The Suspended Platform

Suspended 450 feet above the reflector is the 900 ton platform. Similar in design to a bridge, it hangs in midair on eighteen cables, which are strung from three reinforced concrete towers. Another system of three pairs of cables runs from each corner of the platform to large concrete blocks under the reflector. They are attached to giant jacks which allow adjustment of the height of each corner with millimeter precision. Just below the triangular frame of the upper platform is a circular track on which the azimuth arm turns. The azimuth arm is a bow shaped structure 328 feet long. The curved part of the arm is another track, on which a carriage house on one side and the gregorian dome (installed in 1996) on the other side can be positioned anywhere up to twenty degrees from the vertical. Hanging below the carriage house are various linear antennas each tuned to a narrow band of frequencies. The antennas point downward and are designed specially for the Arecibo spherical reflector. A total of 26 electric motors control the platform. These motors drive the azimuth and the gregorian dome and carriage house to any position with millimeter precision.