            Using the Wisconsin Network - Part 34
                 by Andy Nemec, KB9ALN

     Over the course of the last few months, we have been
discussing the integration of packet radio into your ARES/RACES
operations. This time out, we will go a little further with a 
discussion of APRS.

     Just what is APRS? It is an acronym meaning "Automated
Position Reporting System". The APRS software allows a station
to broadcast it's position periodically, to receive position
reports from others, and mark it all on a map appearing on your
computer screen. It is all done via packet radio's AX.25
protocol, and most operations take place on 145.790 Mhz.

     In addition to the mapped position appearing on your
screen, APRS software can also broadcast data from some
selected home weather stations. You still can conduct
conversations with APRS, though the process is slightly
different and prone to errors.  

     How does it work? The operator can enter the position
coordinates manually, or a Global Positioning Receiver (GPS)
unit can be added for truly automatic operation. The GPS
receiver listens to signals from several satellites and is able
to calculate it's position relative to the satellites. This
data is displayed, as well as coded and sent to a data output
port. 

     Data from the GPS unit is sent to the TNC, where it is
formatted and broadcasted as a "UI" (connectionless) packets.
Digipeaters are used to relay the signal as required. Some
digis are devoted to localized areas for weak-signal stations,
other digis provide wide-area digipeating, and others act as
HF-to-VHF gateways. They all have specific designations in the
APRS system, and specific functions.

     The software used to interact with the GPS unit and TNC is
specialized and responsible for much of the functionality of
the system. You cannot use a standard terminal program to
operate APRS, it just won't work. The good news is that the
APRS software for DOS, Windows, and MAC formats is widely
available free of charge. You will be pleased to know that
the software does not require a powerhouse of a computer to
run, an 8088 or better is sufficient. The software is also
designed to work with all models of TNC's equipped with APRS.

     What to do with it? Well, the possibilities are plentiful
if you are in the right situation. Think about these for a
moment:

 - Precise position reporting for weather spotting
 - Following a parade route
 - Radio Direction Finding
 - Shadowing Emergency Government personnel

     Any or all of these can help you to do the job better and
faster, not to mention doing things you have never done before.
In short, anytime you need to know where someone or something
is, you can use APRS to report it's position via packet radio.  

     Perhaps by now you have concluded that you can use APRS
and wish to incorporate it into your system. Now you have to
consider what to do in the way of equipment. There are two
approaches here, a traditional and a new method that looks to
be very cost-effective.

     First, the traditional approach. Naturally, you will need
all of the normal elements that comprise a packet station.  The
appropriate radio, antenna, and feedline all have to be there
just as in a "normal" packet station. The TNC must be APRS
compatible, a lot of TNC's of recent manufacture have APRS
support. It is not economically feasible to "retrofit" an old
TNC with current APRS support unless a manufacturer offers a
low-cost kit for a specific model.

     Now you need to think of the GPS unit you will attach to
it. Handheld units are popular for roaming, but suffer from a
little inflexibility. The antennas are built into these units,
and they must have a direct view of the satellites. Permanent
locations can take advantage of a remote antenna installations,
which removes that problem. Most operators select a hand-held
unit for it's portability.

     Once you have decided on the style, you have to do a
little bit of checking before you can determine if it will work
with your TNC. The GPS unit has to send it's data to the TNC,
of course. And it has to have the proper port and data format
for your TNC to understand it. Luckily, this seems to be
somewhat standardized. Most GPS units have the required NEMA
data port with the proper format. If there is any doubt in your
mind as to compatibility, refer to your TNC's owner's manuals
or call the TNC manufacturer. Best to spend the time to check
on this very important matter rather than buy a unit you can't
use! 

     This traditional APRS approach requires a radio, antenna,
TNC, and GPS receiver dedicated to the task. There is another
method of utilizing APRS that may be especially appealing to
Emergency Coordinators for more than one reason.

     This method comes to us in the form of a soon-to-be-
released "semi-kit" from the Tuscon Amateur Packet Radio
Association (TAPR). It is called the "MIC-E" and it allows you
to operate conventionally, yet relay APRS data with your
existing radio. It takes the GPS receiver data, formats it
into a packet, and tacks it onto the end of your voice
transmission. This is a transmit-only system, and does not
require a TNC.  It is intended to plug into the microphone jack
of the radio, with the regular mike plugging into it.

     This is quite an advantage in a number of situations.
There is a much lower cost of equipment, a less complex system,
and the operators have fewer pieces of equipment to fiddle
with. Imagine getting an updated position report from a weather
spotter every time he unkeys his mike - and you can still
utilize existing voice repeaters.

     Those are two ways to implement APRS in your emergency
communications system. If you would like more information on
APRS, try this URL: http://www.macatawa.org/~ares/
It is especially helpful as this is an ARES organization and
use APRS effectively. They also have the current APRS software
for you to download, if you wish.

     There is also the Tuscon Amateur Packet Radio
Association's web site: http://www.tapr.org. This is where you
go for information on the "MIC-E", as well as general
information on APRS.

That's all for this time, until next time 73 from Andy.
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