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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).

- AMTOR ARQ (called also SITOR-A for the navy (as a maritime mobile service system) or simply TOR)

Description :
Baud rate : 100. A character is composed of 4 space and 3 mark bits. A block of characters (called Block 1 or Block 2 ) is composed of three characters (total duration: 3 x 70 = 210 ms) and a pause of 240 ms duration. During this pause, the receiving station emits a control signal of 70 ms duration to say please next block (symbol "ACK" for acknowledge) or to ask for a repetition of the last block, in case of erroneous character (symbol "NACK" for not acknowledge)

Speed : between 0 and 67 wpm (67 wpm corresponding to the 50 bauds RTTY) depending of the number of repetitions
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 reset character ( fixed length characters).
In SITOR A, the character set may be extended to the Cyrillic characters by using the character for un-perforated tape (third shift).
In AMTOR A, the character set may be extended to the ASCII characters (32 to 128) by using the character for the un-perforated tape

Shape of pulse : rectangular
Bandwidth : about 800 Hz (due to rectangular shape),
Demodulation : non coherent
Synchronization : automatic using the signal
Correction code : yes via automatic repetition and easy detection of an erroneous character due to the particular content of a character (4 space and 3 mark bits)
Convolution code : no
Interleaving : no
Pmean/Ppeak : 1
Note : In AMTOR ARQ LISTEN, characters are translated the best possible way because no repetition can be requested. Therefore, receive quality is not generally very good.

MORE ON AMTOR FEC SITOR-B for the Navy CLICK HERE


+Handles ionspheric effects fairly well
-Not used much
-not used much



Mode Menu
AMTOR
ARQ MODE or SITOR-A
FFT Screen Shot
Mode Audio Sample
AMTOR