AMTOR, also known as Amateur Teleprinting Over Radio, is a mode of digital communication used primarily by amateur radio operators. It is a protocol designed to transmit and receive text messages over radio waves.
In AMTOR, the message is divided into small packets, each consisting of a start bit, data bits, and a stop bit. These packets are then transmitted using a combination of frequency shift keying (FSK) and shift state modulation (SSM). The FSK technique involves shifting the carrier frequency between two predetermined frequencies, representing binary values of either "0" or "1". On the other hand, SSM is employed to indicate a positive or negative state change, determining the shift of the transmit frequency.
The advantage of AMTOR is its ability to overcome significant noise and interference commonly found in HF (high-frequency) radio channels. It utilizes error detection and correction techniques, such as cyclic redundancy check (CRC) codes, to ensure accurate message reception even in a noisy environment. Additionally, AMTOR incorporates features like automatic repeat request (ARQ), which enables retransmission of lost or corrupted packets.
AMTOR is commonly used by amateur radio operators for sending formal messages, weather reports, and other non-real-time information. It provides a reliable means of communication, particularly over long distances, where voice communication may be less effective. It requires specialized equipment capable of encoding and decoding the AMTOR signals, commonly found in modern radio transceivers or through a computer with dedicated software.
