User`s manual

Tracker3 User’s Manual 4
connection and a radio, pass traffic from the radio network to a shared,
worldwide APRS stream. Many IGates will pass at least text message traffic, and
sometimes other data, from the Internet back to the radio network. In this way,
text messages can be passed from one station to another even when a digipeater
path between the two doesn’t exist or isn’t reliable.
The name APRS is also sometimes used to refer to WB4APR’s original MS-DOS
APRS mapping program, but this is now properly called APRSdos. Numerous
other mapping and messaging programs exist, using either the APRS radio
network, the APRS-IS, or both. Some of these programs can function as IGates as
well.
Connected to the worldwide APRS-IS stream are a number of database services.
These systems (aprs.fi and openaprs.net are two of the most popular) process
and store all APRS traffic that finds its way to an IGate anywhere in the world,
and most provide maps, weather displays, and telemetry graphs based on this
traffic. This allows anyone with Internet access to monitor APRS data without
needing radio equipment of their own or special software.
Getting data to a web-connected database isn’t the only thing APRS is good for,
of course. Depending on network coverage and load, it’s possible to
communicate over a range of hundreds of miles using the radio network alone.
However, being a shared network, reliability decreases with each added
digipeater hop. APRS is most reliable at the local level, and it’s rarely advisable
to use more than two or three digipeater hops. Often, a single hop is adequate
for local coverage.
The APRS protocol, hardware, and software can be used independently of the
national networks, as well. Local or temporary networks may be set up to cover
special events or to fill the needs of a particular organization. Some uses may not
require digipeaters at all – high altitude balloons, for example, often use APRS to
transmit position and telemetry data on a dedicated frequency directly to the
chase teams.
Mobile use of APRS can take a number of different forms. The simplest mobile
APRS setup is a transmit-only tracker connected to a radio and GPS receiver.
These trackers generally have no receive capability, other than to check that the
channel is clear before transmitting. They allow the vehicle to be tracked by
others, but can’t receive messages or positions.