Detecting sub-mJy sources with the EVN

Some microquasars are permanently bright radio sources while others are faint but produce powerful radio outbursts. Most of the X-ray binaries (XRB) however are very faint or undetected in the radio regime. The European VLBI Network (EVN) recently introduced the Mark5 recording system which allows data rates of up to 1 Gbit s^-1. This increases the sensitivity of the array significantly. We briefly describe recent developments in the EVN in terms of reliability of the network and also data quality. We demonstrate the power of the EVN in detecting sub-mJy radio sources with modest integration times (order of hours). This high sensitivity capability will permit the study of variable Galactic sources at milli-arcsecond resolution. An estimate is given for the lowest detectable mass of hypothetical intermediate-mass black holes (IMBH) in nearby galaxies, provided these are located in radio-jet systems analogous to microquasars and active galactic nuclei.