Inside the GPS-GSM Tracker

Got a GPS-GSM tracker today which I ordered some days ago at eBay.

I plan to use the tracker in my biggest FPV plane for location in case of a long range crash.

The housing is a way bulky and heavy even for a big plane. So could not resist to disassemble the tracker to check if size and weight can be reduced.

Here is the outcome:

Some notes about the hardware:

  • SiRf Star III GPS chipset, stand alone module, soldered to the main PCB
  • GPS antenna is detachable, fixed by two solder blobs
  • plug-on GSM module
  • GSM antenna seems to be crap, but there is a U.FL socket on the GSM module to connect a better antenna
  • 8-pin USB Connector, at least the USB logo is on the charger plug
  • Microcontroller STC 89LE58RD
  • there is a microphone
  • Weight of empty housing: 22.2g
  • Weight of PCB including GSM modem: 21.6g
  • Weight of battery: 18.3g


I have added a picture which show two pads for the microcontrollers serial interface.
Parameters are 19200 Baud 8N1. After power up (without SIM card) there is a loop transmission of AT+CREG.

2.45 GHz Helix Antenna

A last helix to cover all interesting frequencies for FPV.

Antenna dimensions:

  • Design frequency 2450MHz
  • 8 turns
  • Wavelength 0.23
  • Internal diameter 41mm
  • Wire diameter 2.5mm
  • Coil spacing 28mm
  • Reflector diameter 80mm
  • Wave Trap size 15.2mmx7.6mm
  • Feed point height 5mm (wire center), see pictures

5.8 GHz Helix Antenna

This is an example how one can hit the target on spot with a clean build even on 5.8GHz.

Antenna dimensions:

  • Design frequency 5800MHz
  • 8 turns
  • Wavelength 0.23
  • Internal diameter 17-17.5mm
  • Wire diameter 1mm
  • Coil spacing 11.8mm
  • Reflector 40mmx40mm
  • Wave Trap size 6.5mmx3.2mm
  • Wave Trap spacing from feed point 2mm
  • Feed point height 2.5mm (wire center), maintained over 1/4 turn

1240MHz/1280MHz DIY Helix Antenna

Just finished with my helix antenna, designed for 1240MHz.
Used the helix calculator from
Parameters were 1240MHz, 8 turns, 0.23 wavelengths.

My internal helix diameter is roughly 80mm with a coil spacing of 55.5mm. Wire diameter is 3.5mm/10mm².
Reflector size is 250mmx250mm. Center support is made from 6mm Balsa, soaked with epoxy resin.
For matching the IBCrazy wave trap method is used. Trap size is 30mmx15mm. See also


1.2GHz FPV Receiver customized control

In a previous post I described how to control the internal tuner module of a common 1.2GHz FPV receiver by a PC.

Since this setup was only for general tests I put some more efforts and put an AVR tiny44 in control.

On a 4 channel receiver I removed the original micro-controller and replace it by a AVR tiny44, running on internal 8MHz oscillator.
The tiny44 takes inputs from the 4 DIP switches and controls the tuner by I2C and the LED.

Attached to this post is the source code for the tiny44, written for WinAVR compiler.

With this code you have the following functionality:

DIP1 DIP2 DIP3 DIP4 Function
ON OFF OFF OFF Favorite frequency 1, default 1240MHz
OFF ON OFF OFF Favorite frequency 2, default 1280MHz
ON ON OFF OFF Favorite frequency 3, default 1276MHz
OFF OFF ON short OFF Manual tune, 1MHz up
OFF OFF OFF ON short Manual tune, 1MHz down
OFF OFF ON long OFF Auto tune, 1MHz up every 100ms
OFF OFF OFF ON long Auto tune, 1MHz down every 100ms

For DIP3 and DIP4 a long press will be >1 second.

The frequency set using DIP3 and DIP4 will be stored in EEPROM 5 seconds after last tuning action (DIP switch used).
After power cycle this frequency will be the start for new tuning.

Frequency range for manual/auto tuning is 850MHz to 2200MHz in 1MHz steps.

Wiring is given in the source code, header of main.c.

FPV Receiver Control
FPV Receiver Control
Version: 1.0
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