Compact Structure in FIRST Survey Sources

We present preliminary results from a statistical survey of compact structure in faint radio sources. Around 1000 sources from the VLA FIRST survey (flux densities larger than 1 mJy at 1.4 GHz) have been observed with the single-baseline interferometer Effelsberg-Arecibo. We observed each source, selected from a narrow strip of sky at declination 28 deg, for just one minute. The baseline sensitivity at 1.4 GHz, using 512 Mb/s recording, is such that any FIRST source, selected at random, would be detected if most of its flux density is in compact structure. We discuss the detection-rate statistics from one epoch of these observations.