The second Arecibo upgrade

For more than 30 years, the 305 meter diameter radio telescope at the Arecibo Observatory has been a unique tool. Scientists have used it to study the Earth's atmosphere, asteroids and even distant galaxies. The Arecibo facility is a part of the National Astronomy and Ionosphere Center (NAIC). The telescope has been an extremely productive research instrument. However, users have been hampered by needing line feeds to properly illuminate its spherical aperture. While effective at low frequencies, a line feed offers only a narrow bandwidth at an essentially fixed frequency. Observations, thus, have been restricted to very narrow frequency bands at a few specific frequencies between approximately 100 and 2400 MHz. A combination of factors now permits a major enhancement of the Observatory's capabilities. The new ingredients include: much-improved capability for numerical analysis and optimization of reflector antenna systems; advances in structural engineering, and computer control of complex systems. With these new capabilities, an all-reflective corrector system has been developed for the Arecibo telescope. This will significantly enhanced sensitivity over the frequency range from 300 MHz to at least 10 GHz. The details and results of this upgrade are discussed.