CAP.txt 6.4a               CIVIL AIR PATROL and APRS

FOR DETAILS, CONTACT THE ARIZONA WING OF THE CAP which is doing performance
testing on the APRS system.

SAR GRIDS:  APRS can overlay the 15x15 minute Search & Rescue (SAR) grids
used by the CAP.  Although this is a national grid system based on the USA
sectional aeronautical charts, it also correlates exactly with the outlines
of the readily available USGS 7.5 minute maps.  These grid squares are well
numbered within each sectional chart.  The problem of overlaps are resolved
by defining the western most map to always take precedence.  APRS accomplishes
this ordering by the sequence of maps listed in the CAPGRID.DAT file.  Also,
the ALBUGUERQUE map must be the first one (APRS uses that to know if the file
has been loaded).  Except for the overlaps, most charts are listed
alphabetically.

The numbering plan displayed by APRS is determined by the exact location of
the cursor.  If the cursor is in an overlap area, the proper grid numbers will
be seen.  If you are just to the side of the overlap area, then APRS will
use the numbering scheme that applies to the exact grid found at the cursor.
This may place the "wrong" numbers in the adjacent overlap area temporarily.

TO DISPLAY CAP GRIDS, USE THE MAPS-PLOTS-CAP COMMAND.

There are several ways to determine if you are in an overlap area and if you
are getting the correct numbers.  1) zoom up to where you can see the
sectional chart boundaries (yellow).  Any overlap areas whould be obvious.
2) be sure that your cursor is in the overlap area and re-display the
grids.  3) on each new screen re-display the grids and for areas that are not
numbered, move your cursor to the west and re-display again.  This way, the
western numbers will always overwrite with the correct numbers.


TRACK HISTORIES:  Back at the SAR headquarters, complete track histories can
be processed offline from the main APRS Communications computer.  Periodically
the main APRS computer should do a FILES-SAVE to save the latest track history
to file.  Then he should do a FILES-DOS to shell to DOS and copy the latest
track history file from the HSTS sub directory onto a floppy disk.  This disk
can then be taken to another computer for analysis and the APRS computer can
EXIT back into APRS without loosing anything.  APRS maintains a 2k comm
buffer, so even if the packet channel is continuing to operate at full
capacity, you have a total time of at least 40 seconds before you begin to
loose data.  APRS will automatically do a save to disk whenever 199 positions
have been received.  After all saves, memory is cleared except for the last
position of all stations.

BEACON PERIOD:  At the request of the Arizona section, I have added the ability
for the user to set his maximum beacon period to a few hours vice the normal
default of 15 minutes.  This would reduce the number of UI frames on their
shared packet channel.  To do this, the user must modify the Decay time using
a text editor on the CFIGxxx.xxx file found in their root directory and
change the value to something other than 750.  I do not feel that this is
necessary or advisable.

  1)  It defeats the real-time objective of APRS to maintain knowledge of
  the activity of all stations on the net.

  2)  The channel time used up by in-active APRS stations is less than 0.2%
  each.  Ten such stations would use only 2% of channel capacity.

  3)  Each station can simply use the CONTROLS-XMTR-OFF command to silence
  APRS (it will still respond to incomming messages)

Another solution for stations bothered by APRS beacons, is to set the call
of APRS in the LCALLS list of their TNC's and set BUDLIST OFF.  This will
prevent their TNC from monitoring ANY APRS packets.


GPS UNITS:  I have decyphered the output of the quantity of black box GPS
receivers that were donated to National CAP.  They are Motorola's and can
be switched from the proprietary binary format to NMEA with a simple command.
I wrote the MOTOROLA.BAS program that makes it easy to reset the GPS units
and to send them the NMEA timing requirements.  These devices will make
excellent GPS trackers!


REGISTRATION:  Since most CAP communications personnel are also radio
amateurs and will probably want to use APRS for both HAM and CAP applications,
each additional call sign registration (submitted at the same time) per
individual has been discounted to only $9 each if included in a normal HAM
registration.  CAP only registrations are the same as HAM registration and
asking for additional calls for the same individual at a later date takes
$14.  Quantity pricing of calls in groups of 10 or more is also
available see F1(HELP)-V.

