Effelsberg

The 100-m radio telescope of the Max-Planck-Institut für Radioastronomie (MPIfR) is situated in a protected valley near Bad Münstereifel-Effelsberg. It is one of the two largest fully steerable single-dish radio telescopes in the world and is a unique high frequency radio telescope in Europe.

The telescope can be used to observe radio emission from celestial objects in a wavelength range from 73 cm (corresponding to a frequency of 408 MHz) down to 3.5 mm (86 GHz). Observations at short cm- and mm-wavelengths have become increasingly important for all kinds of observing programmes during the last years. The combination of the high surface accuracy of the reflector (the mean deviation from the ideal parabolic form is ≤ 0.5 mm rms) and the construction principle of "homologous distortion" (i.e., the reflector in any tilted position has a parabolic shape with a well-defined, but shifted, focal point) enables very sensitive observations at unprecedented high frequencies for such a large telescope.

With the advent of the new subreflector in 2006, observations from the secondary (Gregorian) focus gained significantly in efficiency (more than 50 % at the high frequencies) due to the very high accuracy of the new mirror (~0.06 mm) and its active surface which is able to compensate small-scale deviations of the main dish due to imperfect homology. The new system is equipped with a hexapod focus driving system, allowing a fast and accurate positioning (better than 0.1 mm) of the receiver in the focal point. A new mechanism allows automatic receiver exchanges between the nine systems located in the secondary focus and the receiver box located in the prime focus. Thus, the telescope has strongly improved its frequency agility. Additionally, new prime focus receiver boxes were developed which contain up to four receiving systems (in contrast with the former situation where only one receiver per box was possible). The first multi-frequency receiver box (with the 18/21, 1.9, and 1.0 cm systems) was tested in summer 2007 and will be fully functional in spring 2008. The construction of more multi-receiver boxes is foreseen for 2008 and 2009.