APRS

APRS stands for Automatic Position Reporting System.  By using a global position satellite (GPS) receiver and a suitable radio transmitter a location can be transmitted and received at a remote site.  Raynet use this in order to track the location of mobile operators on incidents.  For example if we are out with a search party, on a wide area search, the control centre need to know where that search party is at all times.

On events such as a long distance bike ride, over say 40 miles, the control centre need to know where the back of the ride is.  It is usual to have one or more sweep vehicles collecting broken bikes or injured riders.  Knowing where these sweep vehicles are at all times helps in placing them where they are most needed.

The mobile equipment needed for this is relatively simple.  A suitable radio, a GPS receiver and an interface between the two.  Some radios have this interface, known as a TNC, built in.  The most well known and used are two from Kenwood, the TM-D700 and the TH-D7.  The latter is a handheld unit while the former is for permanent installation in a vehicle.

In the control centre (Control) there will be a computer, often a laptop, a suitable radio receiver and a TNC interfacing between the two.  The computer will have a program that converts the incoming data, from the receiver, into a position that is plotted on a map.  The most used program is Ui-view.  There are two versions of this program a 16 bit version and a 32 bit version.  The link on the side bar will take you to the Ui-view program site.

Instead of using a TNC (terminal node controller) as the interface you can use software and feed the output from the receiver into the sound card of the computer.  The program is AGW Packet Engine, AGWPE for short.  There are two versions of this program, a free simple version and the Pro version with more facilities.  The link on the side bar will take you to the AGW web site.

In order to make best use of APRS you need to be able to create suitable maps.  If the area to be covered is quite small it is best to make a map that only covers the area in use.  I use AutoRoute 2006 to make my maps, it is quite complicated!  To make suitable maps you also need a graphics program such as Paint Shop Pro or Adobe PhotoShop.  I use the former.

The procedure is to open AutoRoute and zoom into the area required.  Then open Location Sensor.  Place the cursor as close to the top left hand corner of the map as possible and note the latitude and longitude given in the location sensor.  Then move the cursor to the bottom right hand corner and again note the latitude and longitude readings.

Save the map to the clipboard.  This can be done on the EDIT menu or by using ctrl C.  Open your graphics programs and paste the map into the graphics program.  Save the map as a .PNG file.

Now comes the tricky bit!  You have to make an information file for Ui-view to read.  To automate this as much as possible I have written a utility to do this for you.  If you would like a copy of this file please email me here and I will forward a copy.