A P R S
Automatic Packet Reporting System (APRS) is an amateur radio-based system for real time tactical digital communications of information of immediate value in the local area. In addition, all such data is ingested into the APRS Internet system (APRS-IS) and distributed globally for ubiquitous and immediate access. Along with messages, alerts, announcements and bulletins, the most visible aspect of APRS is its map display. Anyone may place any object or information on his or her map, and it is distributed to all maps of all users in the local RF network or monitoring the area via the Internet. Any station, radio or object that has an attached GPS is automatically tracked. Other prominent map features are weather stations, alerts and objects and other map-related amateur radio volunteer activities including Search and Rescue and signal direction finding.
APRS has been developed since the late 1980s by Bob Bruninga, callsign WB4APR, currently a senior research engineer at the United States Naval Academy. He still maintains the main APRS website. The acronym "APRS" was derived from his callsign.
Click the Car
AUTOMATIC PACKET/POSITION REPORTING SYSTEM (APRS)
Document version: 8.5.3 (10 year anniversary update)
Document dated: 18 Sept 2002 (Previous version was 1 Mar 2000)
Author(s): Bob Bruninga, WB4APR@amsat.org
Home page: www.aprs.org or www.ew.usna.edu/~bruninga/aprs.html
APRS is a real-time tactical digital communicatons protocol for exchanging information between a large number of stations covering a large (local) area. As a multi-user data network, it is quite different from conventional packet radio.
APRS is different from regular packet in four ways. First by the integration of maps and other data displays to organize and display data, second, by using a one-to-many protocol to update everyone in real time, third, by using generic digipeating so that prior knowledge of the network is not required, AND FORTH, since 1997, a worldwide transparent
internet backbone, linking everyone worldwide. APRS turns packet radio into a real-time tactical communications and display system for emergencies and public service applications (and global communications). Normal packet radio is useful in passing bulk message traffic (Email) from point-to-point, but it does not do well at real time events where information
has a very short life time and needs to get to everyone quickly.
APRS is a LOCAL RF network. Although the Internet monitors APRS worldwide,this is not the primary objective. But like all of our other radios, how we use APRS in an emergency of special event is what drives the design of the APRS protocol. Although APRS is used 99% of the time over great distances, and benign conditions, the protocol is designed to be optimized
for short distance real-time crisis operations on RF.
APRS provides universal connectivity to all stations in the net by avoiding 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?
To answer these questions, APRS transmits and captures the location and status of all stations. It can be used over any 2-way radio system including HAM, CB, Marine Band, etc. See CB.txt, Boats.txt, Aircraft.txt.
APRS is on 144.39 throughout the North American Continent. Other countries may use other frequencies. Check locally.
Included on the original APRSdos distribution disk (and this web site), 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 README.1st, DEMOS.txt, NewNotes.txt and HELP.txt files. APRS uses UI frame broadcasts and map displays. There are three major display subsystems and a number of other minor displays as follows:
LIST-STATUS - This display maintains a list of the latest UI status packet from each station. In effect, this is a multi-station one-line broadcast status system. On a DX cluster freq, 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.
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 42 messages monitored between other stations on the net. The MAPS-PLOTS-TRAFFIC command will connect these stations with lines on the map.
LIST-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.
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.
ANALYZE - This display is a great tool for monitoring the APRS local network and giving selected displays on numerous statistics abotu the local RF network. Just digipeaters, Just mobiles, Just WX, selection by software version, object type, or a display of the number of hops used by each station and digi.
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. Grid Squares are brief; six characters vice seventeen. APRS uses this to advantage in GRID-SQUARE mode, for 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.txt
USING APRS ON ALL DIGITAL CHANNELS: Use APRS posit packets on all frequencies as a general purpose network topology display on ANY packet frequency! See the PROTOCOL.txt for details on APRS formats and see FRQCOORD.txt for suggestions for using APRS as a freq-coord display tool.
SATELLITES: Use the special version APRStk.exe to enjoy APRS and also see all the satellites when they come in view. At least 5 satellties permit APRS digipeating and 7 can be received by your Kenwood Radios and auto-tuned by APRStk for each pass! APRS is ideal for the short but congested satellite pass. 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. Thus APRS reduces channel loading, while capitalizing on the most fascinating aspect of the amateur radio hobby, and that is the display on a map of the location of thosestations. See SPACE.txt.
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.
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.txt.
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.txt.
INTERNET: APRSdos no longer supports the APRS-Internet access, since it is now just too big. And APRS is a local RF network anyway for most local practical applications.
Other APRS clients will attempt to display the 30,000 or os other APRS stations worldwide, though this can be flitered as needed to cut the clutter. The real beauty of APRS-Internet system is that is gives long distance connectivity automatically to APRS MESSAGES. All packets everywhere go IN to the APRS-IS, and if needed, any station-to-station messages go out the other end on RF to another user.
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.Thus, APRS makes an excellent tool for frequency coordination. In fact,
javAPRS is now used by TAPR to maintain the entire digital data base for North America.
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 10 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 10 minutes for local 1-hop nets and every 30 minutes for stations using 2 or more hops. All transmissions can be toggled off using the CONTROLS-XMT command, or forced at any time with the X key. See PROTOCOL.txt
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 - LIST - Menu for DX, LOG, TELEMETRY, RESOURCES screens
P - Positions - Displays a list of all stations reporting positions
B - BULLETINS - Keeps a list of all BULLETINS heard
R - Read Messages - Displays all 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 control panel
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.
SELECTING 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 "select" 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 select a station or object. Once sselected, several functions may be performed:
LAL - 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
SPECIAL- Mark stations for selective display with the JUST command
The select 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. Itcan be loaded quickly using the FILES-LOAD-B command.Or Automatically by invoking APRSXX/B at the DOS prompt.
MAPFIX40.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,
SELECT 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 SELECT and UPLINK any piece locations you missed.
OTHER SPECIALIZED VERSIONS OF APRSdos:
APRSmax.exe This program removes some rare features from the full up APRSdos to make more room for more stations. This version will capture and display over 250 stations compared to the original 100. When either system is full, the oldest station is deleted to make room for each new station heard.
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.
APRSwx.exe: This version minimizes serial port overflow if you arerunning an interface to an Ultimeter 2000 WX station.
APRSmin.exe: This version runs in less space, about 450K instead of 550.
APRSair.exe: For tracking commercial aircraft using the ACARS system.
APRSnet.exe: For tracking all packets on the INTERNET www.aprs.net:10151
APRStk.exe: Includes Satellite tracking and Kenwood radio tuning
APRSdata.exe: A local tiny-web-page server for all mobile kenwoods
One of the best APRS programs available with internal maps.
And the original APRS programs.
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