SETTING UP AN APRS STANDALONE TRACKER

 

Most GPS units operate at 4800 Baud. Set TNC to a terminal baud rate of 4800.

You will most likely have to build a cable (at least put connectors on a purchased cable) to connect the GPS to the TNC.

Most TNCs use a DB-25 connector while some use a DB-9. To build a connector for the TNC connect the GPS output to Pin 2 of a DB-25. Connect the ground to Pin 7 The input to the GPS could be connected to Pin 3 of the DB-25, but you will probably not be sending data from the TNC to the GPS (but some GPS units may require an initialization string be sent). If you are using a DB-9 at the TNC, use these pin settings. GPS output to Pin 3, GPS input to Pin 2, ground to Pin 5. See the following table for a comparison of a DB-9 and DB-25 pin assignments.

For the male connector (DTE), the pin assignments are as follows:

 

Pin

Signal

Equivalent pin on DB-25

-----

------

--------------------

shell

ground

1

1

DCD

8

2

RXD

3

3

TXD

2

4

DTR

20

5

signal ground

7

6

DSR

6

7

 

 

4

8

CTS

5

9

RI

22

NOTE: If you are building a connector to attach the GPS directly to a computer, I think you will find that you have to reverse pins 2 and 3 (difference between DCE and DTE protocols).

For a standalone tracker, it will require a TNC that has "GPS-aware" commands built-in. Most TNCs, sold in the last few years are "GPS-aware". For older TNCs, an upgrade is usually available. Without this "GPS-aware" command set, the TNC cannot be used as a standalone tracker. It can be used as a full tracker (computer running APRS), or with APRS at a fixed location not running a GPS.

I will list some of the TNCs that I know about and suggest a set of parameters. Some parameters are not set in concrete and must be varied based on the usage.

The general procedure is to configure the TNC with the parameters, issue a special command that puts the TNC in GPS mode, turn off TNC and detach the computer and attach the GPS. When the TNC is turned on, it will be in GPS mode. Some TNCs have a "back door" that allow a connection to a special ID and then after password verification, will allow any parameter to be modified.

The easiest way to set the icon that will be displayed on the APRS programs is by selecting a SSID to be used in conjunction with Mycall. The following table indicates the icon that is used by various SSIDs:

SSID SYMBOL SSID SYMBOL
       
-0 Dot -8 Ships (power)
-1 Ambulance -9 Cars
-2 Bus -10 Motorcycle
-3 Firetruck -11 Balloons
-4 Bike -12 Jeep
-5 Yacht (sail) -13 RV (recreational vehicle)
-6 Helo -14 Truck
-7 Aircraft -15 Van

 

AEA PK-12

   
AUTOBaud off  
TBAUD 4800  
MYcall (use call and appropriate SSID)
UNproto APRS VIA RELAY,WIDE,WIDE (this is good for marathon and just driving around )*
MYA RELAY (might not be good for marathon)*
GLOCtx 6 (will transmit every 60 secs.)*
GNMEA1 $GPRMC (lat, long, speed, direction or $GPGGA)*
GNMEA2 (don’t use 2nd sentence - not handled correctly)
GPSMode 1 (place in GPS mode press enter power off)
   
  (To reset TNC to terminal mode issue 3 CTRL-Cs
  with computer attached to serial port).
   

 

KANTRONICS KPC-3

 

   
ABaud 4800  
CONOK off  
Cwid e 0  
CD software (other viable option is INTERNAL)*
MYcall (use call and appropriate SSID)
MYAlias relay (maybe not for marathon)
MYRemote (usually call and another SSID(-5/marathon))
RText (basically a password-use a std for marathon)
GPSHEAD1 $GPRMC (Could be $GPGGA) *
LTP1 APRS VIA RELAY,WIDE,WIDE (works)*
BLT 1 E 00:01:00 (1 minute for slow moving (trail) vehicles)
BLT 1 E 00:00:30 (30-50 secs for faster vehicles in marathon)
BLT 1 E 00:03:00 (3 - 10 minutes-just driving around)*
INtface GPS (enter/power off/attach GPS)
   
  (to reset to terminal mode, issue 3 CTRL-Cs)
   

 

PACCOMM TNCs

 

 

Some devices use a hardware jumper to determine terminal baud rate. Others use the BAUD command to set terminal and radio baud rates.

 

CONOK off  
MYcall (use call and appropriate SSID)
MYAlias relay (maybe not for marathon)
REMOTE on  
RMTCALL (same as MYR for Kan.)*
PASSWD (same as RTEXT for Kan.)*
GPSTEXT $GPRMC  
LOCation e 6 (60 secs or 3 for 30 secs)
LPATH APRS V RELAY,WIDE,WIDE  
GPS on (set GPS mode -enter / power off/attach GPS)
   
  (to exit GPS mode enter a backslash )
   

* Indicates parameters that might change depending on circumstances.

 

For the marathon, timing values would be much quicker than in JDA (Just Driving Around).

 

NOTE: After using a Kantronics or Paccomm TNC as a standalone tracker, it is imperative that the transmit timers be reset to zero before using in normal service. Otherwise, the last position stored in the buffers will continue to be transmitted at the specified time intervals.