Automatic Packet Reporting System (APRS)

Note:
This is a living page; the information may be confusing, incomplete, out of order, or possibly incorrect at this time. I am still learning and researching this technology.

Background

The Automatic Packet Reporting System, or APRS, was developed by Bob Bruninga (SK) for the US Navy back in the early 1980’s.

Protocol

AX.25 – https://www.tapr.org/pdf/AX25.2.2.pdf

Currently, AX.25 version 2.2 is used.

Components

Digipeater – a Digital Repeater that saves receiving packets to memory until the reception ends. When reception finishes, the data is re-transmitted on the same frequency. This allows APRS packets to travel long distances

IGate – an Internet Gateway is a station that bridges APRS packets between radio frequency (RF) and the Internet.

Global Positioning System (GPS)

Nets

#APRSThursday – https://aprsph.net/aprsthursday/

Events

Appalachian Trail Golden Packet (ATGP) – https://www.atgoldenpacket.net/
Event date is July 19, 2025

Frequencies

Region/Country	Frequency (MHz)
Argentina	144.930
Australia	145.175
Brazil	145.570
Chile	144.390
Columbia	144.390
Europe	144.800
Indonesia	144.390
Japan (1200 bps)	144.660
Japan (9600 bps)	144.640
New Zealand	144.575
North America	144.390
Russia	144.800
South Africa	144.800
Thailand	145.525
Uruguay	144.930

SSID Recommendations

-0 Your primary station usually fixed and message capable

-1 generic additional station, digi, mobile, wx, etc

-2 generic additional station, digi, mobile, wx, etc

-3 generic additional station, digi, mobile, wx, etc

-4 generic additional station, digi, mobile, wx, etc

-5 Other networks (Dstar, Iphones, Androids, Blackberry’s etc)

-6 Special activity, Satellite ops, camping or 6 meters, etc

-7 walkie talkies, HT’s or other human portable

-8 boats, sailboats, RV’s or second main mobile

-9 Primary Mobile (usually message capable)

-10 internet, Igates, echolink, winlink, AVRS, APRN, etc

-11 balloons, aircraft, spacecraft, etc

-12 APRStt, DTMF, RFID, devices, one-way trackers*, etc

-13 Weather stations

-14 Truckers or generally full time drivers

-15 generic additional station, digi, mobile, wx, etc

Position Comments

15 predetermined position comments.

Status Text

Freeform text up to 42 alphanumeric characters.

Beacon

These are position packets and can include various information.

• Speed
• Altitude

Messaging

Messages, a similar concept to text or SMS, can be sent via APRS.

Packet Path

The method to move the packets.

• New-N: WIDE1-1, WIDE2-1
• Relay
• Region
• Others

With New-N, the format is as follows. The word WIDE, indicating how far the hops should transit. The first number after WIDE is how many total Digipeaters can be traversed. The last number is the count down of hops. Just because a path is specified with 1, 2, 3, or more, does not mean the packets will only be received by three Digipeaters. Since the transmit and receive are all on the same frequency and the hops are random, many more stations may receive the packets. All this does is keep the packets from hopping an infinite number of hops. It is like a time-to-live (TTL) in TCP/IP with the number of hops allowed before the packet is dropped.

Terminal Node Controller (TNC) Speed

Speeds that are in use are 1200 baud per second (bps) and 9600 bps. 1200 bps is the most common speed in use, however. The baud must match otherwise the data packets will not be transmitted correctly. This is a similar concept to a Maximum Transmission Unit (MTU) in TCP/IP.

Objects

This is used for sending various data in a packet. There are different types of objects.

• Live Object
• Killed Object
• Live Item
• Killed Item

Latitude and Longitude, icons, and comments can be included with Objects as part of an APRS Beacon.

QSY Function

A QSY (request to change frequency) can be embedded in a position beacon transmission. The QSY function uses Automatic Frequency Reporting System (AFRS). A distance can be set for how far away the QSY can be useful.

SmartBeaconing ^TM

SmartBeaconing can be used to trigger beacons depending on configured parameters.

• Low Speed / High Speed
• Slow Rate / Fast Rate: changes the interval time of transmissions
• Turn Angle
• Turn Slope
• Turn Time

Waypoints

A waypoint is GPS location that can be stored and referenced. It can be used to advertise location.

Packet Filters

Packet filters are a way of selecting only packets of interest. This can cut down on the number of received APRS packets.

• Weather Stations
• Digipeater
• Mobile
• Object
• NAVITRA (used in Japan)
• 1-WAY
• Other

Connection to Computer

This was a difficult thing for me to figure out. Coming from a computing background, I would have just used a TCP/IP connection for networking. The concept changes when introducing a radio. Now I am learning about Terminal Node Controllers (TNC), Digipeaters, and Internet Gateways (IGate). I have an HT with built in APRS and TNC but I do not want to keep it tied up all the time to the computer. So I used another handheld and connected a Speaker/MIC cable. In this situation, I was able to listen for the APRS packets from my HT and that radio would send to the computer. Due to a technical limitation with the handheld, I was unable to transmit. But I had enough information, a proof of concept, to know in what direction I wanted to go.

Unfortunately, Kenwood/JVC does not have Linux drivers for the serial interface on the Kenwood TH-D74 required to connect the built-in TNC over Bluetooth, so I am using Windows to interface with it. But, if I want to use the Kenwood in my neighborhood, I can hook up another handheld to my Linux laptop with Direwolf, which acts as a software TNC, and let that relay the APRS packets.