Arecibo Observatory, Arecibo PR, USA
The previous Arecibo HF facility was located near the north coast of Puerto Rico on low-lying flat land. It was seriously damaged by Hurricane Georges in 1998. At the time, the implementation of Government policy to return the entire surrounding area to its original state as the largest wetland in the Caribbean was in its initial stages, and so it was not possible to consider rebuilding at that site. Lack of other available sites in heavily populated Puerto Rico and the need to design a very cost effective facility drove the decision to use the Arecibo 305 m as the HF reflecting antenna for the new facility. We are now in the process of obtaining the final funding for this project and are in the initial stages of implementation.
The design uses a unique Cassegrain screen, supported from the three main towers, as a secondary. It is driven from an array of three crossed dipoles located just above the the 305 m dish near its center. The computer antenna modeling for the design was performed at the Pennsylvania State University. The screen reflects HF, but is nearly transparent to the higher frequencies used for the incoherent scatter radar and radio astronomy. Six 100 KW transmitters (obtained as Federal excess property from a decommissioned over the horizion radar) feed the six elements of the dipoles. The coax lines that connect the transmitters to the dipole elements were also obtained through Federal excess property. In order to keep the cost of building and operating the facility low and to avoid impact on other observatory operations low, we have avoided designs that require supporting a heavy, high-power feed over the dish as some previous designs have. The parts of the facility that need to handle high power are on the ground or mounted on solid low towers, simplifying construction and maintenance.