Radioastronomers usually try to detect very weak signals emitted by objects very far from Earth. Instruments used in land -based radio astronomy are large antennas or antenna networks equipped with the most sensitive receivers available, i.e., the noise they produce should be minimal to avoid its overlap to the signals received. Usually radio astronomy receivers are cooled to very low temperatures since some of the electronic devices used to amplify or mix radio signals add less noise if they are cooled.
In the frequency range of 500 MHz to 50 GHz, the components most often used at the entrance of these receptors are amplifiers with high electron mobility transistors (High Electron Mobility Transistors - HEMTs). These devices can be cooled to cryogenic temperatures (~ 15 Kelvin = -258° Celsius) for minimal noise. Once the weak radio astronomy signal is amplified, it is relatively immune to noise added in later processes.
For higher frequencies, the input signal is first converted to a lower frequency by a mixer and subsequently amplified by a cryogenic HEMT. In modern heterodyne receivers for millimeter and submillimeter wavelengths (up to several hundred GHz) the mixer is typically a SIS junction ( Superconductor - Insulator - Superconductor ) cooled to the temperature of liquid helium (4 Kelvin = -269° Celsius ), while at the THz range the so-called hot electron bolometers (Hot electron bolometers - HEB ) used are cooled to even lower temperatures.
The VLBI2010 RAEGE radio telescope
The construction work began on the new VLBI2010-type radio telescopes, part of the Spanish/Portuguese RAEGE project, initiated at the end of 2010 when the contract for the design, construction, and commissioning of the first three radio telescopes was awarded to MT Mechatronics (Germany). The design of the radio telescopes was completed in the summer of 2011. During 2011 and 2012 the backstructures of the three radio telescopes were built by Asturfeito in Cantabria, Spain. Other parts, such as the reflector panels, were fabricated by COSPAL Composites in Italy.
The RAEGE radio telescopes are Azimuth/Elevation turning head telescopes, reaching azimuth and elevation slew speeds of 12°/s and 6°/s, respectively. The optical design is based on a 13.2-m ring focus reflector. In its basic configuration, the observation frequency is in the range of 2–40 GHz. It can be enhanced up to 100 GHz by using additional options. For geodetic telescopes it is essential to be able to accurately measure the position of the intersection of the azimuth and elevation axes. Therefore a concrete pillar is installed at the center of the telescope tower, allowing the installation of a measurement system to be located at the intersection of axes and visible from the outside through openings. Another important requirement in geodetic VLBI is path length stability. In order to handle path length errors, an active deformation measurement and “flexible body compensation” (FBC) method is foreseen, similar to established methods used for surface and focus/pointing error corrections.
The VLBI2010 RAEGE tri-band receiver
The tri-band receiver at S/X and Ka bands, developed at Yebes Labs, constructed for the first RF and VLBI tests. More information in:
RAEGE Broadband receivers
A new broadband receiver of VGOS specifications has been developed for RAEGE. More information on the spiral broadband antenna is available at http://www.oan.es/raege/cact/publicdocs/lopezfernandez-IVSGM2014.pdf.