These antennas collect cosmic radio waves. The grid on the ground serves as a reflector and as a shield for anything coming from inside the earth. The actual antennas are the four wires (i.e. two dipoles) leading up to the tip of the central pole. The knob at the top collects the signals and sends them to a nearby signal processing container.
The most important piece is the wooden log. It wouldn’t work without it. Just kidding, but it is still astonishing that it only takes such cheap antenna contructions to build the world’s highest resolution radio telescope. The main genius is put into the signal evaluation software.