Packet radio
If the APRS packet is received by an "i-gate" station, position reports and other messages can be routed to an internet server, and made accessible on a public web page.
This allows amateur radio operators to track the locations of vehicles, hikers, high-altitude balloons, etc., along with telemetry and other messages around the world.
Over 1973–76, DARPA created a packet radio network called PRNET in the San Francisco Bay area and conducted a series of experiments with SRI to verify the use of ARPANET (a precursor to the Internet) communications protocols (later known as IP) over packet radio links between mobile and fixed network nodes.
[1] This system was quite advanced, as it made use of direct sequence spread spectrum (DSSS) modulation and forward error correction (FEC) techniques to provide 100 kbit/s and 400 kbit/s data channels.
Throughout the 1970s and 1980s, DARPA operated a number of terrestrial and satellite packet radio networks connected to the ARPANET at various military and government installations.
In 2003, Rouleau was inducted into CQ Amateur Radio magazine's hall of fame for his work on the Montreal Protocol in 1978.
[citation needed] Magnuski obtained IP address allocations in the 44.0.0.0/8 network for amateur radio use worldwide.
Packet radio started becoming more and more popular across North America and by 1984 the first packet-based bulletin board systems began to appear.
Packet radio proved its value for emergency operations following the crash of an Aeromexico airliner in a neighborhood in Cerritos, California, in August 1986.
Volunteers linked several key sites to pass text traffic via packet radio which kept voice frequencies clear.
When using a direct FSK modulation like G3RUH's packet radio modem, a 9,600 baud transmission is easily made in the same channel.
A basic packet radio station consists of a computer or dumb terminal, a modem, and a transceiver with an antenna.
Increasingly, personal computers are taking over the functions of the TNC, with the modem either a standalone unit or implemented entirely in software.
Alternatively, multiple manufacturers (including Kenwood and Alinco) now market handheld or mobile radios with built-in TNCs, allowing connection directly to the serial port of a computer or terminal with no other equipment required.
The computer is responsible for managing network connections, formatting data as AX.25 packets, and controlling the radio channel.
Most commonly used method is one using audio frequency-shift keying (AFSK) within the radio equipment's existing speech bandwidth.
Due to historical reasons, all commonly used modulations are based on an idea of minimal modification to the radio itself, usually just connecting the computer's audio output directly to the transmitter's microphone input and receiver's audio output directly to the computer's microphone input.
Custom modems have been developed which allow throughput rates of 19.2 kbit/s, 56 kbit/s, and even 1.2 Mbit/s over amateur radio links on FCC permitted frequencies of 440 MHz and above.
US FCC regulations do not allow amateur radio communications to be encrypted or private, in addition to other content restrictions.
To provide automated routing of data between stations (important for the delivery of electronic mail), several network layer protocols have been developed for use with AX.25.
