English: An experimental parabolic antenna used by radio pioneer Guglielmo Marconi in investigations of directional radio transmission 1917-1922, It consists of a dipole antenna at the focus of a parabolic reflector made of metal rods 1.5 wavelengths long. The reflector directs the radio waves from the dipole into a beam. The source said the wavelengths used in these experiments were 2 and 3 meters (150 and 100 MHz), although at these wavelengths the antenna should be somewhat bigger. With a special spark gap transmitter C. S. Franklin, Marconi's chief scientist, transmitted a distance of 20 miles.