APRS (Automatic Position Reporting System) is a Ham radio digital packet position reporting system. It uses GPS coordinate data from a GPS receiver, sends that data (via a TNC or Terminal Node Controller) to a 2 Meter transmitter, and transmits it in a digital packet radio mode. The frequencies used are commonly 144.34 and 144.39. The data is picked up at a receiving station where the information can be displayed on a computer screen map. When the receiving station is too far away for a direct path, the signal will be picked up by a digital repeater (a digipeater), and retransmitted. There are also gateways set up at receiving stations which relay the digital information to the internet. This means that all that is required to display the data at a computer terminal is either radio reception of the data directly, or access to the internet.

      This system has tremendous usefulness for weather spotting nets. By viewing a computer screen at his desk, the net control operator can instantly see where his spotters are. The info can be superimposed on a radar screen. This saves time for the NC; he doesn’t have to ask you where you are. More accurate reporting is the result. There is also a safety factor here, because the NC can tell a spotter where to go to get out of the way of danger. 

      Implementation in a vehicle can be done a number of ways. The least expensive way is by using an old 2 meter handheld radio (5 watts is more than enough for packet radio, and the duty cycle is extremely low), and hooking that to an inexpensive TNC and GPS receiver. One such device can be found at http://www.byonics.com/tinytrak/tt3plus.php . It costs $108 already built and includes a GPS receiver. A separate 2 meter antenna and you are in business. Many people build an enclosure box, but it is not essential.

       The other (Cadillac) way to implement in a vehicle is with a Kenwood D700. The D700 is a dual band 2 meter/440 mobile radio with a built in TNC. It is all set up for APRS. All you need to add is a GPS receiver. The radio is an excellent one, and can be used for voice modes simultaneously with APRS. Only one antenna is required for both voice and APRS. The drawback to this is that the radio is about $490. But if you are in the market for a dual band mobile radio anyway, I would highly recommend it. You can find this radio listed in the AES catalog at www.aesham.com . 

       If one wants to also receive and display position data of other stations in a vehicle, this can be done also. However, it requires a display unit such as a laptop or a compatible GPS navigation unit with display input. I have only been able to find 2 such suitable GPS navigation units, and they are both expensive. The first is the AvMap GT4 system which can be found at www.avmapnavigation.com , and purchased at AES, www.aesham.com . The second is the Garmin GPSMap 276C. The Garmin unit is a marine plotter and to get street maps you will have to add the automobile kit. Either way, plan on spending around $700-$800. However, the advantage here is that these GPS units are full automobile navigation units which can be used for screen navigation as well as APRS display.