APRS.TXT          AUTOMATIC PACKET/POSITION REPORTING SYSTEM (APRS)
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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
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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 has only shown usefulness in passing bulk message traffic 
(Email) from point to point.  It has been difficult to apply conventional 
packet to real time events where information has a very short life time
and needs to get to everyone.

Although the recent interfaces to the Internet make APRS a global 
communications system for live real-time traffic, 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.

     APRS provides universal connectivity to all stations 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 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 CB.txt and CELLULAR.tt.  Now there is even a nation-
wide LIVE APRS tracking network on the Internet!  See APRSnet.txt or
you can connect by Phone line and modem.  See APRStel.txt

APRS is on 144.39 throughout the North American Continent.  Other
countries often use other frequencies.  Check locally.

     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
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 frame
received 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. 

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 those
stations.  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.

For more DF info, see the DF.txt 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.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 can access the worldwide APRServe system in two ways.
First, just hit alt-SETUP-PORTS-MODEM and dial in for an instantanelus
dump of everyone currently on the air.  This will be downloaded to you in
several files.  Just do a FILES-LOAD of any area of the world of interest
and you will see who is on the air.  Using the normal 144.39 channel, you
can send and receive message traffic to ANYONE.

   If you have a text-only type TELNET service, you can use the
APRnet.exe which is a modified version of APRS to join the rapidly 
growing of nationwide linked APRSnet stations.  Just TELNET to Steve's
APRServer at www.aprs.net port 23 and your APRSnet.exe will see over 1000
other stations from all over the country LIVE.  The beauty of APRServe
is that everyone connected, can all FEED their locally heard packets in
to the APRServe system and everyone everywhere can see them...

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 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 10 minutes times the number of digipeater hops
you are using.  This allows the rate to be every 10 minutes for a local
event or every 30 minutes for the typical home station running WIDE3-3.
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:

SCREENS:

  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

SUB-MENUS:

  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

MESSAGES:

  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:

     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
     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.  It
		 can 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
  OTHER FILES:
     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 are
running 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

