434 MHz GPS Tracker

Project Aim:

To send position reports from a glider back to a fixed base to display on a screen.

Components:

1. 434 MHz easy radio module, 10 mW and 19k2 on air baud rate.

2. GPS 15 OEM GPS running 4800 baud on the serial line

3. PIC 16F628

4. OLIMEX PIC 16 pin development board - PSU and MAX232 on board

Software:

The 16F628 PIC running at 20 MHz, takes the $GPRMC NMEA sentence from the GARMIN GPS15 at 4800 baud, and extracts the latitude, longitude and GPS status.

If the GPS has no lock - the system sends "NO LOCK"

If the GPS has lock, it sends a packet every second.

The PIC is constantly switching between 4800 baud (GPS RX) and 19k2 (Radio TX).

UI-VIew was used to feed the transmitted data into. The tracking run was recorded for later playback.

VK4TEC-12>APRS,WIDE: <<UI>>:=2800.93S/15240.75E'
VK4TEC-12>APRS,WIDE: <<UI>>:=2800.93S/15240.75E'
VK4TEC-12>APRS,WIDE: <<UI>>:=2800.93S/15240.75E'
VK4TEC-12>APRS,WIDE: <<UI>>:=2800.93S/15240.75E'
VK4TEC-12>APRS,WIDE: <<UI>>:=2800.93S/15240.75E'

Radio:

I tried radiometrix devices - but you need to write your own radio protocol. Then I found easy radio. They are basically a 434 MHz TX/RX with the preamble, bit toggling and CRC all built in.

The payload of a easy radio is 180 characters max , and if you wait two characters, the thing will TX.

You need to talk to the easy radio at 19k2 from the PIC. The on air baud rate is also 19k2.

At the receive end, you need a matching easy radio RX. this is also 19k2. Thru a MAX232 chip - into the computer.

There are no tones - just FSK. I measured the databurst at around 20 ms. Spectrum is about 100 kHz.

Hear what it sounds like

Antenna:

On the car was a dual band ham radio antenna, solder onto the pins of the receiver.

In the air, was a telescopic antenna , again soldered to the leads of the transmitter.

I checked it with a spec analyzer, and it was +10dbm on 434.000 Mhz, with 100 kHz BW.

Indicators:

On the front of my box I have two LED's - A blue one and a Red one. The blue one flashes when the GPS is locking, and is constant when it is locked. The red LED shows the key up of the transmitter.

Test run:

I set the system up and went for a drive, with mobile flutter etc - I got around 1.9 km's which was not too bad.

Test two was to fly the box in a glider - where i saw favorable results out to 3/4 kms and two single bursts at 7/8 kms when the pilot held it up straight and high in the cockpit.