Other
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsa32a..01s&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #SA32A-01
Other
[2403] Ionosphere / Active Experiments, [2494] Ionosphere / Instruments And Techniques
Scientific paper
The design of the new Arecibo HF facility gives efficient illumination of the 305 meter dish without compromising the use of other feeds. When complete, it will provide 83 dbW at 8.175 MHz, and 80 dbW at 5.1 MHz. Illumination of the 305 meter dish uses dipoles near the surface of the dish transmitting upward to a sub-reflector that illuminates the main dish. There are three crossed dipoles for each of the two frequencies. Each dipole section is fed from one of six 100KW transmitters The sub-reflector will consist of a metal mesh with five foot openings, shaped approximately as a catenary rotated about a vertical axis, but actually hexagonal rather than circular at the top. It is held by cables from the three main towers. The dipoles will be supported on towers mounted on concrete pads underneath the dish. The dipole elements can be stowed along the tower sides between operational campaigns. The six towers, three for each frequency, pass through the surface of the dish, requiring the removal of two panels for each. Each dipole element is connected to a transmitter through a three inch coax line. The six transmitters are located in a steel building located several hundred feet from the 305 meter dish. The electrical substation that provides power to the transmitters and the heat exchangers which provide cooling are located outside this building. At this time, the six transmitters in the building are ready for the final wiring. The duct work for the air cooling is complete the the blowers are installed. The pipes for the water cooling are in place and connection to the pump located with the heat exchangers is underway. The trays for the coax lines have been installed from the transmitter building to underneath the dish. One line has been installed in order to verify that this can be done easily. The others will be installed when the civil work underneath the dish is complete. Four one MW generators are on site and being installed. These will provide a flexible and complete power system for planetary radar, the HF facility, and site backup. Design of the mesh is complete and the construction phase has started. One of the tower base concrete pads will sit on ground that is softer than expected and this pad is being designed by the engineering firm Amman and Whitney. The other five use the standard design provided by the tower manufacturer. Amman and Whitney are also reviewing the mesh support design and have recommended some changes in the cable support system in order to provide better temperature stability. As the project construction is completed in the next few months, we face the problems of producing a practical scientific facility. This facility is inherently a lot less complicated than the HAARP facility in Alaska. Nonetheless, a computer control and monitoring system is very desirable, both to allow the most complete control over the transmitted waveforms, and to allow the highest reliability of operation. We are currently reviewing the best ways to accomplish this. We expect that a basic system will be in place for the first couple of operational campaigns, with full flexibility coming later. The basic operation would be similar to our previous facility at Islote, vertical operation with continuous wave or a simple pulse sequence on a single frequency.
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