The Very Small Array (VSA) was a radio interferometer at Teide Observatory in the Canary Islands designed to investigate the cosmic microwave background. It had 14 horn reflector antennas tunable between 26 and 36 GHz, mounted on a tip-able platform (perhaps 10 meters across) and two 3.5 meter 30 GHz dishes. It went into operation in 2000, remaining in use until 2008.
Its 26-36 GHz band does not include the quoted CMB frequency, which is the peak of the CMB black-body spectrum (by some determination), but covers part of the longer-wavelength tail of the spectrum, where its intensity is some fraction of that at the peak. However the observed band has the advantage that it has some visibility from the ground (in the optical window), particularly given the altitude of the VSA's Canary Islands site.