Optimization of radio tracking frequencies

The three major factors which limit the performance of animal radio tracking systems: propagation loss, antenna detuning, and signal variability are described. Propagation loss for antenna heights from ground level to 2 m at five frequencies between 70 and 1250 MHz has been measured in mangroves and shows high loss at high frequency. However, an analysis of the environmental sensitivity of small antennas shows that high detuning losses are easily obtained at low frequency; these two factors combine to give a broad optimum frequency range between 500-1000 MHz. Using a simple scattering model it is shown that signal variability, caused by scattering from surrounding vegetation, rises rapidly with frequency. As a result the lowest practical frequency is recommended; in the case of the animal tracking system modeled here, frequencies of 500-800 MHz appear best.