The Automatic Packet Reporting System (APRS), developed by Bob Bruninga, WB4APR, distributes short reports about station activity and local conditions. It can carry positions, messages, weather, status, telemetry and named objects. Older documents also use “Automatic Position Reporting System”; position reporting is only part of its purpose.
Conventional VHF APRS commonly uses AX.25 packet radio with 1200-bit/s audio frequency-shift keying through an FM transmitter. Tone frequencies are commonly 1200 and 2200 Hz. The RF channel varies by region and must match the local network.
Most routine reports use AX.25 unnumbered information (UI) frames rather than establishing a connected link first. Stations share the same radio channel, so frequent reports and long forwarding paths consume capacity for everyone.
A digipeater receives and retransmits eligible packets over radio according to the packet's path and local configuration. An IGate exchanges eligible traffic between RF and the APRS Internet System, APRS-IS. Not every IGate transmits Internet traffic back onto RF.
The path in a packet describes requested forwarding behaviour. Choosing more hops does not automatically improve communication: duplicate transmissions, collisions and distant traffic can overload a local channel.
Position formats encode latitude and longitude or use compressed representations. Symbols describe a station or object; telemetry can report measurements. APRS messages support acknowledgements, while a broadcast position report is not a guaranteed-delivery message.
For an illustration of channel time, 100 bytes alone need at least:
Time = 100 × 8 / 1200 ≈ 0.667 s
Actual radio airtime is longer once framing, bit stuffing, preamble and transmitter start-up are included. This is a lower-bound calculation, not a full packet airtime formula.