The sources presented here are drawn from a working list of CSS-GPS radio sources and candidates (Dallacasa & Stanghellini 1991) with the addition of a dozen of CSS quasars from Barthel et al. (1988) and from Wills (1979). They do not represent a complete sample. Most of the objects are high redshift quasars known to be unresolved (or marginally resolved) at arcsecond resolution.
The radio information on these sources is generally sparse, and their radio spectra have been built with a few points from observations spanning many years. This allows the inclusion of variable, flat-spectrum sources, appearing as GPS objects in case the high frequency data were acquired during a low state of radio activity. Therefore the integrated radio spectra presented here can be misinterpreted, particularly for the objects with very few measurements.