The invention relates to a piston engine which is essentially comprised of an engine shaft and a set of modules, each of which comprises a cylinder and a piston powered by the engine shaft in the cylinder, each module resulting in vibratory excitation of the engine at a determined fundamental frequency. The first waveguide has one end that is coupled to a RF input port that receives a RF transmission signal and another end that is coupled to a RF bi-directional port that receives a RF reception signal and that transmits the RF transmission signal. The apparatus is characterized in that the shutting means comprise, in turn, a shutter moved according to an arrow by the action of intermittent pressurized air that flows in a control conduit forming part of said shutting means.