Building an APRS Tracker

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Build a turnkey APRS tracker for about $350

These instructions are detailed and complete. Enjoy !! - Rich W7KI

For reference, pictures are at the bottom of this page.

1. Buy the equipment

Item Make/model $$$ Source

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

GPS Garmin GPS35-HVS 148 (Star Lite Intl)

                                  or (GPS City)

TNC Byonics Tiny-Trak II 35 (Byonics) Radio Yaesu FT-1500M 145 (Austin Amateur Radio Supply)

                                  or (R&L Electronics)

Cable Yaesu CT-39A 14 (Radio Depot)

                                  or (R&L Electronics)

Box (3x2x1") 270-1801 2 Radio Shack Plug (9-pin male) 276-1537 2 Radio Shack Plug (9-pin female) 2 Radio Shack Cable 270-026 3 Radio Shack (you will need two of these) Hood 276-1513 2 Radio Shack Cap .01uf capacitor Choke Ferrite bead/clip-on

2. Build the Tiny-Trak II. Do not install resistor R9.

  On the bottom of the PC board add a .01uf capacitor between the base and
  emitter of Q1. This will decouple RF to ground preventing a potential
  transmitter lockup condition.

3. Download the Tiny-Trak config progam, power up the Tiny-Trak unit

  (if 12 volts isn't handy by your PC a 9-volt battery will do) and
  connect the Tiny-Trak II to the serial port of your PC.
 Configure as follows:

  Callsign: WD7ABC-2  (your callsign & SSID, typically -2 or -3 for a mobile)
  Digi Path: WIDE1-1,WIDE2-1 (for mobile station)
             WIDE3-3 (for a base station)
             Digi Path settings vary in different areas.
  Symbol: >
  Table Overlay: /
  KeyUp Delay: 180ms
  Transmit Every: 90 seconds (its not important, SmartBeaconing overrides this)
  Quiet Time: 1500 ms
  Calibration: 128 (adjust for your specific TinyTrak II)
  Status Beacon Text: monitoring 146.52 (or whatever freq you monitor)
  Send Every: 1 transmissions
  Transmit Altitude: Y
  Only Send Valid Position: Y
  MIC-E Enable: N
   (other MIC-E settings not important)
  Time Slotting: Disabled
  SmartBeaconing: Enabled
     " Min Turn Angle: 30 degrees     (these figures work good for corner-pegging)
           Turn Slope: 50 mph-degrees
       Min Turn Time: 5 seconds
         Slow Speed: 3 mph
         Slow Rate: 60 seconds
         Fast Speed: 45 mph
         Fast Rate: 120 seconds

4. Configure the radio

   Connect 12 volts & power it up
   Spin the dial to 144.39
   Set power level to "Low3" (25 watts)
   Hold down MHZ key to get into "set" mode
   Spin dial to "PCKT", press MHZ key, spin dial to "PKT ON", press MHZ key
   Spin dial to "TOT", press MHZ key, spin dial to "1M", press MHZ key
   Spin dial to "BEEP", press MHZ key, spin dial to "OFF", press MHZ key
   Spin dial to "PRATE", press MHZ key, spin dial to "1200", press MHZ key
   Spin dial to "DIMR", press MHZ key, spin dial to "OFF", press MHZ key
   Spin dial to "LOCK", press MHZ key, spin dial to "K+D", press MHZ key
   Hold down MHZ key to get back to normal mode
   Turn the volume knob all the way down
   Disconnect 12 volts, do not use the power switch to turn it off
   I recommend 25 watts because I had problems with RF getting into the
   TinyTrak. Some people have been able to use 50 watts without any problems.

5. Connect cable to Tiny-Trak PC board

  Note: The data jack on the Yaesu FT1500M is a 6-pin mini-din, which is the 
        same kind of connector used for a computer keyboard or mouse (PS-2 style,
        not the older 5-pin DIN or 9-pin serial type). You may be able to
        cannibalize a cable from computer equipment provided it has wires going
        to the pins that you will be using.

The CT-39A instruction sheet has an error. There is no white wire. Its actually orange.

The CT-39A cable has 7 wires. The shiny black wire goes to pin 1 and the dull black wire is the shield.

FT1500 TinyTrak PC board

TXD      1 -----Black (shiny)----- AUD+  (2nd hole over from top left)
Ground   2 -----Brown------------- AUD-  (1st hole over from top left)
PTT      3 -----Red--------------- PTT OUT (3rd hole over from top left)
RXD-9600 4 -----Orange------------ (no connection)
RXD-1200 5 -----Yellow------------ (no connection)
Squelch  6 -----Green------------- (no connection)
                Black (Dull)------ PTT- (4th hole over from top left)

6. Hook up the squelch

The squelch output (pin 6) provides 5 volts when a signal is present and 0 volts when there is no signal. This is incompatible with the TinyTrak-II because it operates opposite (5 volts for no signal, 0 volts with a signal). To make this work you could invert the signal with a transistor, or you could run an additional cord and use the speaker output on the radio.

The main difference between these two options is the radio speaker method is an audio-based squelch where the inverted signal method controls the squelch depending on whether or not a signal registers on the S-Meter.

To use the radio speaker (easy way): Get a 1/8" "mini" plug and hook a pair of wires to it. Connect the wire from the plug tip to the 4th hole over from the IC on the bottom right. Connect the wire from the plug ring to the 5th hole over from the IC on the bottom right.

To invert the signal (hard way, but keeps everything in the 6-pin cable): Get a 2N2222 transistor, a 4.7K resistor (Yel-Vio-Red), and a 470-ohm resistor (Yel-Vio-Brn). Remove R9 and C2. Put one leg of the 470-ohm resistor into the top hole of where R9 was. Put the other leg of the 470-ohm resistor into the top hole of where C2 was. (mount the 470 ohm resistor flat on the PC board) Put one leg of the 4.7k resistor into the bottom hole of where C2 was. (mount the 4.7k resistor upright and leave the other leg hanging up in the air for now) Put the emitter of the 2N2222 into the bottom hole of where R9 was. Put the collector of the 2N2222 into the middle hole of where R9 was Bend the base lead of the 2N2222 up to your right and connect it to the

top the 4.7k resistor. Snip off any excess wire.

Connect the green wire from the 6-pin cable into the 4th hole over from the IC on the bottom right.

Once nice thing about the FT1500 is that very weak signals will always register a notch or two on the s-meter, so this inverter circuit should function well. I've had other brands/models of radios where weak signals wouldn't register on the meter.

7. Mount it in a box

To mount the Tiny Trak II into the little 3x2x1 box, you will need to trim the two bottom corners of the PC board. Just make a diagonal cut across the center of the hole. Whatever you do, be careful doing this, as you don't want to damage the board. Don't try to cut it off as one big chunk as this will likely stress the board, use a small pair of wire cutters and nibble through it with a number of small cuts.

Unsolder the 9-pin connector from the Tiny-Trak II, get three 2-inch pieces of wire, and extend the connector away from the PC board. You'll notice Byon left you three holes on the PC board to do this.

Notch the side of the box for the 6-wire cable Notch the side of the box for the power cable. Notch the front of the box for the DB9 connector. If you decided to use the speaker-squelch, drill a hole, notch the box, or add a connector for it.

When notching/drilling the box, make sure the cable entry points don't obstruct the pots or LED's on the PC board.

If you got the Radio Shack power cable, cut it into two sections of equal length (it comes out of the package with a connector on each end), take the connector that has the positive tip exposed and solder it to the power connections on the Tiny-Trak II. The + & - holes are on the bottom right of the TinyTrak.

Mount the 9-pin connector from the outside of the box. Make sure your notch (and the other notches for that matter) is deep enough to clear the lip on the lid of the box. Using the installed connector as a template, poke a couple of holes in the box with your soldering iron (yeah, I know, bad practice) and then secure the connector with a couple of short screws.

Once everything is in place, add a small wire-tie to the power cable on the inside of the box so it will act as a strain-relief.

8. Connect the GPS

The GPS35-HVS has 9 wires. We only need to connect 3 to a male DB-9 connector. Cut off the unused wires. The GPS is set up at the factory for 4800 baud and does not require any configuration.

Wire Usage Connect to

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

Red +12 12-volt power connector (red) Black GND DB9 pin 5, 12-volt power connector (black) White TXD1 DB9 pin 3 Blue RXD1 no connection Purple TXD2 " Green RXD2 " Gray PPS " Yellow PWRDWN " Shield "

note: the red wire might be orange on some units

9. A few final things to do

  Set TX Audio pot (middle left of PCB) to halfway point. If this doesn't
  do the trick then turn it fully counterclockwise.
  If you used the speaker connection for the squelch:
   Set RX Audio pot 1/8 turn clockwise from the halfway point
   Set volume knob on FT1500 to 1/4 (so the little notch on the volume
    dial is pointing straight to the left)

10. Hook it all up and watch it work. At least it worked for me. That is until

   I installed it in the car and it wasn't tracking. I listened to it with a
   handheld receiver and noticed a loud hum on the signal. Turned out to be
   RF getting into the TinyTrak's power cable. This was easily fixed by putting
   a clip-on ferrite onto the positive wire. These ferrites are easy to come by,
   I robbed mine from a computer monitor cable.
   Later on the transmit audio hum came back intermittently. Adding two more
   ferrites to the power cable took care of the problem.
   One other thing I discovered is that the TinyTrak will suffer from RF saturation
   and not function correctly if its too close to the radio. This problem was taken
   care of by keeping a minimum separation distance of 6 inches between them.
   If you experience strange problems the first thing I recommend is setting the
   radio to the lowest RF output level and see if that takes care of it.
   You might need to make miscellaneous adjustments as detailed in the TinyTrak manual,
   mine worked ok with the settings in this document.
   Mike KU4ZD used the same equipment combo in his setup and he had to change R5 from
   220K to 100K because of low transmit audio levels.
   If you need to do further work with the unit, I recommend making a DB9 extension
   cable for your PC (its kind of hard to hang the box off the back of your computer).
   Also, you can use a 9-volt battery for programming/testing. 
   Since you have separate power leads for the GPS and radio you can run the GPS
   on constant 12 volts and run the radio on switched 12 volts. This will slightly
   increase performace because the GPS won't have to reacquire its position every
   time the car is started.

Why I used this equipment:

GPS35 chosen because its a turnkey unit. Give it power and it spits out NMEA lat/lon strings. Since it doesn't have a display it can be mounted anywhere, for example in the rear window or externally on a trunk-mount. The specific GPS35-HVS model is set up for an unregulated 6 to 40 VDC power source which makes it ideal for automotive use.

Tiny-Trak II chosen because of its small size, economical price, and proven reliability/compatibility.

FT-1500M chosen because of its small size, known compatibility with Tiny-Trak, great price (same price as the MFJ dataradio, but with the Yaesu you get a complete synthesized voice/data radio plus 50 watts!), and the Yaesu's capability of working on 12 volts. (The TX on both of my Kenwood 2-meter rigs cuts out on high-power at 12-volts when the engine is off but works fine at 13.5 volts. Since I want the tracker to work with the engine off I need a radio I can count on). I tested the FT1500M down to 11.3 volts on high power. The radio will cut out if the voltage drops into the 10 volt neighborhood during transmit.

Also, the FT-1500M has a data jack on the back so you don't need to

fiddle around with interfacing the mike jack to the TNC.

While the FT-1500M has one of those "soft" power on/off buttons, it does remember the on/off state after it loses power, so you can wire it into the vehicle "ignition-on" and expect the radio to power itself up when +12 is applied to its power leads.

Thanks to the following people for their advice & information:

Byon N6BG Curt WE7U Paul KE7XT Brad N7JGX Mike KU4ZD

Squelch mod: tt2mod.jpg

Programming setup: ttprog.jpg

Ferrite choke on power lead: ttchoke.jpg

Complete system: ttsetup.jpg

GPS-35 fits nicely under brake light: ttgps.jpg

Radio under the drivers seat: ttradio.jpg

TinyTrak stuffed under passenger seat with a mess of other things: ttmess.jpg

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