APRS Packet Types

APRS Packet Types

Every APRS transmission is a packet — a structured bundle of data with a source callsign, destination, path, and payload. The payload's first character (the data type identifier) tells receiving stations what kind of information follows. Here are the main types you'll encounter:

Position Packets

Position packets are the most common APRS transmission. They contain:

• Latitude and longitude — Where the station is located
• Symbol — An icon representing the station type (car, house, weather station, etc.)
• Comment — Optional free-form text (e.g., "Mobile on I-95" or "Solar powered")

Position packets come in three encoding formats: uncompressed, compressed, and Mic-E (a compact encoding used by many handheld radios and mobile trackers).

Weather Packets

Weather stations transmit periodic reports containing some or all of:

• Temperature
• Wind speed and direction
• Wind gusts
• Rainfall (last hour, last 24 hours, since midnight)
• Barometric pressure
• Humidity

These stations form a distributed weather monitoring network, often filling gaps in official weather service coverage.

Message Packets

APRS supports three messaging modes:

• Direct messages — Addressed to a specific callsign, with acknowledgment
• Bulletins — Broadcast messages visible to all stations
• Group messages — Sent via gateways like ANSRVR to subscribers of specific groups

Messages are limited in length but support a reliable delivery mechanism through acknowledgment packets.

Status Packets

Status packets are simple free-form text broadcasts. Operators use them to share:

• Current activity or operating frequency
• Equipment information
• Event participation
• Club or net announcements

Unlike messages, status packets are not addressed to anyone — they're informational broadcasts.

Telemetry Packets

Telemetry packets carry numeric sensor data in a structured format:

• Up to 5 analog channels (e.g., battery voltage, temperature, solar current)
• 8 digital bits (on/off states)
• Separate definition packets describe channel names and units

Telemetry is commonly used for remote site monitoring — solar installations, repeater sites, and environmental sensors.

Object and Item Packets

Objects and items are special position reports placed by a station on behalf of something else:

• Objects — Can be updated or deleted by the originating station (e.g., a net meeting point, a storm cell)
• Items — Simpler, typically static markers (e.g., a trailhead, a point of interest)

These allow operators to annotate the map with relevant information that isn't tied to a physical transmitter.

Identifying Packet Types

On this dashboard, each packet is labeled by type and color-coded for quick identification. The Decode tool (Cmd+K) lets you paste any raw APRS packet to see its full breakdown and field-by-field explanation.