AMTOR

AMTOR (English: Amateur Tele Printing Over Radio ) is an invented word and refers to a digital mode in amateur radio. It was specially developed for the telex traffic on shortwave to compensate the occurring at these frequencies disturbances ( fluctuations of the field strength, interference ).

In AMTOR is a further development of amateur radio teletype ( RTTY ). Unlike RTTY is a process with high transmission reliability, because if an AMTOR connection, the receiving station is requested after the emission of three characters to acknowledge the error-free reception (ARQ, automatic repeat request ), or blind transfer the character redundant sends FEC ( forward error correction). In ARQ, both transmitters are alternately in operation and must quickly can switch (about 20 ms) from transmit to receive.

The principle of transmission of telex characters after the ARQ or FEC methods exist in the commercial marine radio under the name SITOR, SPECTOR or Microtor and was appropriately modified for amateur radio.

To carry out the operation AMTOR controllers are required, which are connected between the terminal (usually an ordinary PC) and the transceiver. There is also free software that generates the signals with a sound card and does not require a special controller more.

Modulation

AMTOR uses AFSK with two tones and a synchronous transmission with error correction as Pactor but with 7 bits per character.

The transmission of the signals takes place, as in RTTY, by frequency with the same tones and the same shift. Called The higher frequency you Mark and the lower space. They lie to the shift apart ( frequency difference). On shortwave the shift is 170 Hertz, to ultra-short wave (VHF / UHF) 850 Hz three blocks are transmitted at 100 baud. At 100 baud which is 10 milliseconds, for a bit 1/100 second, are needed. A 7-bit character requires 70 ms and for a block of three so 210 milliseconds are required. The three blocks are sent at an interval of 450 ms, so that the other station is a gap of 240 ms remaining to send its check mark. The time for the receiving-transmitting switching must therefore be very short in this mode. The bandwidth is 500 Hz AMTOR is increasingly replaced by the newer and better methods Pactor.