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APRS - Automatic Position Reporting System
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An increasing number of radio amateurs are using APRS to broadcast
his or her current position, or to read that of other hams. APRS
can be implemented rather easily and most of the components needed,
can be obtained from the 2nd hand market. Generally speaking, the
following components are required:
- GPS antenna
- GPS receiver
- Mobile transceiver (2m or 70cm)
- Modem (e.g. TinyTrack)
The first thing you need is a (free) rig that can be used exclusively
for APRS (i.e. not used for phone at the same time). Museum Jan Corver
is currently selling surplus Bosch KF161 mobile transceivers that are
ideal for this application and are also very cheap. Please follow
the link below to find out how you can obtain one of those rigs.
Next you need a modem capable of transmitting and receiving the required
data in the standard AX25 protocol. This is the same protocol as is used
for Packet Radio. One such modem is the famouse TinyTrack design, that
is available as a DIY kit on the Internet (please follow the link below
for more information),
Fixed stations (e.g. your home) are now more or less ready, as they
can 'program' their fixed position in the modem. Mobile stations however,
will need a suitable GPS receiver and GPS antenna, in order to obtain
their position.
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This block diagram shows what is needed for an active APRS station.
To the left is the GPS antenna that will receive signals from a number
of statellites simultaneously. It is important that this antenna has a
clear view, so that it can 'see' a larger number of satellites. The
more satellites it sees, the more acurate it will calculate your
position.
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The (active) antenna amplifies the signals and passes them on to the
GPS receiver. The receiver compares the various signals and calculates
your position with a high accuracy. Once the position is calculated,
it is passed on to the modem in the so called NMEA format. The modem
then broadcasts the position in the 2m or 70cm band, unsing the AX25
protocol.
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When using a GPS receive you'll need, of course, a suitable antenna.
Although it is perfectly possible to build your own (passive) antenna,
it is advised to use a commercially available active one. Such active
antennas are often quite small, can be mounted easily on the roof of
your car, and feature a very high gain.
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Museum Jan Corver has a limited number of brand new Trimble GPS antennas
available for sale, at a greatly reduced price.. These active antennas
are fed by a 5V power supply over the thin coax that is molded to the
unit. The Trimble antenna can be connected directly to e.g. the well
known Lassen II receiver (see below).
 Price list
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Many suitable GPS receivers are available on the 2nd hand market. Some
are smaller than others, and some need minor modifications before they
can be used. One very suitable receiver is the Trimble Lassen-II that
is available as a plug-in unit (often found as surplus part of a taxi
meter). The module can be connected directly to the Trimble GPS antenna
described above and the NMEA data is available on its RS232 port that
can be connected directly to the modem (e.g. TinyTrack).
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A modem is used to link the GPS receiver to your 2m or 70cm transceiver.
The digital information produced by the GPS receiver is converted by the
modem into the well known AX25 protocol that is also used for Packet Radio.
TinyTrack is a very small APRS interface that can be build into most rigs
without too much hassle. The modem is build around a PIC microcontroller
and links the rig to the GPS receiver (and optionally a PC). Please note
that TinyTrack is a very simple modem that only implements part of the
AX25 protocol. For this reason, TinyTrack is only suitable for broadcasting
your current position and not for the reception of the position of the
position of other hams. In othe words: TinyTrack is uni-directional. If
you want to receive APRS information, you'll need to find another solution
(see below).
MOre information about TinyTrak
DOS configuration for TinyTrak
Mac configuration for TinyTrak
MIC-E version of TinyTrack
TinyTrack is available as a bare PCB, a DIY-kit or as a readily build unit.
Museum Jan Corver is currently considering to make a TinyTrack compatible
unit available as a DIY kit. If you are interested in such a DIY-kit,
please drop u an e-mail at the address below.
Yes, I am interested in a DIY-kit
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If you want to be able to receive and broadcast APRS data permanently,
you are advised to make a 2m or 70cm rig exclusively available for this
purpose. As the APRS frequencies are fixed for both amateur bands, you
don't need any fancy features on the rig. Museum Jan Corver has some
very suitable portable and mobile transceivers available for this purpose.
In particular the 2nd hand Bosch KF161 is very suitable for this application
and the museum has many of these units available that are already equipped
with the correct cristal.
Bosch KF161 APRS mobile transceiver
AEG Teleport 9 portable transceiver
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Receiving APRS through the sound card of your PC
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If you have a PC with a suitable sound card available, you may be able
to use it for the reception of APRS signals, using only a few external
components. PA7PTT and PA7FL have created some guidlines that will
help you to connect a Bosch KF161 to your PC in just 10 steps.
Using the sound card of a PC for APRS reception
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Special software is available to display the location of many APRS
stations on your PC (see below). If you have access to the Internet,
you might want to check the location of a known amateur at http://www.findu.com
Just as an example, you may want to click the following link to find
the location of Museum Jan Corver
in The Netherlands. Within a few seconds, a map will be displayed, showing
the latest known position of the requested station. Such links can be added
to your website easily, by creating a link to:
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http://www.findu.com/cgi-bin/find.cgi?pa0vyl
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Replace the call-sign (pa0vyl in the example above) by your own
call-sign. When a visitor on your website clicks the link, a
request will be sent to the findu server (pronouce: find-you).
The server will then try to locate the requested station for you.
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A lot of useful software is available if you want to display maps
and APRS data on your PC. Which program is suitable for you, depends
on the type of PC and the operating system you are using. Here
are some links to help you find your way:
PocketAPRS
APRS/CE
UI-View
XASTIR
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Many maps, suitable for APRS use, are available on the Internet.
Please note that the file format of these maps can be different
for the various operating systems around. So, before downloading
files, please check first if they are suitable for your system and
your software.
Generally speaking, two types of maps are available: bitmap images
and vector images. The first kind (bitmap) is the most commonly used
and will be suitable for most applications. THe graphical quality
is reasonable good but, due to the nature of bitmaps, they are not
suitable for zooming in and out. If you want to be able to zoom in
and out at will, please look for vector images. With the latter,
the entire map is recalculated and redrawn each time you zoom in
or out, without loss of quality.
Maps
More maps
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