At frequencies close to 1 GHz the sky diffuse radiation is a superposition of radiation of Galactic origin , the 3 K Relic or Cosmic Microwave Background Radiation , and the signal produced by unresolved extragalactic sources .
Because of their different origin and space distribution the relative importance of the three components varies with frequency and depends on the direction of observation .
With the aim of disentangling the components we built TRIS , a system of three radiometers , and studied the temperature of the sky at \nu = 0.6 , \nu = 0.82 and \nu = 2.5 GHz using geometrically scaled antennas with identical beams ( HPBW = 18 ^ { \circ } \times 23 ^ { \circ } ) .
Observations included drift scans along a circle at constant declination \delta = +42 ^ { \circ } which provided the dependence of the sky signal on the Right Ascension , and absolute measurement of the sky temperature at selected points along the same scan circle .
TRIS was installed at Campo Imperatore ( lat .
= 42 ^ { \circ } ~ { } 26 ^ { \prime } N , long.= 13 ^ { \circ } ~ { } 33 ^ { \prime } , elevation = 2000 m a.s.l . )
in Central Italy , close to the Gran Sasso Laboratory .