AMTOR
English translation.
The AMTOR mode is a traditional mode used by radio-amateurs like
CW,
RTTY and
ASCII.
RTTY,
ASCII and 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).
.
This mode is included into the software
MULTIPSK by Patrick F6CTE, there is the description of this mode and its variants as well as the specifications coming from his software :
- 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 tranlated the best possible
way because no repetition can be requested. Therefore, receive quality
is not generally very good.
- AMTOR FEC (called also SITOR-B for the navy (as a maritime mobile service system) or simply FEC) collective B-mode
Click on the copy of the screen in order to listen to the corresponding audio signal .
Description :
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).
Recommanded frequencies for AMTOR ARQ or FEC
(OM) (USB, sometime LSB)
Same frequencies than for the RTTY 45
bauds (OM), in particular near from 14 075 KHz. See below.
RTTY 45 bauds (50 and 75 bauds - OM) in kHz
1 838-1 842, 3 580-3 600, 7 035-7 045, 10 140-10 150, 14 070-14 099, 18
100-18 109, 21 080-21 120, 24 920-24 929, 28 050-28 150, 50 100-50 500,
144 600, 144 800-144 990