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Session 30 - Radio Astronomy, Yesterday, Today and Tomorrow - I.
Oral session, Tuesday, June 11
The major upgrading of the Arecibo 305-m telescope, expected to be completed early in the second half of 1996, will greatly increase its sensitivity and frequency coverage. These improvements are primarily being obtained by replacing the line feeds currently used to correct the telescope's spherical aberration with a dual reflector Gregorian feed system which will bring an incident plane wave to a true focus. The dual reflector system illuminates a 213 m by 237 m elliptical area on the primary reflector, which is offset to prevent spillover for zenith angles (ZA) < 15^\circ. Beyond this ZA spillover results in a decreasing gain, but a recently installed 16-m high ground screen around the perimeter of the primary reflector shields against ground radiation until a ZA of approximately 18^\circ. Ground radiation will then cause a small increase, approximately 3K, in system temperatures at the telescope's maximum tracking ZA of 20^\circ.
At zenith, the Gregorian feed system will provide a sensitivity of approximately 11 K/Jy in the 1 to 2 GHz band. At lower frequencies, diffraction effects will reduce the sensitivity to approximately 9 K/Jy at 300 MHz. At higher frequencies, the current 2.3 mm r.m.s. of the primary reflector will result in sensitivities of approximately 8 K/Jy at 5 GHz and 5 K/Jy at 8 GHz. Above 15^\circ ZA there will be a drop in sensitivity to about 75% of the 0^\circ value at 20^\circ ZA. Above 1 GHz system temperatures are expected to be in the 20 K to 30 K range.
Program listing for Tuesday