmean/Ppeak : 1
Lowest S/N : about -5 dB
Note : There are 2 FEC modes: the collective B-mode (described before) and the selective B-mode (little differences as an inversion of bits)
This mode is not used very much at all and the FEC part of AMTOR is not real strong slight bit more advantage to RTTY but does not handle the ionspheric disturbances all that great..AMTOR suppose to been a improvement over RTTY
FEC or SITOR-B
FFT Screen Shot
Mode Audio Sample