Automatic Packet/Position Reporting System (APRS)

LIVE APRS web site at

APRS is different from regular packet in two ways. First by adding maps and other data displays, and second by doing all communications using a broadcast protocol so that everyone is updated in real time. APRS turns packet radio into a real-time tactical communications and display system for emergencies and public service applications. Normal packet radio has only shown usefulness in passing bulk message traffic from point to point. It has been difficult to apply conventional packet to real time events where information has a very short life time.

APRS, however, provides universal connectivity to all stations but avoids the complexity and limitations of a connected network. It permits any number of stations to exchange data just like voice users would on a voice net. Any station that has information to contribute simply sends it, and all stations receive it and log it. Secondly, APRS recognizes that one of the greatest real-time needs at any special event or emergency is the tracking of key assets. Where is the Event Leader? Where are the emergency vehicles? Whats the Weather at various points in the County? Where are the power lines down? Where is the head of the parade? Where are the VIP's? Where is the mobile ATV camera? Where is the hurricane? WHERE IS THE DX??? To answer these questions, APRS is a full featured automatic vehicle location and status reporting system too. It can be used over any 2-way radio system including HAM, CB, Marine Band, and Cellular Phone. See CELLULAR.HTM.

Included on the distribution disk are several README text files on applications of APRS such as for weather nets, direction finding, plotting satellite contacts, and monitoring DX clusters. You must read at least the INDEX.HTM, DEMOS.HTM, NEWNOTES.HTM and HELP.HTM files. APRS uses UI frame broadcasts and map displays. There are three major display subsystems and a number of other minor displays as follows:

LATEST STATUS - This display maintains a list of the latest UI frame received from each station. In effect, this is a multi-station one-line broadcast status system. In DX cluster mode, this display accumulates a list of all users and what was their latest command to the cluster.

POSITIONS - This display maintains a separate list of the positions of each station often including a brief comment. They can also contain DF and or WX info. Fixed stations using the ! format will only show on the POSITIONS list and not on any other page unless CONTROLS-FILTERS-!FIXED is toggled off. If FILTER-!FIXED is off, it will show on the upper right of the POSITIONS page. In DX mode, this list contains the posits of all DX spots and user-locations heard.

MAPS - Maps from 300 yards up to 4000 miles can be displayed. All other APRS stations will be plotted. Stations reporting a course and speed are dead-reckoned to their present position. Overlay databases of the locations of all APRS DIGIpeaters, National WX Service sites and even HAM stores are built in. You can zoom in to any point on the globe!

MESSAGES - In addition to the one-line STATUS packets, two-way messages with acknowledgment are supported. All incoming messages alert the user on arrival and are held on the MESSAGE screen until Killed.

BULLETINS - This screen maintains a list of active BULLETINS. These are important multi-line BULLETINS addressed to everyone.

TRAFFIC - Shows the last 23 messages monitored between other stations on the net. DX mode TALK traffic also shows up here. The MAPS-PLOTS- TRAFFIC command will connect these stations with lines on the map.

ALL PACKET LOG - This display is a time sequenced log of every new status or message received. This is in contrast to the LATEST display which only shows the most recent status packet per station. In DX mode, this screen shows all DX/WX/WWV spots and ANNOUNCEMENTS heard.

HEARD LOG - Displays the total number of packets per station per hour. These statistics show the connectivity of the network over varying paths, such as HF, or to see when stations enter and leave the net.

DIGIPEATER LIST - This display displays the raw packet header so that APRS users can see what digipeater paths are being used by other stations. The proper use of digipeaters is important in an APRS network. An asterix in the first column means that you hear the other station direct without a digipeater! Change your UNPROTO path to NONE to chat with those stations. In DX mode, this list accumulates a list of all DX cluster message headers.

STATION TRACKING. Although APRS automatically tracks mobile GPS/LORAN equipped stations, it also tracks perfectly well with manual reports or GridSquares. APRS will use a GridSquare in brackets at the beginning of any packet. Additionally, any station can place an object on his map including himself and within seconds that object appears on all other station displays. In the example of a parade, as each checkpoint with packet comes on line, its position is instantly displayed to all in the net. Whenever a station moves, he just updates his position on his map and that movement is transmitted to all other stations. To track other event assets, only one packet operator needs to monitor voice traffic to hear where things are. As he maintains the positions and movements of all assets 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.

GRID SQUARES: Because of the ambiguity of a grid-square position report, APRS will not display a 4 or 6 digit gridsquare report on map ranges less than 128 and 8 miles respectively. Stations reported in the same grid square are randomly offset to avoid cluttering of callsigns on top of each other. The P-list is annotated to indicate that the position is approximate. It is also very brief; six characters vice seventeen. In GRID-SQUARE mode, APRS will send your posit via GRID SQUARE format vice LAT/LONG. Shortening the packet is an advantage when reporting via HF, Meteor Scatter, SAREX, or the PACSATS.

ACARS: If your TNC has an ACARS modem for receiving Airline digital packets on 131.55 MHz, then the optional APRSair.EXE will plot the positions of all aircraft in range (usually up to about 200 miles out).. See ACARS.HTM

USING APRS ON ALL DIGITAL CHANNELS: If all packet stations on all frequencies would include LAT/LONG or Grid Square in their BTexts, APRS can be used as a general purpose network topology display on ANY packet frequency! See the PROTOCOL.HTM for details on APRS formats and see FRQCOORD.HTM for suggestions for using APRS as a freq-coord display tool.

SPACE APPLICATIONS: APRS is an excellent application for using orbiting packet digipeaters such as on the Shuttle, AO-16, WO-18, LU-19, IO-26 and AO-27. APRS only requires one successful packet for everyone to see each successful station compared to the typical *CONNECTED* SAREX mode which requires 5 successful packets. Not only does APRS reduce channel loading, but it also capitalizes on the most fascinating aspect of the amateur radio hobby, and that is the display on a map of the location of those stations. If everyone simply inserted their LAT/LONG or Grid Square as the first characters of their beacon text, everyone within the satellite footprint would see the location of every successful uplink. Similarly ANY 2m FM rig and ANY TAPR-2 compatible TNC can be used to digipeat APRS packets via any of the PACSATS! See SPACE.HTM.

FOX HUNTING OR DIRECTION FINDING: APRS is an excellent tool for plotting the location of a hidden transmitter, balloon, or interfering signal. APRS has several powerful DF tools:

  1. Plots the positions and Bearing lines of all participating stations whether mobile or fixed
  2. Plots the overlaping signal strength contrours for OMNI-DF reports. This techinque even plots big BLACK circles for NULL reports so that you see all the areas where the FOX is NOT! This OMNI technique is very powerful and locate a jammer to a neighborhood with NO beams or special equipment.
  3. Fade-Circle Search and Rescue technique for single station signal strength location using only a OMNI antenna
  4. Optional automatic DF interface to Doppler DF units for automatic plotting of DF bearings.

For more DF info, see the DF.HTM file.

WEATHER STATION REPORTING: APRS position reports can also include the wind speed and direction, as well as other important weather conditions. APRS supports a serial interface option to the ULTIMETER and DAVIS home weather stations to do this automatically. All weather stations show up as a blue circle, with a line indicating wind speed and direction. The APRS NEXT command will successively highlight each WX station in turn, for WX at a glance. APRS also has a database of the locations of most NWS sites and can crunch a file of NWS hourly WX conditions for display. Finally, APRS users can set WX alarms and be alerted when WX conditions exceed those values. See WX.HTM.

DX CLUSTERS: APRS an ideal tool for the DX cluster user. Not only does he get to see all DX spots on the map, but by operating in the monitor only mode, he has reduced the overall packet load on the DX cluster. This is a benefit to everyone on the channel. Also the APRS monitoring station will see the SPOT as soon as the first station gets it, rather than later on down the list. See DXCLUSTR.HTM.

FREQUENCY COORDINATION: Every packet asset on every frequency should include a position or at least gridsquare in all routine BEACONS. This alows APRS to be used to monitor network topography on any frequency. APRS makes an excellent tool for frequency coordination. The frequency coordinating body can make available APRS backup files (or .HST files) showing the positions of all coordinated services, both packet AND VOICE. These files can be distributed on BBS's to all HAMS in the area. Anyone may then use APRS to view the positions of all packet assets geographically. Also the APRS MAPS-PLOTS-POWER command can plot range contours based on antenna height and gain, for displaying the topology of any network and also the interference ranges of voice repeaters...

PROTOCOL - Although APRS redundantly transmits data, a fundamental precept is that old data is less important than new data. All APRS packets are repeated at an ever decreasing rate. Each new packet is transmitted immediately, then 20 seconds later. After every transmission, the period is doubled. After 20 minutes only six packets have been transmitted. From then on the rate remains at 20 minutes. All transmissions can be toggled off using the CONTROLS-XMT command, or forced at any time with the X key. See PROTOCOL.HTM

COMMANDS: The keyboard is always active. Almost every key does something or brings up additional menus. (APRS processing of packets on the air is continuous EXCEPT while waiting for the user response to a prompt. These prompts are surrounded with a yellow). Commands fall into 3 categories:


Space Key - Display map and all station locations L - Latest beacons - Displays the latest STATUS BEACON from each station P - Positions - Displays a list of all stations reporting positions A - ALL packet log - Keeps a chronological log of all beacons and messages B - BULLETINS - Keeps a list of all BULLETINS heard R - Read Messages - Displays the status of your in and out messages T - Traffic - Displays the last 23 lines of messages between stns D - Digis Used - Displays the digipeater paths being used by others H - Heard Log - Displays packets per hour per station for 24 hours V - VIEW - Displays all packets on a scrolling screen


F1- Help - Select from a 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 - Used to input posits, DF info or add OBJects to map O - OPERATIONS - Several commands for normal operations M - MAP Functions - Functions dealing with maps W - Weather Menu - Displays the number of beacons per hour per station


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

DEMONSTRATION FILE: To see how APRS looks in our area, FILES-LOAD the file named WASHDC.BK. To see the tracking of the GPS equiped Army/Navy game football run, FILES-LOAD FBALL.BK and do a FILES-REPLAY of the file named FBALL93.HST. To see the Marine Corps marathon, load MARATHON.BK and replay the MARTHON.HST file. See Details in README.1st.

HOOKING STATIONS: The cursor can be moved to select any station on the map using the arrow keys. When near any station symbol, the ENTER key will "hook" the station. Detail information on that station will be displayed on the bottom of the screen. Alternatively, use the + and - keys to step through each station one by one. or the <> to step through objects on the current map scale only. You may also use the cursor on the P or L-list to hook a station or object. Once hooked, several functions may be performed:

     ALL    - Displays a list of all beacons from that station.
     EDIT   - Change the position packet text
     MOVE   - Move the station by moving the cursor
     DELETE - Delete the station.
     FOLLOW - Force this object to FOLLOW a course (APRSdr only)
     UPLINK - Toggle on/off transmiting the object to others
     ALARM  - Sets an alarm if that station ever moves.
     TRACK  - Always center display on selected station as it moves
     MARK   - Mark stations for selective display with the JUST command

The hook function also works on the LATEST and POSITION display lists by using the up/down arrow keys.

REPLAY: Replay past track histories either from memory or from a file. Tracks are kept in on-line memory until 150 have been saved, and then are saved to a HISTORY file. During REPLAY, use the following commands:

      C    - CALLsigns on/off
      HOME - Homes map to presently displayed station
      SPACE- Redraws the present map to remove track clutter
      F    - Faster.  Speeds up playback
      G    - Overlays the Civil Air Patrol Search and Rescue grids
      M    - Medium replay speed
      P    - Pause
      S    - Slow.  Slows down playback
      Q    - Quit playback.
      PgUp/PgDn - Zoom in and out

FILES: All APRS files are retained in five different sub-directories of BAKS, LOGS, HSTS, SYSTEM, MAPLISTS and README. There are several other files used by the system:

  MAPLIST.USA  - The file that lists all map files to be used by APRS.  
                 These MAPLISTS are all in the MAPLISTS directory.  Change 
                 to different MAPLISTS using the MAPS-CHANGE command.
  BACKUP  .BK  - Automatic backup of system every time program is quit.  It
                 can be loaded quickly using the FILES-LOAD-B command.
                 Or Automatically by invoking APRSXX/B at the DOS prompt.
  MAPFIX32.EXE - A powerful program for fixing, drawing, and modifying maps!
  SYSTEM (DIR) - Contains the following required files
     IintTAPR.TNC - Setup parameters for your TNC (InitAEA.TNC for AEA)
     RESTORE.TNC  - TNC commands used to restore your TNC after quitting APRS.
     CAPGRIDS.DAT - A file of the CAP Sectional Aeronautical charts
     DXCALLS.DAT  - Callsign prefix-to-LAT/LONG database for DX spots
     XXXX.SYS     - Numerous brief files for APRS internal screens
     METAR.TXT    - A sample file used to load National Weather Service data
     NWSPOSNS.POS - A file of the locations of all NWS sites

CHESSBOARD: To demonstrate the flexibility of APRS in reporting the movement of objects in a net, there is a 2 mile chessboard in the center of the Gulf of Mexico. Two APRS stations can place pieces on the board with the INPUT-ADD command or can move existing pieces using the Cursor, HOOK and INSert commands! An easy way to begin a game, is to load the CHESS.BK file which already has all 32 pieces saved. By selecting the alt-SETUP-OTHER-GAME command APRS not only keeps track of the move numbers but also changes the packet address from APRS to GAME, so that others on frequency will not see their PLists cluttered with the pieces as they are moved. Also, GAME mode only UPLINKS the LATEST move, to minimize QRM. You may consider going to an unused frequency so as not to clutter an active APRS net, however.

If you want to Kibitz a game in progress, also load the CHESS.BK file and use the CONTROLS-FILTERS-OTHER command so that your APRS will monitor OTHER packets on the channel so you will see the GAME packets. If you missed the beginning of the game, ask one of the players to use his P list to HOOK and UPLINK any piece locations you missed.

APRSdr.EXE: For tracking known OBJECTS that move at KNOWN speeds over a KNOWN course, such as the runners in a Marathon, use APRSdr. This program will Dead Reckon objects along the course, so that you can reasonably track the progress of the event, without having to strap a GPS/TNC and RADIO to the head of the lead runner. All GPS mobiles will also be tracked. This is a trememdous visual aid for NET CONTROL.

APRSair.exe: For tracking commercial aircraft using the ACARS system.

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