Digital communications refers to the transmission of digital data, in contrast to analog communications.
Analog communications use a continuously varying signal, a digital transmission can be broken down into discrete messages. Transmitting data in discrete messages allows for greater signal processing capability. The ability to process a communications signal means that errors caused by random processes can be detected and corrected. Digital signals can also be sampled instead of continuously monitored and multiple signals can be multiplexed together to form one signal.
Because of all these advantages, and recent advances in wideband communication channels and solid-state electronics, scientists have fully realised these transmission systems. Digital communication has grown quickly in the commercial world, edging out analog communication, because of the vast demand to transmit computer data and the ability of digital communications to do so. Digital communication has always had a place in Amateur Radio.
It is often overlooked as being a digital mode but CW (Morse Code) is really the first digital mode utilised in radio communications. From the birth of radio until just after the second world war CW was the only digital mode in common use. The end of the second world war saw a large amount of surplus military teletype equipment available so radio teletype (RTTY) became very popular. This changed little until the 1970's when the very first personal computers arrived so noisy teletype machines were replaced with keyboards and screens. This enabled amateurs such as Peter Martinez G3PLX to devise a new system for transmitting data over radio, called AMTOR (AMateur Teletype Over Radio). AMTOR was loosely based on a commercial protocol called SITOR and for the first time, allowed very simple error detection techniques to be incorporated into the data stream.
Throughout the 70's development progressed across the world with different digital modes until 1982 when the X.25 packet radio standards were finalised. Development has continued with further enhancements to AMTOR and the new PACTOR and CLOVER modes were introduced.
Packet Radio (x25)
Project 25 (P25)
Voice Over Internet Protocol (VoIP)
All above courtesy of Brian Perrett and Highfield Amateur Radio Club
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