Very Long Baseline Interferometry – VLBI


Radio Interferometer: In radio astronomy: an instrument combining the amplitudes and phases of the signals received by different antennas. Such an instrument permits to improve significantly the angular resolution in mapping the distribution of the sky brightness as seen from the ground. This implies the ability to investigate extremely fine details of the apparent structure of the radio sources.
The process of combining or correlating the signals from the different interferometer elements requires, besides two or more separate antennas that each receive radiation from the same source, a central computing correlator, in order to reconstruct the map of a radio source from data recorded along many hours. One of the advantages of interferometers is that they are able to reject background noise collected at single antennas (when this noise is uncorrelated over the full array); their a disadvantage is that their field of view is quite limited. This implies that a sky survey over a finite solid angle of the sky, requires a much more observing time than when a single dish instrument is used.

Very Long Baseline Interferometry – VLBI: when the mutual distances of the interferometer elements are several hundred or even several thousand kilometers, special recording techniques are needed at each element or station in order to preserve the phase of the radioastronomical signal, an atomic frequency standard is used as the local oscillator; many TeraBytes of data are recorded per day. These data are later sent to a central correlator centre for the final processing.

European VLBI Network:

Full members of the European VLBI Network, EVN:

  • China: Shanghai Radio Observatory and Urumqi Radio Observatory
  • Germany: Effelsberg Radio Observatory
  • Italy: Medicina Radio Observatory and Noto Radio Observatory
  • the Netherlands: Westerbork Radio Observatory
  • Sweden: Onsala Radio Observatory
  • United Kingdom: Jodrell Bank Radio ObservatoryAssociate members of the European VLBI Network, EVN:
  • Germany: Wettzell Radio Observatory (geodetic VLBI)
  • Finland: Metsähovi Radio Research Station
  • Poland: Torun Radio Observatory
  • Spain: Yebes Radio Observatory
  • Ukraine: Simeiz Radio Observatory
  • South Africa: Hartebeeshoek Radio Observatory

Other arrays:

  • Australia: Australia Telescope
  • United Kingdom: MERLIN
  • U.S.A.: Very Large Array, VLA
  • U.S.A.: VLBA


VLBI can be distinguished as a terrestrial radio astronomical facility and space VLBI.

Frequency bands used by the European VLBI Network

  • The EVN observing frequencies are listed here.

Frequency bands used by the Russian VLBI stations:

  • 0.315 – 0.335 GHz (Pushchino, Medveziy Ozera)
  • 1.385 – 1.435 GHz (Kalyazin)
  • 1.645 – 1.695 GHz (Pushchino, Medveziy Ozera)
  • 2.075 – 2.325 GHz (Kalyazin)
  • 4.805 – 4.855 GHz (Pushchino)
  • 5.000 – 5.020 GHz (Medveziy Ozera)
  • 7.80 – 8.7 GHz (Kalyazin)
  • 22.195 – 22.245 GHz (Pushchino)

Committee on Radio Astronomy Frequencies