Automatic Position Reporting System

(APRS) AUTOMATIC POSITION REPORTING SYSTEM
APRS is a program that uses inexpensive GPS receivers to display the locations of moving cars, vessels, aircraft, etc. stations on your computer. By using any radio network with a radio data modem (about $170), all stations can see the movements of all other stations. APRS permits any number of stations to exchange data just like voice users but without the complexity of maintaining separate point-to-point links. The primary APRS display screen is the MAP display. To help mobile units find each other, there are radio nets standardizing on several radio channels:

VHF-FM (HAM) 144.390 Mhz

APRS accomplishes one of the greatest real-time needs at any emergency, or activity, the tracking of important assets:

• Where is the lead vessel / car / aircraft?
• Where are the emergency vehicles?
• What's the Weather at critical locations?
• What is the location of a water pump?
• Where are the Mayor, President, other VIP's, in a parade?
• Where is the Emergency Operations Center?
• Where is there a remote TV camera?
• Where is the search area, gas dock, oil spill, etc?
• WHERE ARE OUR UNITS?

The shareware program has many README.txt, text files on applications of APRS such as for weather nets, direction finding, plotting satellite contacts, and tracking facilities. In addition to the map display from any range from .5 to 4000 miles, there are several other screens:

• LATEST LIST - Latest STATUS beacon from each station
• POSITIONS - Posits
• MESSAGES - Operator-to-operator messages
• BULLETINS - BULLETINs (ANNOUNCEMENTS)
• TRAFFIC - 23 lines, messages from ALL stations
• ALL LOG - Time sequenced log of new beacons or messages
• HEARD LOG - 24 hour record of who is on the air
• DIGIPEATERS - List of relay points (digipeaters) used

STATION TRACKING. APRS automatically tracks mobile stations interfaced to GPS or LORAN navigation, it also easily tracks manual reports. A station can place an object on his map including his station and within seconds that object appears on all other displays. For example with of a parade, as each checkpoint comes on the air, its position is instantly displayed to all in the net. When a station moves, he updates his position on his map and that movement is transmitted to all stations. To track other event assets, an operator can simply maintain the positions and movements of the facilities on his screen, all other displays running APRS software display the same displays. There is also a Tracking command on the P display that will cause APRS to keep the map display always centered on a selected object.

SPACE APPLICATIONS: Some HAM radio satellites may not only transmit their current location, but can also be used for relaying station position reports between ground stations over large areas. The value of the map displays are in their ability to help students visualize the three dimensional geometry of an overhead pass.

FOX HUNTING OR DIRECTION FINDING: APRS is an outstanding tool to plot the location of a hidden transmitter, balloon, or interfering signal. APRS will display the intersection of bearing lines from several reporting stations and also overlapping signal strength contours if only signal strengths are reported. Also, APRS includes a Fade-Circle Search and Rescue technique which can be used by a mobile with only an OMNI antenna to locate a hidden transmitter.

WEATHER STATION REPORTING: APRS can position reports that include direction of the wind, and its speed, also important weather details. APRS supports a serial interface option to the ULTIMETER-II home weather station. With this interface, your station includes Weather in position reports for display at other stations in the network and you appear as a bright blue circle, with a line indicating wind speed and direction.

FREQUENCY COORDINATION: As more and more digital devices include APRS position information in their routine BEACONS, APRS makes an excellent tool for displaying the topology of radio networks as an aid to frequency coordination.

PROTOCOL - To most efficiently use a radio channel, APRS assumes that old information is less important than new. Therefore, all packets are redundantly transmitted but at a longer and longer repetition rate. Each new packet is transmitted immediately, then 10 seconds later. After every transmission, the period is doubled. After ten minutes only six packets have been transmitted, and they stabilize to once every 10 minutes beyond that.

COMMANDS: The keyboard is always active for over a hundred different commands. Aside from selecting the displays shown above, and manipulating the map display, there are several other sub-menu commands and the message commands:

• F1- Help - MENU of HELP commands
• C - Controls - Display a one line status of all control states
• F - FILES Menu - For Loading/Saving files, or Replaying tracks
• I - Input commands - To input posits, DF info or add OBJects to map
• O - OPERATIONS - Commands for normal operations
• M - MAP Functions - Map functions
• W - Weather Menu - Number of beacons per hour per station

• R - READ - Displays your incoming and outgoing messages
• S - Send - Sends traffic to a station
• E - Erase - Erases outgoing traffic lines
• K - Kill - Kills incoming traffic lines
• T - Traffic - Displays message traffic between other stations

DEMONSTRATION mode: See how APRS works on a frequency, use FILES-LOAD to load the file called FREQ579.BK. This file contains all the local stations. To see the tracking of the GPS equipped Army/Navy game football run, load a file named FBALL.BK and replay the file named FBALL.HST and select to see only FBALL, or CHASE1. To see the Marine Corps marathon event, load MARATHON.BK and replay the MARTHON.HST file. See Details in README.1st.

REPLAY: The positions of moving station can be replayed either from memory or from a file. Tracks are kept in on-line memory until 150 have been saved, and then are saved in a HISTORY file. During REPLAY, use the Calls command to toggle on and off the display of call signs, and use the HOME and page keys to center and zoom the map display if the mobile station moves off the screen. During replay, use these commands:

FINDING A COPY OF APRS: The latest version (updated often) of APRS can be downloaded at the top of this page or found on many Amateur radio bulletin board systems. All you need is the APRSxx.zip file and the regional map file for your area, either E, C, W, or SEmapsXX.zip. You can make your own maps, find more local maps at websites for your state, such as WA, OR, MT, ID, IL, IA, and MOmapsxx.zip. After creating an APRS directory, be sure to use PKUNZIP -d. The -d option assures that the complete APRS directory structure is re-constructed as you unzip the files.

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