Infrastructures and Equipment
Basic equipment for all RAEGE Core Site is:
- 1 radio telescope of VGOS specifications (13.2 m antenna diameter; operation with frequencies ³ 45 GHz and up to 90 GHz; fast slewing speed)
- 1 permanent GNSS station
- 1 gravimeter
- Maser clock
- 1 Seismograph/accelerograph
Radioastronomers 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.
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 that can be enhanced up to 100 GHz by using additional options.The telescope is mounted on a concrete tower, which consists of two levels. The ground floor level is for electrical cabinets, and the first level accommodates the azimuth cable twister. The telescope is fully steerable. There is an azimuth axis to rotate the antenna structure along the vertical axis and an elevation axis to rotate the reflector along the horizontal axis. Furthermore, a hexapod positions the subreflector. The antenna is equipped with two computer control systems, one for the main axis (ACU) and one for the hexapod (HCU).
The main figures of the radio telescope are:
Azimuth range: +/- 270°
Elevation range: 0 +100
Main reflector diameter: 13.2 m
Subreflector diameter: 1.55 m
Distance main reflector vertex from elevation axis: 3.270 m
Max. Azimuth slewing speed: 12°/s
Max. Elevation slewing speed: 6°/s
The optical configuration of the radio telescope is Ring Focus, which provides a high efficiency antenna with no reflection back to the feed and no blockage of the subreflector.
For geodetic telescopes, it is essential to measure accurately the position of the intersection of the azimuth and elevation axes. Therefore, a concrete pillar is installed at the centre 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.
Two types of receivers have been developed at Yebes Observatory: The Tri-band receiver and the Broad-band receiver.
-RAEGE Tri-band receivers
The VGOS RAEGE tri-band receiver work at S/X and Ka bands. They have been developed at Yebes laboratories and constructed for the first RF and VLBI tests.
The main advantages of this world class tri-band cryogenic receiver are the simultaneous S/X/Ka operation with dual circular polarization, the backward compatible with legacy VLBI stations, X/Ka VLBI measurements, the reduced feed size for cooling down to 15 Kelvin, and the easy cal signal injection in front of LNA's. It also allows characterization of radio telescope pointing, tracking and gain at high frequencies (32 GHz).
The average receiver noise temperatures are 21 Kelvin in S-band, 23 Kelvin in X-band, and 25 Kelvin in Ka-band. The antenna efficiency that can be achieved with this feed and a ring focus antenna is between 0.65 and 0.75.
Three of these receivers are currently running at Santa Maria (Azores), Ishioka (Japan) and Ny-Älesund (Norway).
More information can be found at: http://www.oan.es/raege/cact/p...