  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.
= $42^{\circ}~26'$ N, long.= $13^{\circ}~33'$, elevation = 2000 m a.s.l.) in
Central Italy, close to the Gran Sasso Laboratory.
