Technology in Action

Hans v d Groenendaal

Amateur radio goes digital

by Hans van de Groenendaal, features editor, EngineerIT

In this monthly feature, Hans van de Groenendaal ZS6AKV, executive chairman of the South African Amateur Radio Development Trust (SAARDT), looks at various technologies and activities that drive amateur radio. SAARDT is dedicated to the development of amateur radio in South Africa, with a special interest in the youth. The organisation is funded by donations and supports the South African Radio League and SA AMSAT.

Amateur radio has not lost its ability to innovate a modest cost. The Tucson Amateur Packet and move with the times. Although digital Radio Corporation (TAPR) formed from this modes have been around from the day project. On 26 June 1982, Lyle Johnson, Marconi first transmitted radio signals in Morse WA7GXD, and Den Connors, KD2S, initiated code (which is a digital mode), the first digital a packet contact with the first TAPR unit. The communications date back to the 1940s project progressed from these first prototype when radio amateurs worked out a technique units to the TNC-1 and then finally to the of connecting mechanical teletype keyboards TNC-2, which is now the basis for most packet and printers to their radios, using frequency operations worldwide. shift keying and audio frequency shift keying. In order to provide a mechanism for the reliable However the real advancement of digital transport of data between two signalling operating modes followed the introduction terminals, it is necessary to define a protocol of personal computers, soundcards and A typical D-STAR hand-held transceiver. that can accept and deliver data over a advanced software. variety of types of communications links. The The South African Radio League has adopted AX.25 link-layer protocol is designed to provide phase shift keying (BPSK) 31 (31,25 Hz). PSK31 “Amateur radio embraces digital” for its this service, independent of any other level that is normally generated and decoded using 2014 campaign and will focus on digital may or may not exist. This protocol conforms to PC soundcards with one of many available communications technology during its various ISO Recommendations 3309, 4335 (including software packages. PSK31 occupies very small on-air activities, as well as the annual Radio DAD 1&2) and 6256 high-level data link control bandwidths (approximately 100 Hz) and offers Technology in Action roadshow which kicks off (HDLC) and uses some terminology found in effective communication at low power. There during the second half of the year. these documents. It also conforms with ANSI are many other data modes available for X3.66, which describes ADCCP, balanced experimentation, including Pactor and Clover The first major, and undoubtedly most popular, mode. This protocol follows, in principle, that enhance packet operation, and MFSK, digital mode to be developed was packet the CCITT X.25 recommendation, with the Olivia, Throb, DominoEX, MT63, and Thor which radio. It dates back to the mid-1960s and was exception of an extended address field and are other modes mainly for PC/soundcard put into practical application in the Arpanet. the addition of the unnumbered information operation. AMTOR is a special form of RTTY that which was established in 1969. Initiated in frame. It also follows the principles of CCITT provides error detection and correction. 1970, the ALOHANET, based at the University Recommendation Q.921 (LAPD) in the use of of Hawaii, was the first large-scale packet Digital voice multiple links, distinguished by the address field, radio project. Amateur began on a single shared channel. As defined, this Various digital voice applications have been in Montreal, Canada, with the first transmission protocol will work equally well in either half- or developed for amateur radio. The most on 31 May 1978. This was followed by the full-duplex amateur radio environments. popular and widely used is digital smart Vancouver Amateur Digital Communication technologies for amateur radio (D-STAR). It is Group (VADCG) development of a terminal This protocol has been designed to work a digital voice and data protocol developed node controller (TNC) in 1980. At the time equally well for direct connections between as a result of research by the Japan Amateur the Southern African Amateur Radio Satellite two individual amateur packet-radio stations Radio League. D-STAR is one of the first on- Association (SA AMSAT) acquired two of these or an individual station and a multiport air and packet-based standards to be controllers and started experimentation locally. controller. The use of packet radio for terrestrial widely deployed. D-STAR-compatible radios Soon after that the first digipeater was set up in communication has diminished but is still are available on VHF, UHF, and microwave Johannesburg. widely used in satellite communication both amateur radio bands. In addition to the for amateur radio satellites and CubeSats The current TNC standard grew from a over-the-air protocol, D-STAR also provides developed by universities. The transmission discussion in October 1981 at a meeting of the specifications for network connectivity, speeds typically range from 300 bps on the HF Tucson Chapter of the IEEE Computer Society. enabling D-STAR radios to be connected to bands to 1200 and 9600 bps on VHF or UHF. A week later, six of the attendees gathered the internet or other networks and provisions for and discussed the feasibility of developing a Today probably the most popular digital routing data streams of voice or packet data TNC that would be available to amateurs at mode is phase shift keying (PSK) 31 or binary via amateur radio callsign.

EngineerIT - Nov/Dec 2013 83