1 Introduction

Homogeneous databases over a wide frequency range for a large sample of radio sources with intermediate or low flux densities are an important ingredient to modern astrophysics. We have therefore embarked on a project to obtain flux densities for the B3-VLA sample (Vigotti et al. 1989) over a frequency range as wide as possible. The aim is to study the spectral properties of a complete sample of radio sources.

The B3-VLA sample is composed of sources that are roughly equally distributed in five flux density intervals, i.e. 50 times fainter than the 3C survey (Bennett 1962). The sample now contains 1049 radio sources, instead of 1050 listed in the previous papers dealing with the B3-VLA sample: the source 2302+396 which was already indicated as a possible spurious source close to a grating ring in the B3 catalogue (Ficarra et al. 1985) was deleted from the list since it was recognized as a CLEAN artifact. In fact it could not be found neither in the WENSS nor in the NVSS catalogue.

This paper is the second of a series describing the multifrequency properties of the B3-VLA sample. In the first paper we presented the radio continuum data at 10.6 GHz obtained with the Effelsberg radio telescope (Gregorini et al. 1998, hereafter Paper I). We detected 99$\%$ of the radio sources, with a typical flux density error of about 1 mJy for the fainter ones.

Here we present the spectral database of the whole sample consisting of flux densities at 151 MHz, 327 MHz, 408 MHz, 1.4 GHz, 4.85 GHz, and 10.6 GHz. Additional observations were performed for 478 sources at 4.85 GHz, which were necessary to complete the information at this frequency and to measure also at 4.85 GHz the polarization detected at 10.6 GHz.

Section 2 describes the observations and data reduction at 4.85 GHz. In Sect. 3 we present the database, with an accurate description of the method used to obtain the flux densities and the errors at each frequency. In Sect. 4 the data table is presented with a discussion of the data quality.