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1 Introduction

The study of large samples of radio sources over a frequency range as wide as possible is still an important branch of modern astrophysics because of its cosmological relevance. While early radio surveys naturally discovered strong sources (many of which are also intrinsically luminous), the need for surveys of intermediate or low flux densities became apparent. One important radio survey aiming at lower source flux densities was the so-called B3 survey (Ficarra et al. 1985), carried out at 408 MHz and complete down to 100 mJy at that frequency and naturally delivering a huge number of radio sources, in this case 13354. A subsample of 1050 sources was later observed with the VLA (hereafter B3-VLA sample; Vigotti et al. 1989), the selection criterion ensuring roughly equal numbers of sources in 5 flux density intervals. Measurements of 429 sources at 1.4 GHz and of 770 sources at 4.75 GHz were conducted by Kulkarni et al. (1990). Based on these surveys the spectral properties and their possible spectral evolution has been investigated and discussed (e.g. Kulkarni & Mantovani 1985; Kapahi & Kulkarni 1986).

Our aim is the construction of a homogeneous spectral database for a large radio sources sample 10 times fainter than that of Kühr et al. (1981). The 6C survey (Hales et al. 1988) contributes the 151-MHz flux density, the WENSS (Rengelink et al. 1997) the 327-MHz flux density. The 408-MHz flux density is taken from the B3 survey (Ficarra et al. 1985) while the NVSS (Condon et al. 1998) yields the 1400-MHz flux density. The GB6 survey (Gregory et al. 1996) combined with the work of Kulkarni et al. (1990) provides the 4.75 GHz flux densities for 80% of the B3-VLA sample.

We have therefore embarked on a project to survey the entire sample at 10.6 GHz (i.e. $\lambda$2.8 cm) using the Effelsberg 100-m telescope. Since all measurements were carried out using IF polarimeters we have information about the linear polarization of a large number of sources, which will be reported at a later stage.

In Sect. 2 we describe the observing techniques and data reduction. Section 3 presents the results.


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