Updated 01/23/2003 01:09 AM
those not familiar with the Automatic Position Reporting System
(APRS), the most important thing to understand is that APRS is not just a
communications tool like Packet or RTTY, but rather a whole set of tools -
a toolbox if you will - all designed to work together. All of these tools
designed to facilitate the management of any team effort across a wide
take a peek inside this toolbox and see what we find:
Information Systems: APRS provides for the display of
data on a wide variety of maps. Virtually any map which may be displayed
on a computer may have APRS data displayed over it. The display may be in
two dimensions (position on the earth's surface) or three dimensions
(including altitude). Some of the items typically displayed on a map
include: storms, weather observations (e.g. temperature, wind speed. etc)
airplanes, moving vehicles, runners, bicycles, shelters, ham stations,
homes, businesses, fires, accidents, etc.
Software: This is the tool which ties all of the parts
together and sorts incoming data into meaningful tables. The APRS software
may be run on virtually any computer which supports one of the following
operating systems: MS DOS (ver 2.0 and higher), MS Windows (ver 3.0 and
higher), MS Windows CE, Macintosh, LINUX, and Java. APRS programs have
also been written for a variety of postage-stamp processors, and at least
two Kenwood and one Alinco receivers. This software provides for the
handling of all of the following types of data: position reports, status
reports, objects, weather reports, storm data, shelter data, telemetry,
messages traffic, bulletins, warnings, and beacons.
Positioning Satellite (GPS) Systems: The Global
Positioning Satellite System allows users to pinpoint their exact location
on the surface of the earth (or above it). Typically, a small antenna,
about the size of a computer mouse can provide digital data containing the
latitude, longitude (and sometimes altitude) of the device. When this data
is input to the APRS system, all users can see the exact location of that
device on a map as it moves. For example, a mobile ham unit (car) using
APRS could have its location constantly reported to an EOC (Emergency
Operations Center). APRS can also work with LORAN systems used in the
Radio Packets Packet Radio is a system invented by hams
to transmit digital data over radio circuits designed for voice. Data to
be transmitted is split into small units called packets
and then converted to audio tones (often via FSK) and transmitted as an
audio signal. On the receiving end, the tones are converted back to
digital data and assembled into the original stream of data. UI
refers to Un-numbered Information, which is a specific type of packet
which does not require acknowledgement (the data equivalent of a voice
broadcast). Radio frequencies most commonly used by APRS include 144.39
Mhz, 7.085, 10.151, and 18.107 Mhz LSB. However, APRS packets may be
transmitted over almost any voice channel, including over police radios,
amateur repeater systems, business band, marine band, Citizen's Band, cell
phones and even land-lines.
Digipeater Network In the 2-meter band, APRS stations
may have as little as 1 watt of power and yet have their packets reach
stations as far as 400 miles away. This is accomplished by a network of
dedicated digital repeaters (digipeaters)
which relay signals over long distances. To avoid network saturation,
packets are normally repeated only three times, hence the 400 mile limit.
For mobile users in remote areas not served by digipeaters, packets may be
repeated via orbiting satellites. The mobile station requires a 10 watt
output and a 5/8-wave antenna to uplink a signal on 144.90 Mhz.
In addition to staying in touch by radio, APRS can take advantage of the
Internet to transmit data to stations out of radio range, or to stations
not equipped with radio capabilities. By design, APRS data is only
transmitted about 400 miles by radio. However, the Internet allows users
all over the world to exchange data when desirable. Virtually any computer
with APRS software and a modem may receive data from the APRS-Net.
(ISP not required!)
For computers not already connected to a network, a very inexpensive
serial data network may set up to provide all users access to APRS data.
This would be helpful in a police headquarters or EOC where there may be
computers that normally work independently, but all need access to APRS
information during an emergency.
Stations Inexpensive weather monitoring equipment may be
connected to an APRS station to provide a continuous stream of weather
observations from the station's location. Parameters such as temperature,
wind speed (gust and sustained) and direction, barometric pressure,
rainfall and relative humidity are often available on a real-time basis
from locations all around a major city. This data can be of enormous value
to weather forecasters, race organizers, and hazardous-materials- incident
Communications and Reporting System - ACARS - Commercial
aircraft use this packet system to stay in touch in the 129 - 131 Mhz
band. If your TNC is programmed to recognize these packets, they may also
be reported by APRS, giving you position information on all participating
aircraft within 200 miles of your location.
all of this sounds a bit overwhelming to you, remember that our telephone
system in the US is pretty complicated, too, with central offices,
satellite links, switching centers, microwave circuits, cell sites and
much more. BUT it does not take a rocket scientist to make phone call!
Just as a six-year old can effectively use a telephone, a teenager could
easily send and receive messages over APRS.
you can see, there's a whole lot to APRS - more than you could learn in
one sitting. The fundamental concept behind APRS is the old saying,
"A picture is worth a thousand words." The same concept applies
to learning APRS: you could do an awful lot of reading about APRS and
still not have a good idea of how it works. Probably the best way to learn
APRS is to obtain a shareware copy of APRS software for your computer,
load it, and experiment with it. Note that you don't need any radio or
packet equipment to get started. If you can connect to the Internet, you
can see the whole world on APRS!
of typical APRS tracker = http://web.usna.navy.mil/~bruninga/tracker.jpg
a sample screen shot of what the output data might look like, see http://aprs.rutgers.edu/images/NJ.gif
shareware program download site = http://www.cave.org/aprs/
(only those of us on Willit
will need the software, but I mention the link for people who may be
APRS helpers, state by state = http://www.kcaprs.org/elmers.htm.
page of APRS links = http://web.usna.navy.mil/~bruninga/aprs.html
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