APRtrak.txt                   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 un-protocol 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.


TELEMETRY:

    APRtrak has a simple telemetry decoding and display function
for some very simple balloon and spacecraft payloads.  It can
display 5 analog channels and 5 digital bits of information.  The
primary advantage is that the channel definitions and equations can
be distributed over the air, so that new software is not required
for each different payload.  An exception is for the SPRE payload
scheduled for launch in Dec 95 which has been hard coded.  See
SPRE.txt.  A single chip TELEMETRY/TNC has been designed by
N3MIM which generates AX.25 audio packets with 4 analog channels 
and 5 digital bits.  It makes a great match-box sized balloon payload.


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 CONNECT-REQUEST 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 CONNECT-REQUESTs,
provide much more information, and only required one packet for
success!  

     To demonstrate the effect of having SAREX relay these position
reports, use the FILE-REPLAY 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 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    - The latest UI frame received from each station.
     POSITIONS - Lists the positions of each station. 
     MESSAGES  -  Single line messages to/from other stations.
     BULLETINS - This screen captures all BULLETINS.
     TRAFFIC   - Shows the last 23 lines of messages heard.
     ALL LOG   - Time sequenced log of every new beacon or message.
     HEARD LOG - Number of packets heard per station per hour.  
     DIGIPTRS  - Displays the packet headers and digipeaters used
     TELEMETRY - Displays 5 analog and 5 digital bit channels
     WHERE     - Displays the predicted positions of up to 9 satellites
     AZ/EL (Z) - Shows your antenna's view of the sky
 

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 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 in the same grid
square.  The P-list is annotated to indicate that the position is
approximate.  The big advantage of grid squares is their short
length of 6 characters vice seventeen for lat/long.  You may use 
the OPS-FIND command to locate any grid square on the map.


PROTOCOL - Since the objective of the APRS protocols are the rapid 
dissemination of real-time 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 CONTROLS-XMT command. 
But a transmission can be forced at any time by hitting the X key. 
For details on the APRS raw packet formats see PROTOCOL.txt.

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:

  The Space Bar will always re-draw the map screen and the page
up/dn keys can zoom the map centered on the position of the cursor. 
You may save 4 special maps under the hot keys of 1,3,5,7 and 9.
All of the other displays screens are called up by the letter key
associated with their first letter.  Use alt-T to call up the
TELEMETRY screen.  

SUB-MENUS:

  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 cmds  - Input posits,  or add OBJects to map
  O - OPERATIONS - Several commands for normal operations
  M - MAP Menu   - Functions dealing with maps
   
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 msg traffic between other stations

ANTENNA AZ/EL SCREEN:  The AZ/EL screen is a new screen which shows 
your antenna's eye view of the sky.  You may move the cursor and
zoom into any area of the sky.  The position of the satellites are
shown in real time and their paths can be shown by pressing the alt-F
key for FAST mode.  Use the INPUT-BEAM-heading command to enter the
present position of your antennas.  Enter the Beamwidth of your VHF 
and UHF antennas when you first configure APRtrak on startup.  To 
customize the horizon to your backyard, edit the SYSTEM\HORIZON.dat
file using a simple DOS editor.  The format is described in the
HORIZON.DAT file...  Obviously, this horizon will only show up if
the map screen is centered on your house.  Otherwise, a random horizon
will be drawn.
    

DEMONSTRATION FILE:  To see how APRtrak can display meaningful
packet position reports in a number of different applications,
use FILES-LOAD to load the file called VHF.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.TRK.

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 L-list to hook a
station or object.  Once hooked, several functions may be
performed:

   ALL BCNS- The A key will list all beacons from that station.
   MOVE    - Move cursor and press the Insert key. 
   DELETE  - performed by hitting the D key.
   UPLINK  - transmit the object to all other stations on the net
   KILL    - kill the object from all displays in the network
   ALARM   - You will be alerted if that station ever moves.
   TRACK   - APRS will always center display on selected station
   #MARK   - Mark special stations so that only these stations will
             show on the map when # is used instead of SPACE BAR
             for drawing a map.  If * is pressed, all symbols
             will be shown on the map, but only the marked symbols
             (#) will show callsigns.

The 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.  The G or GO key will go to YOUR station
or if a station is marked for TRACKING on the P-LIST, then it will
go to that station.

REPLAY:  The positions of any 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 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 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 sub-
directories of BAKS, LOGS, HSTS, SYSTEM and README.  There are
several other files used by the system:

  MAPLIST.APR  - Directory of all map files available to APRtrak
  BACKUP  .BK  - 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.
  MAPFIX...EXE - A map editing program for fixing or making maps.
  SYSTEM (DIR) - Contains the following required files
         IintTAPR.TNC - TNC setup parameters  ( or InitAEA.TNC ) 
         RESTORE.TNC  - TNC commands to restore TNC after quiting
         CAPGRIDS.DAT - Civil Air Patrol Search-&-Rescue grids
         DXCALLS.DAT  - Callsign prefix-to-LAT/LONG database
         XXXXxxx.SYS  - Brief files for APRS internal screens
         HORIZON.DAT  - Contains your horizon profile

APRtrak OPERATIONS:

   APRtrak will always monitor the channel and plot any packets or
positions heard.  It will put POSITS on the P-LIST, APRS formatted
Telemetry on the TELEMETRY page, and all other UI frames on the
LATEST list.  The ALL list will keep a chronology of all new
packets and peridoically save them to the LOGS directory.  Unlike
the original APRS software, APRtrak will ignore terrestrial POSITS
from stations that are using more than one digipeater.  The track
history of all positions will periodically be saved to the HSTS
directory.

     There are two TRANSMIT operating modes for APRtrack.  The
nominal mode only transmits your position about once every 10
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 grid-
square 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 GRIDSQ 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 CONGRAT'S
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 XMT-BEACON 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!

*  Set UNPROTO VIA the Space DIgipeater (W5RRR)
*  Set alt-SETUP-MODES-SPACE which makes your posit as short as
possible and also opens up APRtrak to parse all OTHER packets
instead of just APRS packets.  Your station will be "armed" to
reset its beacon timers to minimum as soon as it hears packets from
the space digipeater.
*  Make your BCN text as short as possible, or none at all.
*  Use X command to force a transmission as desired 
*  Use the 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 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 APRtrak unattended, you should capture all POSITS
digipeated by the spacecraft.  Your station will be transmitting
only one BCN and POSIT about once every 15 minutes.  This is less
than one-half 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 you set
SPACE mode, then your station will come to life when the spacecraft
is heard.  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 QRM on the uplink!

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