A system comprising a first communication device and a second communication device adapted to determine a property of communications between the first and second communication devices. The improved acoustic lens may have a uniform loss along an elevation axis or may have a loss along the elevation axis that provides for an apodization of an acoustic signal. The terminal updates the menu content of the menus based on the menu status of each menu. A sub cooling system including a sub cooling passage for cooling the first exhaust passage is provided.