VLBI observations of 24 3CR CSS radio sources at 50 cm.

We present the results of snapshot observations carried out at 50 cm with a Global VLBI Network on 24 compact steep-spectrum sources (CSS) from the 3CR catalogue (3C43, 48, 49, 67, 119, 138, 186, 190, 216, 237, 241, 268.3, 287, 298, 299, 303.1, 305.1, 309.1, 318, 343, 343.1, 346, 380, 454). The angular resolution ranges from about 20 mas for the global data to about 100 mas for the local networks (EVN and/or EVN + USVN) only. The minimum measurable surface brightness ranges from ~10 to ~40 mJy/beam. Cores have been identified or confirmed in six sources (3C43, 186, 190, 216, 298, 346) through the spectral information contained in these observations. For radio components <~150 mas the new data allow the radio spectra to be evaluated down to 610 MHz. In general, no evidence is found for self-absorption, except in the radio cores. Data reduction techniques have been developed to deal with the poor UV coverage of snapshot VLBI observations.