Aprs.fi user guide

This is the official manual for the aprs.fi web service. This is also a Wiki page, so you're welcome to expand the document!

Introduction

The aprs.fi web service collects information from the Automatic Packet (or Position) Reporting System Internet network (APRS-IS). APRS is used by amateur (ham) radio operators to transmit real-time position information, weather data, telemetry and messages over the radio. A vehicle equipped with a GPS receiver, a VHF transmitter or HF transceiver and a small computer device called a tracker transmits it's location, speed and course in a small data packet, which is then received by a nearby iGate receiving site which forwards the packet on the Internet. Packets are also retransmitted on the radio channel by digipeaters to enhance the coverage of the system. Systems connected to the Internet can send information on the APRS-IS without a radio transmitter, or collect and display information transmitted anywhere in the world.

In addition to that, aprs.fi also displays AIS data transmitted by most large ships. AIS transmissions are received by volunteers at numerous sites, but most areas are largely uncovered.

This guide aims to become a comprehensive manual for the aprs.fi web site, and as such does not attempt to describe the APRS or AIS systems in detail. To get started with APRS, please consult the following pages:

• Wikipedia: Automatic Packet Reporting System
• G4ILO: APRS - Putting ham radio on the map
• K9DCI: APRS Beginner Guide (PDF)

AIS is described well on the Wikipedia page for Automatic Identification System.

Languages and localisation

The aprs.fi service has been translated by volunteer users to numerous different languages. The language shown to you will be selected based on your browser's language preference settings. If you wish to preview the site in different languages, please prepend the two-letter language code to the site URL:

• http://fi.aprs.fi/ - aprs.fi in Finnish
• http://ja.aprs.fi/ - aprs.fi in Japanese
• http://en.aprs.fi/ - aprs.fi in English

The site also supports different measurement units (metric, imperial and nautical), which can be selected in the preferences.

Site navigation links

Each page has a set of navigation links at the top of the page, and another at the bottom. On the real-time map, the links are provided in the navigation bar the right side of the map, which can be hidden by clicking the button in the top right corner of the page.

The general idea is that the links on the top provide links to different data views. If you have already looked up a specific station, the links will contain that callsign, and clicking on the weather link when viewing the info page of a weather station will give you that station's weather history graphs.

The links at the bottom page provide links to static content pages such as the FAQ and this user guide, which give general information about the whole site.

There are a few exceptions to these rules, of course – the My account and Moving stations links, for example.

Sections

Aprs.fi Common features

Aprs.fi Real-time map

Aprs.fi Preferences

Aprs.fi Info pages

Aprs.fi Static maps

Aprs.fi Weather

Aprs.fi Telemetry

Aprs.fi Network tools

Aprs.fi Exporting data

Aprs.fi Troubleshooting

Messages

The message browsing page displays APRS chat messages sent between users. Initially it shows the most recent messages seen on the APRS-IS. If you look up a callsign, you will see all messages sent by or destined to that call. Messages sent by the station are shown with a red background, and received ones are shown in green.

aprs.fi currently does not have the possibility to transmit messages (or any other type of data), it serves only as a place to view data.

Status messages

Status message packets are shown in the status message page. Initially, if opened without a callsign, it will let you browse the stations which have transmitted status messages, sorted by callsign. If you look up a callsign, you get to browse old status messages transmitted by that station over time.

Difference between status messages and comment text

Status messages are often confused with the comment text. They're another method to send some descriptive status message for the station, the difference from comments being:

1. The comment text is transmitted in the same APRS packet with the position, as text right after the position data. aprs.fi associates the comment message with the position.
2. The status message is transmitted in a separate APRS packet, such as the following one, together with a timestamp. On aprs.fi, the status message is stored separately from the position, and they can be browsed using the status message page.

 2010-07-02 10:09:00 UTC: CT2XXX-11>APU25N,WIDE3-3,qAR,CT1AKV:>282308zUI-View32 V2.03

As you can see from this example, the timestamp is quite often invalid, so it is ignored by aprs.fi. In practice, you can put your descriptive message in the comment text or the status message. It is not wise to put the same text in both comment and status, as it will then be sent twice, which will place unnecessary load on the busy APRS network.

Beacon packets

The beacons page shows packets received from the APRS-IS but which were not identified as APRS packets at all. They are typically identification beacons sent by network nodes, usually describing their hardware or software.

 2010-07-02 03:44:07 UTC: DB0EMS>UIDIGI: UIDIGI 1.9
 2010-07-02 03:44:38 UTC: DB0UAL>ID: DB0UAL * X-NET-DIGI * -9k6 Shift

Bulletin board

APRS bulletin messages are used for sending local announcements to other APRS network users. The aprs.fi Bulletin board page shows all bulletins which have been transmitted recently and passed on the APRS-IS. The page allows looking up custom bulletin groups using the links provided in the beginning of the page.

Raw packets

The raw packets page allows you to browse and inspect APRS packets received from the APRS-IS. When you load the page initially (or click Clear) it will show the most recent APRS packets received. The previous and next buttons can be used to browse older ones. If you click on Raw packets in the real-time map while tracking a station, you will automatically get the packets sent by that station.

Invalid packets (and ones which are valid but which are not supported by aprs.fi) are shown in red, together with an English error message. Unprintable non-ASCII characters are displayed in hex with a purple colour. <0x1c> stands for a byte which has a hex value of 1C (28 decimal).

To see a hex dump of the complete packet contents (revealing difference in whitespace: tabs, amount of space characters in the end of the line), move the mode selector from Normal to Hex.

To view the decoded contents of the packets, switch to the Decoded mode. This will display what information the Ham::APRS::FAP APRS packet parser is able to find from the packets, and is very useful for understanding the contents of mic-e and compressed format packets. aprs.fi internally uses the open-source Ham::APRS::FAP parser for decoding.

Prefix browsing

The prefix browsing pages allow you to search for APRS users by the callsign prefix. It's useful for finding APRS users near you, even if they haven't transmitted for a while and are not shown in the real-time map.