Application of IVOA software tools for radio sources investigation Zhelenkova O., Kopylov A., Chernenkov V. The interrelationship between the objects of astronomical catalogs in the different ranges of electromagnetic spectrum and their association into the real astrophysical source has obvious scientific interest. ... We used NVSS as the reference coordinate catalog. ... For 60% of radio sources identified with the objects of the radio catalogs we discovered optical candidates in SDSS survey. ...