APRS was designed by Bob Bruninga, WB4APR. He presented it publicly in 1992 at the TAPR/ARRL Digital Communications Conference, but its roots go back further: in 1982 on an Apple II at the United States Naval Academy, and in 1984 a VIC‑20 version tracked horses in a 100‑mile race. Bruninga died on 7 February 2022. In the 2000 APRS101 specification the acronym expands as Automatic Position Reporting System; today you’ll more often see Automatic Packet Reporting System.
An APRS packet is an AX.25 UI frame: sent to everyone at once, with no link‑layer acknowledgement. On VHF it most often goes at 1200 baud with AFSK modulation, i.e. two tones: 1200 Hz and 2200 Hz, as in a Bell 202 modem.
A digipeater receives a packet and retransmits it so it reaches further. The path in the packet says how many times it may be repeated. IARU Region 1 adopted the “New‑N” rules in 2008: a fixed station uses WIDEn‑N with N of at most 2, and a mobile station uses WIDE1‑1,WIDEn‑N, again with N up to 2. The typical recommended default path is WIDE1-1,WIDE2-1, i.e. two hops: the first via any digipeater, including a small “fill‑in”, the second only via a wide‑area digipeater. The aliases RELAY, WIDE and TRACE are obsolete and should not be used.
An iGate forwards the packets it has heard on the air to the APRS‑IS internet network. A bidirectional gateway can also transmit messages from the internet to local stations. The aprs.fi service uses APRS‑IS, where positions are shown on the map.
