README.MOB             TIPS FOR MOBILE APRS USERS


     As a tactical communications system, there is probably no better
application for APRS than in the mobile environment.  One of the greatest
burdens on any public service net, is often traffic involcved with the
location of mobile and portable stations.  Although the use of 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!  For this reason, the first section of this file will
discuss the use of APRS in a vehicle without GPS.


MANUAL POSITION UPDATING:  It can be said that the only stations that need
GPS are the ones that are lost!  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 (IM), 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
county 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
very 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 relatively easy.  First, almost all APRS
commands are single key functions that DO NOT require Ctrl/Alt keys (two
hands!).  The following summarizes all of the commands that are frequently
used in the Mobile environment:

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

    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:  This command is the most important command for manual
        updating of your position.  Simply move the cursor to your position
        and hit I-M.  If all of the other paramters for your station remain
        unchanged, simply hit returns until you hear a BEEP and answer the
        prompt with a Y.  Your position will be updated to the location of
        the cursor.

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-NOgps command below.  Also
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 README.GPS 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.  Once you are interfaced, the GPS
or loran tracking is relatively automatic.  Some useful commands are shown
below:

    Alt-SETUP-TIMEsync - This command will synchronize your PC clock to the
        GPS clock.  THis is important, since APRS will always dead-reckon all
        position reports.  If there is a difference of a minute or more
        between the GPS and the PC, then the PC will automatically compute a
        dead Reckoned posit based on this difference.  Although the distance
        to the DR will be relatively small, on a close-in event like a
        circuitous marathon on the 1 mile scale, these DR plots will be a
        nuisance.  NOTE that this command only synchronizes the minutes, so
        you at least have to be in the right hour....

    Alt-SETUP-POSrate - THis command allows you to set both the periodicity
        that positions are shown on your own display and also the periodicity
        of your position transmissions through the TNC.

    Alt-SETUP-GPS-NOgps - This command allows you to turn off the HSP and GPS
        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 position updating.  If the PC is left in HSP or SPM modes, then
        your local screen will NOT be updated on each DR.  You will only see a
        fresh DR posit each time you hit space bar.  IF HSP and SPM are off,
        then each time your position is transmitted, a new DR plot is drawn.
      

    OPS-COMM-GPS - This command permits you to either communicate with your
        GPS if it has a bi-directional port, or to monitor the data comming
        from your TNC.  In version 5.7b, this command also switched the APRS
        port-splitter circuit so that you could monitor the GPS while in the
        HSP mode. 

