G6GVI’s guide to getting
started with your Tracker
Different models
There are two US-based companies currently producing APRS Trackers:
Byonics in Las Vegas make the TinyTrak range;
Argent Data Systems in California make the OpenTrackers.
Their two product lines are very similar, and their interfaces are identical, so once you’ve made
up suitable patch-leads for your radios and GPS, they are interchangeable.
Patch leads
There are only two interfaces to the Tracker:
The Radio port (9-way D-type socket), which connects to the transceiver;
The Data port (9-way D-type plug), which connects to the GPS or PC COM-port.
Radio port
This includes connections for DC power input, PTT, and audio in and out to/from the radio.
The Tracker includes a 5V linear regulator, so an input of a least 7.5V (anywhere between 7.5
and 15V) is required. +Vcc is applied to pin 7, with ground on pin 6.
The audio output from pin 1 on the Tracker needs to be connected to the microphone input
on the radio.
The PTT output from pin 3 on the Tracker needs to be connected to the radio’s PTT line.
Note that most Trackers are supplied with an internal resistor (usually 2.2k) fitted between pins 1
and 3 (R3 in the OT, or R8 in the TT). This is designed to operate the combined PTT/mic input
on most handheld transceivers, but must be disconnected for radios with a separate PTT line.
Since I use my Tracker with both handie and mobile radios, I’ve removed the internal resistor,
but fitted 2K2 inside the D-type plug of the patch-lead I’ve built for use with the handies only.
The audio (loudspeaker) output from the radio needs to connect to pin 5 on the Tracker.
Note that the Tracker can’t actually decode incoming packets, but it uses a simple noise-detector
on the audio to determine whether or not the channel is busy. This is used to prevent the Tracker
from transmitting until the channel is clear, to reduce the chance of interference.
Full wiring diagrams for connections between the Trackers and most radios are published here:
Data port
This handles bi-directional serial data at 4800 baud on an “RS-232” interface. The voltage levels
are bipolar (typically between ±5V and ±9V). See the following Configuration and GPS
Interface sections for more details.
Before it can be used on-air, the Tracker needs to be connected to a PC, to set up its
configuration (once these are set, they are stored in non-volatile memory).
The PC connection is made via the serial “COM” port – a 9-way D-type. Some newer laptop PCs
don’t have these, so a “USB/RS-232” COM-port adapter will be required.
The connection to the PC must be by a “Null-modem” lead or adaptor, which has the following
There are a number of different parameters which need to be set.
In some cases, the terminology is slightly different between the two Trackers:
Digi Path
Auto TX Delay
TX Delay
Auto Transmit
TX Interval
Status Text
Send Altitude
Only send Valid
(Don’t) require
GPS fix
Usually add a -9 SSID suffix after your callsign
(this is a convention for mobile stations)
“RELAY,TRACE2-2” (this governs how your signals will be
digipeated by other stations) 1
select table “/” and “>” for a car or “[” [for pedestrian 2
the time between PTT enable and sending data (if your radio
has a slow-locking synthesizer, or transmit/receive relay, you
may need to increase this to ~ 500ms)
how often do you want your beacons to be transmitted? (Set a
fixed interval, or use SmartBeaconing, where the rate depends
on your speed)
space for your own comment.
(keep this brief, or your packets will become too long)
It’s best to send the text separately after every few (3 or 5)
position beacons.
if your GPS reports altitude, this can be included in your
position beacon (but it increases the length of the packet)
prevents transmission of position packets if the GPS loses lock.
encodes the position in a compressed format, to reduce the
packet length
allows you to change the rate of beacon transmissions
depending on your speed, and when turning corners
Note that both Configuration programs suggest a default path of “WIDE,WIDE”: this setting is used in
the USA, but not in Europe.
A full listing of symbols may be found here: http://wa8lmf.net/miscinfo/APRS_Symbol_Chart.pdf
Once all the parameters are set to your preferences, Write the configuration to the unit, and also
Save it to a file on your hard-disk.
Note that both Trackers support two different configurations (or “profiles”), selected by an
internal jumper. I’ve brought this out to a switch on the case, so that I can quickly select between
the two in the field.
The TinyTrak configuration window looks like this:
The MIC-E “Message” field is akin to the “Position Comment” in the Kenwood D-radios:
The OpenTracker configuration window looks like this:
Since the SmartBeaconing mode has been selected, the “TX Interval” has been greyed-out. (the
SmartBeacon settings are displayed in a separate window, once the “Settings” button is pressed).
GPS interface
The Tracker is designed to read the output from the GPS unit in NMEA 0183 format, at 4800
baud only. The simpler GPS units normally default to this, but the “smarter” ones may need to be
set up in their Interface menu.
If you have a serial lead which connects your GPS to a PC COM port, this will also be suitable to
connect to the Tracker. Otherwise, all that’s required is to connect the GPS “TX Data” output
to pin 2 on the Tracker, and the signal ground to pin 5.
The newer versions of the Trackers (TinyTrak3+ and OpenTracker1x) can also supply a
regulated 5V DC output to power up an external GPS receiver: this is available on pin 4, once an
internal jumper has been fitted. Otherwise, the GPS should be powered off its own independent
In order for the Tracker to work, it must be connected to a GPS receiver producing live data, so
the receiver must have good visibility of the sky. Both Trackers provide an LED indication that
the GPS data is good: the TinyTrak has its own green light, whereas the OpenTracker flashes its
multi-function light once per second.
Setting audio levels
The Tracker’s audio output level is controlled by a pre-set potentiometer on the PCB. This must
be set for the correct modulation (FM deviation) level on the transceiver in use.
To do this, set the Tracker to transmit every 10 seconds, and whilst running the transmitter into a
dummy-load, monitor its output on another receiver. It’s easy enough to set the level “by ear”,
but if you wish to do it visually, try connecting the receiver to a PC sound-card, and use the
“Sine Wave” window in the “Sound Card Tuning Aid” of the AGW Packet Engine program.
The only other adjustment is to set the threshold of the noise detector: make sure that the LED
indicates when the receiver’s squelch is opened, and that it goes out when the channel is quiet.
On-air testing
Once everything is set up, have a look at the Tracker’s output off-air on your home-station APRS
receiver. If you don’t have one, or know any local stations who can check this for you, try taking
your Tracker system up to a local high-spot, and running it for half an hour or so. Then go back
home and have a look at an on-line APRS server, such as:
Enter your callsign-SSID, and see if any of your packets have made it onto the network.
Incidentally, if you find that your indicated position is about 100 yards out, check the “Map
Datum” setting on your GPS: it should be set to “WGS84”, rather than “OSGB” for APRS work.
Burst-after-voice (PTT mode)
This mode is used when voice and APRS are used on a single shared channel. The APRS burst is
triggered by the release of the microphone’s PTT, and sounds a bit like a modulated pip-tone.
In order to use it, the microphone’s PTT must be connected to pin 8 on the Tracker, and different
settings used in the configuration. For more details, see this web-page:
Ross G6GVI
Version 4, July 2007