How is this system different from listening with Yagi antennas?
When you listen to a radio signal with a handheld receiver, you are listening to the amplitude of the signal, that is, how much energy is being received. Your ear compares the amplitude of one transmission beep to the next as you point the antenna in different directions, and hope that the transmitter isn’t being wiggled too much by the animal and the amplitude coming off the transmitter toward you is constant from beep to beep. However, there is another aspect to the radio signal, the phase, or where in the sinusoidal wave the signal is when it hits the antenna. The key to our approach is using the phase difference of the four antennas using synchronized (technically “coherent”) receivers. Instead of comparing one transmission beep to the next, the one transmission is detected at each of the four dipoles on the tower array, and the comparison between them (called “correlation”) provides the information to calculate the angle of arrival.
