Ham Radio 2000/Ham Radio 2000.iso/ham2000/packet/aprs75c/aircraft.txt

Text File | 1996-04-10 | 9KB | 179 lines

AIRCRAFT.txt 7.5b         NOTES ABOT AIRCRAFT, ACARS
                              CIVIL AIR PATROL
                                  and the
                  APRS INTERFACE TO ARNAV SERIAL DATA FORMAT
                       FOR AERONAUTICAL LORAN/GPS UNITS

NEW:  There is now a special APRSair.exe which can parse and display
ACARS data and posits.  ACARS is the internaltional Airline Packet Data
system operated on 131.55 MHz.  See ACARS.txt.

3D ALTITUDE DISPLAY:  The Y-AXIS command displays a 3D perspective with
the horizon infinity at the screen center.  The 2D map center appears
near the bottom 1/3rd of the screen in 3D and Altitude is displayed along
the right screen edge.  Altitude is obtained from the string "/A=XXXXXX"
appearing in any POSIT.  ALtitude is automatically extracted from the
standard NMEA GGA sentence or from the special $PGRMZ and $PMGLB
sentences, and or it can be manually entered.  Note that the field MUST
be exactly 6 characters with leading zeros.  The ALTITUDE scale along the
right side of the 3D screen is calibrated to the original 2D center of
the map.  THis means that the scale will always be correct, but the true
3D visual perspective my be awkward or confusing for stations that are
near or far to the south or north of the 2D map centerline.

REPLAY the BALLOON and AIRCRAFT.hst files to see the effects.  Notice
that as the aircraft flies to the south (toward you), it will always
stay at the 5000 foot altitude regardless of perspective.  At some ZOOM
ranges, as it departs the airport or returns, it will actually appear
in perspective to have a negative altitude because the SYMBOL is always
going to be displayed at the CORRECT altitude according to the scale
rather than in perspective.


HOW TO MAKE AN AIRCRAFT SYMBOL:  Remember that if you are going to be using
a TNC only transmitter in the aircraft, you must indicate the aircraft
symbol character in either of two ways:

       1) Set the TNC SSID to -7.  i.e.  W3ADO-7
   OR  2) Make the first three characters of the BText be:  {'}.....

In the case of #2, the aircraft symbol will not begin to display as an
aircraft in APRS until the receiving station receives a BText first.  Until
then, the object will appear as a dot.

NEWS:   Jerry Wyatt of the AZ CAP has build a prototype controller
that parses ARNAV data into an NMEA RMC format.  His microcontroller then
sends this string to the TNC once every N seconds.  This is a handy way of
interfacing ARNAV data until the TNC manufacturers do it themselves.


ARNAV FORMAT: Aeronautical manufacturers thumb their noses at the NMEA
specification (for boats) and have no formal standard for GPS.  Several
of them use a format called ARNAV, which is the same as the KING format.
APRS parses ARNAV in two ways.  First, it plots any received packet
that contains the RAW ARNAV data in a packet beginning with the STX
character.  It can also parse RAW ARNAV data comming in the same port
as the TNC without the packet header.  For this to work, the station
must be in SPM or HSP modes and be validated for GPS.  And the GPS and
TNC must be set to the SAME baudrate (4800 usually).  One user says he
has to operate both at 2400 baud to make it work reliably.

   The ARNAV data begins with an STX, has lots of data lines, and then ends
with an ETX.  Each line of data has a single leading character that indicates
what the remaining data on the line represents.  APRS will parse out the
following fields:

AN dd mmhh   (North Latitude in degrees and minutes to the hundredths
BW ddd mmhh  (West Longitude in degrees and minutes to the hundredths
Cccc         (Course)
Dsss         (Speed)
.....        (other fields for E,G,I,J,K,L,M,Q,d,e, and v are given
Wxxxxx N dd mmhh W ddd mmhh +aaaa    (Waypoint where: xxxxx is its name      )
                                                      LAT LONG as shown
                                                      aaaa  is altitude in ft)


Notice, that APRS will not only place the aircraft on the map, but it will
also generate a symbol for the WAYPOINT and place it in the APRS system as
well.  The WAYPOINT symbol is a circle.  The ARNAV station will be a
standard airplane.  Contact me for info on how to change the default SSID
symbol definitions if necessary.

IMPLEMENTATION: Since the data begins with an STX but has numerous carriage
returns in the middle, there is no way to make any of the HAM TNC GPS modes
work on this data.  PacComm has a comercial TNC that will.  Instead, you
have to set the TNC into the UI MODE (unconnected CONVERSE) and just let
it transmit all of the data as it streams in the serial port.  Therefore:

   FOR NOW, THIS WILL ONLY WORK WITH OLDER ARNAV PRODUCTS WHICH HAVE A USER
   DEFINED PERIODICITY.  NEWER 5000 series products output at a 1 second
   rate which (just like the NMEA standard) is too fast for a 1200 baud
   shared packet channel.

   NOTE:  PACCOMM tells me that an ARNAV parser is built into their commercial
   TNC, ready to go, off-the-shelf!  The CAP guys tell me that this is true,
   but newer ARNAV devices output almost a 400 character NAV message.  So
   although the data will be transmitted, it is very innefficient for a shared
   channel to transmit 400 characters worth of data, when you only need 20.

   ALTERNATELY, wire up a 555 circuit that only passes the ARNAV data to the
   TNC for two seconds out of every N period.

Here is how to set it up:

   1.  Set up the aircraft TNC to be permanently in the UNPROTO-CONVERSE
       mode.  In the Paccomm, set UI MODE ON.  Or buy the DRSI APRS rom.

   2.  Set COMMAND $1B.  This changes the COMMAND mode character from its
       normal control-C to be the ESCAPE character.  Actually, you can set
       the COMMAND character to any other character, just NOT ^C.

   3.  Set the SENDPAC character to $03 (^C) instead of $0D (Carriage Return)
       so that the packet is not transmitted until the ARNAV ETX character
       ($03) comes along.

   4.  Set your ARNAV device to output data once every 30 to 60 seconds
       or so, depending on channel activity.

   5.  If you cannot change the ARNAV periodicity, set up a 555 chip to only
       send the data to the TNC for 2 seconds out of every N period.  In this
       case, you must also set CPACTIME ON, so that the TNC will go ahead and
       send its transmit buffer even if it does NOT get the normal ETX char.
       With CPACTIME ON, the TNC will wait for 1 second after the last
       incomming character and then go ahead and send the data, even if the
       555 oscillator cut off the incomming data.


I DONT HAVE ACCESS TO ANY ARNAV DEVICES.  TRY IT AN SEE!  GIVE ME FEEDBACK
AND WE WILL MAKE IT WORK!



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.  The four quadrants of these grids correlates exactly with
the readily available USGS 7.5 minute maps.  These grid squares have a
standard numbering system within each sectional chart.  Where ever there
is an overlap, the western most map takes precedence.  APRS accomplishes
this ordering by the sequence of maps in CAPGRID.DAT.  Also, ALBUGUERQUE
must be first.  Except for the overlaps, most charts are listed
alphabetically.

The numbers displayed by APRS is determined by the 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.
If you are unsure, zoom out to see where the overlaps are, or move your
cursor to the WEST of the area of interest to force the correct sequence.

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


TRACK HISTORIES:  Back at the SAR headquarters, track histories can be
processed offline by periodically doing a FILES-SAVE to save the latest
track history to file and to a floppy.   This disk can then be taken to
another computer for analysis.   APRS will automatically do a save whenever
199 positions have been received.  After each save, memory is cleared
except for the last position of all stations.


GPS UNITS:  I decyphered the format 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.


REGISTRATION:  Since most CAP comms personnel are also HAMs, secondary
CAP registrations are discounted to only $14 each if included with a
HAM registration.  CAP-only registrations are the same as HAM registration.
Quantity pricing of calls in groups of 10 or more is also
available see F1(HELP)-V.