The Westerbork Northern Sky Survey

The Westerbork Northern Sky Survey (WENSS) is a low-frequency radio-survey that covers the whole sky north of $\delta$ = 30$^\circ$ at a wavelength of 92cm to a limiting flux density of approximately 18mJy [50]. The WENSS comprises two source catalogues: the main catalogue contains 211234 sources in the declination range 28$^\circ$ $< \delta <$ 76$^\circ$ (83134 in the FBS area); the polar catalogue contains 18186 sources above 72$^\circ$ (12239 in the FBS area). The positional accuracy ranges from 1$.\!\!^{\prime\prime}$5 for the brighter sources to 10$^{\prime\prime}$ for the weakest. The source surface density is about 23 deg^-2. The total number of coincidences within 1$^\prime$ with FBS objects not known to be stars is equal to 19 (including eight known QSOs), while 15 are expected by chance. The distances between optical and radio positions for the eight QSOs are all smaller than 20$^{\prime\prime}$; for the unclassified objects, the smallest distance is 34$^{\prime\prime}$, suggesting that no new QSO has been detected.