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   @           LkX@ #| x           2         B                                  APRtrak.doc                   APRtrak

     APRtrak provides a mechanism for plotting the positions of
stations and objects world wide based on both lat/long and grid
square.  It evolved from the APRS (Automatic Packet Reporting
System) software which is a packet program for tracking mobiles
using GPS units interfaced to standard AX.25 packet radios.  The
objective of APRtrak is to provide this same tracking and
plotting capability for Spacecraft and satellite  ground
stations.  Not only does APRtrak satisfy the inherrent curiosity
that all amateur radio operators have about the locations of
other stations, but it also helps newcomers to radio visualize
the three dimensional and geographic aspects of satellite
communications.

     APRtrak is designed to extract the most useful information
for the largest number of users from the minimum number of
packets.  In this respects, it is unlike other packet programs,
because it does not concentrate on the exchange of message text,
but on position data. APRtrak avoids the overhead and complexity
of a connected link by using the AX.25 unnumbered information
(UI) packets.  This mode is called UNPROTO for unprotocol
packets.  These packets are like beacons to everyone on
frequency, instead of being addressed to individual stations. 
APRS scans these UI packets looking for position data or other
useful information in every packet, and only needs one valid
packet to plot a position.

THE SHUTTLE AMATEUR RADIO EXPERIMENT (SAREX):

     The oginal SAREX packet robot was designed in the mid 1980's
when most stations were still using dumb terminals with their
TNC's.  The robot provided unique serial numbers to each station
that connected with the shuttle, but five successful and
successive packets were required for success.  Although hundreds
of stations were successful, more than three times as many showed
up in the HEARD log as having at least gotten one CONNECTREQUEST
packet through.  Thousands more had probably tried.

     APRtrak was designed to take advantage of single packets to
not only permit a greater success rate, but also to provide a
more visually rewarding image of the spacecraft, orbit, and
ground station geometry.   Since shorter
packets result in success of more stations, the complete position
report is compressed into the TO address of all uplinked packets
using the Maidenhead Grid Square system.  These grid squares are
only 6 characters but provide a location anywhere on earth to
about the nearest 2 miles. These position reports then are just
as short as a CONNECTREQUESTs, provide much more information,
and only required one packet for success!  
     To demonstrate the effect of having SAREX relay these
position reports, use the FILEREPLAY command to replay the
SHUTTLE.HST file and watch the contacts appear as the shuttle
moves across the country.  You may enhance the demonstration by   h)        0*0*0*  selecting to see only the Shuttle, STS-99, or by turning off
CALLS to reduce the clutter of callsigns on the display.  
Obviously, in this SHUTTLE.hst file, I assumed that the Shuttle
had its TNC connected to a GPS navigation receiver so that it was
also beaconing its position once per minute.


APRtrak DISPLAYS:

     Obviously the map is the most important display screen, but
APRtrak has several other screens for presenting other
information about all packets that it hears as follows:

     LATEST  This display maintains a copy of the latest UI
frame received from each station.

     POSITIONS  This display maintains a separate list of the
positions of each station often including a brief comment. 

     MESSAGES   Single packets can be addressed to other
stations, but the fact that these messages require a second
acknowledgment packet gives them an order of magnitude lower
success rate.

     BULLETINS  This screen captures all BULLETINS.

     TRAFFIC  This screen shows the last 23 lines of messages
heard.

     ALL LOG  This display is a time sequenced log of every new
beacon or message heard.

     HEARD LOG  This display shows the total number of packets
heard from each station per hour.  

     DIGIPEATER LIST  This displays the raw packet header so
that users can see what digipeater paths are being used by other
stations. 

STATION TRACKING.  Although APRtrak was designed to track
spacecraft and ground station position reports, it can also track
any station, fixed or mobile that is transmitting its position
via packet using the APRS protocols.  Further provision is made
for transmitting the location of objects on one station's screen
to every one else's screen. This feature can be used by one
station to uplink the position of an  artic polar expedition, or
ships at sea for example.

GRID SQUARES:  Because of the ambiguity of a gridsquare 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 in the same grid
square.  The Plist is annotated to indicate that the position is   h)        0*0*0*  approximate.  The big advantage of grid squares is their short
length of 6 characters vice seventeen for lat/long.  


PROTOCOL  Since the objective of the APRS protocols are the
rapid  dissemination of realtime information using packet UI
frames, a  fundamental precept is that old information is less
important than  new information.  All NEW beacons, position
reports, messages and display graphics are redundantly
transmitted but at a longer and longer repition rate.  Each new
beacon is transmitted immediately, then 20 seconds later.  After
every transmission, the period is doubled.  After ten minutes
only six packets have been transmitted.  From then on, only 1
packet every 10 minutes is transmitted.  All transmissions can
be turned off using the CONTROLSXMT command.  But a transmission
can be forced at any time by hitting the X key.  For details on
the APRS raw packet formats see the PROTOCOL.txt file.

COMMANDS:   In most cases the keyboard is always active awaiting
any of the many single key commands.  Many commands bring up
additional menus on the bottom of the screen.  Note that APRS
processing of packets on the air is continuous EXCEPT while
waiting for the user response to a BOXED prompt.  Commands fall
in to 3 categories:

SCREENS:

  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

SUBMENUS:

  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

MESSAGES:
   h)         0*0*0*  Ԍ  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 APRtrak can display meaningful
packet position reports in a number of different applications,
use FILESLOAD to load the file called 2METERS.BK.  This file
contains all the local stations on the local APRS frequency in
the Washington DC area.  To see the tracking of
the GPS equiped Army/Navy game football run, load the 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.

HOOKING STATIONS:  The cursor can be moved to select any station
on the map screens 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.  You may
also use the cursor on the P or Llist to hook a station or
object.  Once hooked, several functions may be performed:

     1.  ALL BEACONS  The A key will list all beacons from that
station.

     2.  MOVE  Move the cursor to a new location and press the
Insert key.      You are then prompted to enter in a new info as
needed.

     3.  DELETE  performed by hitting the D key.

     4.  UPLINK  transmit the object to all other stations on
the net

     5.  QUIT  quit uplinking the object to the net.

     6.  KILL  kill the object from all displays in the network

     7.  ALARM  You will be alerted if that station ever moves.

     8.  TRACK  APRS will always center display on selected
station

     9.  #MARK  Mark special stations so that only these
stations will be      shown on the map when # is used instead of
SPACE BAR for drawing a map.      If the * key is pressed, all
symbols will be shown on the map, but only      the marked
symbols (#) will show callsigns.   h)        0*0*0*  ԌThe hook function also works on the LATEST and POSITION display
lists by using the up/down arrow keys.  If a position exists,
hitting the HOME key will display the map screen with that
station centered on the display.

REPLAY:  The positions of any moving station can be replayed
either from memory or from a file.  Tracks are kept in online
memory until 150 have been saved, and then are saved to a HISTORY
file.  During REPLAY, use the Calls command to toggle on and off
the display of callsigns, 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:

      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 APRtrak files are retained in five different subdirectories of         BAKS, LOGS, HSTS, SYSTEM and README. 
There are several other files         used by the system:

  MAPLIST.sat   The directory of all map files.  APRS uses this
file to find                  out what map to use for a given
cursor location.  Many other                  MAPLIST.xxx files
are now available.   BACKUP  .BK   Automatic backup of system
every time program is quit.  This                  file is
overwritten every time the program is quit.  It can               
  be reloaded by simply indicating the letter B for a filename.  
MAPFIXer.BAS  The Qbasic program I use to fix, draw, and modify
APRS 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.      NWSDATA.DAT   A sample file used to
load National Weather Service data      NWSPOSNS.DAT  A file of
the locations of all NWS sites      CAPGRIDS.DAT  A file of the
Civil Air Patrol Sectional Aeronautical charts     
DXCALLS.DAT   Callsign prefixtoLAT/LONG database for DX spots  
   XXXX.SYS      Numerous brief files for APRS internal screens




APRtrak OPERATIONS:

   There are two operating modes for APRtrack.  The first mode,
or passive mode only transmits your position about once every 10   h)        0*0*0*  minutes.  This position report is your exact LAT/LONG location
and posiiton comments.  It allows all stations on frequency
within range of each other, to see who else is nearby.  The other
mode is SPACE mode specifically designed to transmit a minimum
length gridsquare report via a spacecraft transponder.

   In space mode, APRtrak places your GridSquare in the TO
address of your TNC by using the UNPROTO command of UNPROTO ATRAK
via XXXXX.   Where XXXXX is the callsign of the satellite or
spacecraft digipeater.  If APRtrak sees your packet digipeated by
the spacecraft, it will beep several times and display a
CONGRATULATIONS message.  To imporve your chances for getting a
packet through the spacecraft, you may force a transmission of
your GridSquare BEACON each time your press the XMTBEACON
command.  A timer prevents you from sending an more than one
packet every 8 seconds.  Also in SPACE mode, APRtrak will
automatically increase its beacon rate when ever it hears packets
from the designated spacecraft digipeater.  It does this by
resetting the normal decaying BEACON period timers to minimum. 
This results in several packets over the next few minutes, but,
as usual, the period between each packet doubles.  

To minimize QRM, any APRtrak station that sees itw own BEACON
digipeated by the spacecraft will immediately reset its beacon
timer to 4 minutes, since there is no need for that station to
continue to transmit again until later in the pass to cover a
different geographical footprint.


OPERATING TIPS VIA DIGIPEATING SPACECRAFT:

First, be sure that APRS position reporting is being authorized
via the particular spacecraft.  To have a good chance of being
seen via the SPACE digipeater and to minimize unnecessary QRM,
use the following procedures.  Even under worst case scenarios,
APRS stations will still generate fewer packets than other
stations attempting to CONNECT to the spacecraft!

*  Use UNPROTO to set your VIA path to the Space DIgipeater
(R0MIR or W5RRR) *  Use altSETUPMODESSPACE to make your posit
as short as possible.    This command also opens up APRS to parse
all OTHER packets instead    of just APRS packets.  This way,
your LList will show all stations. *  Make your BCN text as
short as possible, or none at all. *  X command to force a
transmission as desired  OR 
*  Use altSETUPPOSRATE to reset your POSIT period decay timer. 
APRS will    send an immediate packet and then double the period
to the next one and    so forth.  This prevents unattended
stations from accidentally cluttering    the freq.
*  Use the APRS VIEW screen so you can VIEW all packets on a full
screen *  Use your lowest 2m antenna (preferably on the ground). 
This minimizes any    QRM to your receiver from other local
uplink stations, and also minimizes    your QRM to them.  A
ground level antenna should work perfectly well, since    it can   h)        0*0*0*  still see the sky, and the SPACECRAFT is so far away on the
horizon    and has such high doppler that you will NOT make it
anyway at elevations    below 20 degrees or so.


UNATTENDED OPERATION:  If you use a low antenna as described
above and leave APRS unattended, you will be transmitting only
one BCN and POSIT about once every 15 minutes.  This is less than
onehalf of one percent (0.5%) of the number of packets generated
by other stations trying to connect to the spacecraft.  Of course
your chances are similarly diminished, but its only fair for
unattended stations not to QRM manned stations. If this idea
catches on, then maybe all of those other stations will STOP
trying to CONNECT to the spacecraft and join us!  That would be a
net REDUCTION in MIR/SAREX QRM!

    Imagine the fun that the cosmonauts and astronauts will have
if they carry a laptop computer so they can see everyone on
their maps!

NOTE:  Even if you only see a GRIDSQUARE from a station, you can
tell if he is running APRS by the @ vice [ at the start of the
report.  APRS uses this distinction so it can tell who is an online APRS station and one which is only comming from a passive
TNC BText.

