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Welcome to the AntTracker

 Eric Stockenstrom - First code June 2017

See RC Groups - Build a Tracker

This application reads serial telemetry sent from a flight controller or GPS. The module calculates where an airbourne craft is relative to the home position. From this it calculates the azimuth and elevation of the craft, and then positions 180 degree azimuth and elevation PWM controlled servos to point a small high-gain antenna (like a 5.8GHz double bi-quad) for telemetry, control or video.

The code is written from scratch, but I've taken ideas from Jalves' OpenDIY-AT and others. Information and ideas on other protocols was obtained from GhettoProxy by Guillaume S.

The target board is an STM32F103 "Blue Pill", chosen for its relative power, small size and second (multi) serial port(s) for debugging.

To use the module, position the AntTRacker with the antenna facing the direction of your planned take off. Position the craft a few metres further, also facing the same heading for take-off. The flight computer will determine the magnetic heading, from which all subsequent angles are calculated.

NOTE: In Mavlink Passthrough mode only, relative altitude is GPS (not barometer) derived, so altitude is inaccurate until at least 10 satelites are visible.

Instructions: 1 Power up the craft. 2 Power up the telemetry source, like Taranis, 3DR modem or ground Raspberry board. 3 Power up the AntTracker. 4 When AntTracker successfully connects to the telemetry source, the LED on the front flashes slowly. 5 When AntTracker receives its first good GPS location frame, the LED flashes fast. For Frsky Mavlink passthrough only, more than 10 visible GPS satellites are required, and HDOP must be 3 or greater. 6 Push the home button to register the home position and heading. The LED goes on solid. 7 Enjoy your flight! The Tracker will track your craft anywhere in the hemisphere around you (but not closer than MinDisplacement = 4 metres).

The small double bi-quad antenna has excellent gain, and works well with a vertically polarised antenna on the craft. Other receiver blocks can be added for diversity, and some improvement in link resilience has been observed despite the possibly lower gain of the other links. Of course it would be possible to stack double bi-quad antennas on the AntTracker, but more robust mechanicals will be called for.