Base of antenna mast of AM radio station KTBS (now KEEL) in Shreveport, Louisiana, USA, showing a counterpoise ground screen. The ground screen is a network of horizontal radial copper wires extending out from the base of the mast, suspended on posts above the white helix house, attached to the antenna's ground system. Its purpose is to prevent excessive ground currents, reducing transmitter power dissipated in ground resistance. A counterpoise is similar to a ground screen but extends out further, up to a quarter-wavelength, replacing the ground wires entirely. Alterations to image: lightened dark areas to bring out ground screen more clearly against sky.