This project is about building a APRS tracking device. APRS stands for automatic packet reporting system. APRS is commonly mistaken as automatic position reporting system, but its not. The APRS System was developed to provide immediate local digital and graphical information. This includes not only tracking and monitoring position information, but also status, messaging, and bulletins. APRS is not only available in America but around the world. Anybody can use APRS as long as they have an amateur radio license.
In 1984 Bob Bruninga invented APRS. APRS was not officially released to the public until 1991 though. He created APRS on an Apple II computer. Now APRS consists of a very large land based wireless network with almost 30,000 users around the world.
APRS usually works with a GPS, which gets data from at least four different satellites orbiting earth. Then through the protocol made by the National Marine Electronics Association or NMEA for short it goes to a terminal node controller or TNC for short. After the information goes into the TNC, audio comes out in the form of packet APRS. The packet radio is in the form of little bursts of tone, which to us sounds like static. These packet bursts corresponds to ones and zeros. Next it goes into a two-meter radio, which transmits it on a certain frequency. This frequency is 144.39 megahertz. The transmission will go to another two-meter radio somewhere else. Then that radio sends the packet bursts to another TNC. Then the TNC is connected to a computer. The data goes into the computer and it sends it into the Internet. The TNC could also be connected to weather station gear. If it is, then it will send the weather information along with all of the other information. If it is not connected to the Internet it will re-transmit the data until it gets to a computer that is connected to the Internet. From there we access it from our home computer that will display the position on a map.
A global positioning system or, more commonly known as, a GPS works by using satellites. There are twenty-four GPS satellites orbiting earth at an altitude of about one thousand, one hundred miles in the air. There are always six or seven satellites overhead at all times. For a GPS to work it needs to be in line of sight with at least 3 of the satellites. The GPS system actually does some trigonometry.
Basically how it works is that if you intersect two spheres you get a circle.
If you intersect three spheres you get two points.
The earth acts as a fourth sphere, which pinpoints your location.
The APRS signal can travel by many different ways. One example is direct relays. Direct relays are basically from a house to a house or from a house to a car.
(For the next bunch of diagrams we are the blue van, the green star is a digipeater, and the diamond with the “G” in it represents the Internet Gateway.)
Then there are also relays and digipeaters. A digipeater is like a big antenna that transmits the signal much more powerfully. Digipeaters are usually located high up on the mountains. So a relay and the digipeater is if you cannot reach the digipeater so you go through a different house or car first and they automatically transmit it to the digipeater. The digipeaters then broadcast the signal everywhere until it finds a house connected to the Internet.
If you can reach the digipeater you can go directly to it. This is going strait though the digipeaters.
Sometimes you will have to do multiple hops where it goes to a digipeater then gets re-transmitted to a house then another and another until one of them is finally connected to the Internet.
Sometimes if your lucky, the digipeater will be connected to the Internet and all you have to do is get it to the digipeater and it does not need to re-transmit it to a place with Internet.
APRS has many different uses and applications. For example if the tracking device is small enough it can be placed on a rescue dog’s collar and when the dog goes out after an avalanche, or another major catastrophe like an earthquake, you can see where the dog or dogs are at all times. This way after the dog goes out and you still cannot find the people that are in danger, you can see where you have been and where you have not. This way you can go to the places where you have not been and save the person or people that need help. Another use for an APRS tracker is you can put it in a model rocket. This is useful because if the tracking device it connected to a GPS you can also measure altitude.
It would also be good in a model rocket because if the model rocket goes off course you can track it and figure out where it landed. Usually the rocket would just be lost forever but with the tracker inside it you can retrieve it instead of just losing it. It can also be used in an emergency. You can put a tracker on all of the emergency vehicles and see where they are. Another very useful use for an APRS tracker is that police can tag a run away vehicle. Instead of having a high-speed chase that can cause accidents, the police can put a tracker on the car and just find the criminal later. This is a more efficient way because this way no one else gets harmed in an accident because of a chase. Also it can be used at a school. They can put a tracking device on the school bus so they can see where the bus or busses are at all times so they know if is late or stuck in traffic. If it is late or stuck in traffic they can even so how far away it is. Say a little toddler keeps escaping from the house and goes somewhere else all the time you can just slip a tracking device in his pocket and whenever he runs away you can just track him. This is much more efficient because instead of wasting time searching for hours looking for him you can just look it up and find out exactly where he or she is. Another use for an APRS tracking device is to put it on a satellite. This way you can see where in the orbit the satellite is. You would also be able to see how what altitude the satellite is at. Another very common use for APRS is actually not for tracking but for weather purposes. Instead of having position information be displayed it can have weather information be displayed. All someone needs to do is instead of having a GPS connected you have some simple weather supplies such as a thermometer, a rain gauge, and a wind gauge connected to the TNC. This way it will display all of the weather information instead of the position.
In summary, APRS was invented by Bob Bruninga in 1984. APRS works by using a TNC and a computer and usually a GPS. APRS is very useful in so many different ways.
Work Cited Page
Bob Bruninga, 1999. 2 Nov. 2007 <http://web.usna.navy.mil/~bruninga/APRS-docs/ARTICLES.TXT>.
The ARRL Extra Class License Manual. Newington, CT: ARRL, 2002.