My ADSB Receiver Box – GPS Precision Time – Upgrade 1

Here is a first upgrade for my ADSB receiver box – GPS precision time. The MLAT position calculation for aircrafts depends on a precise time. While there is already a time synchronization between MLAT receivers in a specific area it is also possible to add a precise time source to improve the calculation result. A GPS receiver is such source when equipped with a PPS (pulse per second) output. The PPS is a signal with a width of less than one second and a sharply rising or abruptly falling edge that accurately repeats once per second with low jitter. The GPS time and PPS signal  are then used to sync the internal ntp time service and keep a low offset and jitter.

Adafruit GPS Breakout v3 connected to Raspberry Pi

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Inside the GPS-GSM Tracker

Got a GPS-GSM tracker today which I ordered some days ago at eBay.
http://www.ebay.com/itm/320762016759

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

[Update]

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.