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A. Wolter (Osservatorio Astronomico di Brera, Milano, Italy), A. Celotti (Sissa, Trieste, Italy)
We construct the first X-ray selected sample of radio-loud quasars from the EMSS survey, and we compare spectral and statistical properties of the sample with those of other classes of blazars. The X--ray selection allows us to explore the properties of radio--loud quasars 10--100 weaker than classical samples in the radio band. There are no radio--loud quasars whose synchrotron peak reaches the UV--soft X--ray band at these (radio) flux levels (as occurs for BL Lac objects selected in the X--ray band), but they appear to have comparatively stronger optical--UV emission. We suggest that this can be ascribed to a significant contribution from a quasi--thermal optical--UV component, emerging due to the comparatively weak non-thermal emission. The detection of sources at low radio fluxes also shows the presence of a large population of steep spectrum quasars, and the lack of the predicted turnover in the quasar counts.