MOBILE.txt 7.1c           TIPS FOR MOBILE APRS USERS


     As a tactical communications system, there is probably no better
application for APRS than in the mobile environment.  Although APRS on boats
and aircraft which are already equipped with GPS or LORAN is obvious, it is
IMPORTANT TO NOTE THAT APRS IS STILL A VERY USEFUL TOOL FOR VEHICLES WITHOUT
ANY NAVIGATION DEVICE!  Actually, the only stations that need GPS are the
ones that are lost!  For this reason, the first section of this file will
discuss the use of APRS in a vehicle without GPS.


MANUAL POSITION UPDATING:    If a station knows where he is, he just
zooms into his APRS map and moves the cursor to his location.  Then he hits
the INPUT-MYpos command, and his position is instantly updated to that
location.  He is also prompted to enter a new course and speed if it has
changed.  Remember, that once a position has been transmitted, it will be
dead-reckoned on all APRS screens in the network.  This means that as long
as the stations course and speed continue in the same general direction,
everyone on the net will know his position at all times.  Depending on the
speeds involved and the size of the net, updates are only required when
there is a significant change to course and speed.  One station moving cross
country reporting via HF set his course to 270 degrees and set in an average
speed of about 50 MPH.  Although he only updated his exact position once
every few hours, anyone looking at him on the USA map would easily know his
location to the nearest few miles.

   Although we used GPS equipped bicycles during the 1993 Severna Park
marathon, we did not even bother in 1994.  We simply monitored the voice
nets, and occassionally whenever someone mentioned where the LEAD, TAIL or
PACK runners were, the APRS operator simply updated the reported locations,
and all APRS stations along the route could see visualy where these objects
were, even without listening to the radio.  Additionally, since the course
is always known, and the speed of the runners in a marathon is very well
known, the dead-reckoned movement of these symbols between updates was
actually just as accurate as GPS!  Considering the accurracy of GPS is
spec'ed at 100 yards, a quick calculation will show that even an error of 1
MPH in the nominal 9 Kt speed of the lead runner would result in an error of
less than 100 yards in over 5 minutes!   I generally set the LEAD to 9 kts,
the pack to 8 kts and TAIL to 7 kts.  Then later I change the TAIL down to 6
and then 5 MPH as the race goes on.


MOBILE OPERATIONS:  There are several features of APRS that have been
designed to make mobile operations with 1 finger relatively easy.  The 
following summarizes the commands that are frequently used in the Mobile 
environment:

  G - GOTO:  On any screen other than the MAP, this command will redraw 
      the map centered on your vehicle.  If you are already on the map, 
      then GOTO puts the cursor on your station so that a single press of 
      the PgUP/DN keys will allow you to zoom or home the map in one step.

  T - TRACK:  This command is available once you have hooked a station on
      the P-list.  It allows you to designate any station for autotrack.
      As a tracked station approaches the edge of any map, APRS will
      automatically re-draw the map in that direction.  If TRACK mode is
      on, then the GOTO command will go to the Tracked vehicle.

  A - ALARM:  This command, also on the P-list, allows  you to set an alarm
      on any station.  If it moves, an alarm goes off, and your screen is
      immediately centered on the station.  I use this one in my shack a lot
      when my wife is using the car and I need to know when to look busy and
      domestic on her return.

  IM - INPUT-MYpos:  To manually update your position, simply move the cursor
      to your positionand hit I-M.  If all of the other paramters for your
      station remain unchanged, simply hit ENTERs until you hear a BEEP and
      answer the prompt with a Y.  Everyone will see you at the new position.

Unless your exact location between point A and B is important, simply enter
your estimated average speed, and the straight line course to B.  This way,
other stations will be able to see your dead-reckoned progress toward B and
you will not have to make frequent updates.  Since APRS also DR's your
progress on your own screen, you will see the same thing that everyone else
sees.  You can tell whether you need to update your progress or not.  You
will notice, that on your own screen, each DR'ed position is posted at the
same time that a position report is transmitted by your station.  That is
why the reports will be close together initially and be spaced further and
further appart.  In order for this DR to work on your own screen, you must
not be in HSP or SPM modes.  See the ALT-SETUP-GPS-OFFgps command below.  
If you want to see where your DR'ed position is at any time between transmis-
sions, simply hit the space bar, and a fresh DR will be displayed.


AUTOMATIC GPS/LORAN INTERFACES


    See the GPS.txt file for information on interfacing your PC to GPS
or LORAN.  There are several methods of interfacing depending on whether
you have a dual or single port laptop, and whether your GPS/LORAN has a
periodicity that is user programmable.  Some useful commands are:

    Alt-SETUP-GPS-TIMEsync - Synchronizes your PC clock to the GPS time
        in the next GPS posit heard.  This is important to avoid dead-
        reckoning errors on small area maps!
        NOTE that this command only synchronizes the minutes, so
        you at least have to be in the right hour....

    Alt-SETUP-POSrate - Allows you to set both your own screen updates and
        the on-air transmission rates through the TNC.

    Alt-SETUP-GPS-OFFgps - Allows you to turn off the HSP/SPM modes without
        having to re-configure.  This is necessary if you are normally
        configured for HSP or SPM modes but are going to be doing manual
        updating.  If the PC is left in HSP or SPM modes, then your local
        screen will NOT be updated on each DR.   IF HSP and SPM are off,
        then each time your position is transmitted, a new DR plot is drawn.
    

    OPS-COMM-GPS - Permits you to either communicate with your GPS if it has
        a bi-directional port, or to monitor the TNC.  This command also
        switches the APRS port-splitter circuit in HSP mode so that you could
        monitor the GPS.

    F6  This key is called the QRT function.  When QRT is set, your station
        will always set your SPEED to zero.  This is so as you approach 
        your destination, you can send several 0 speed posits to prevent
        everyone's screens from DRing you forever when you go QRT.
