Team member Tim Pegg, KF6LHX, designed a 40 MHz ISM band locating beacon to assist in finding the balloon using a directional antenna after it lands. It is designed to trigger when the balloon falls below around 14,000 feet using a pressure sensor and sends two square wave tones at 700 and 1000 Hz at 40.68 MHz AM modulation. Power output is estimated to be between 10-20 mW, enough, hopefully for a range of 500-600 feet on the ground for final localization.
Etched circuit board
Directional Antenna (small magnetic loop)