We present radio interferometric observations of the EA2 Algol-type binary
system V505 Sagittarii made with the ATNF Compact Array at 6 and 3.6 cm ove
r one orbital cycle (1.18 d). We have obtained a strong detection of the so
urce (1.5 mJy at 6 cm and 1.4 mJy at 3.6 cm) and derive a brightness temper
ature for the emitting region of T-b similar to 2.7 x 10(9) K, a magnetic f
ield strength of 17 < B < 170 G and an electron density of N-e similar to 3
.7 x 10(8) cm(-3). The radio flux density levels show a clear modulation wi
th evidence of eclipses of the emission region at both conjunctions of the
binary. The form of the light curve implies that the radio source involves
at least some enhanced emission in the intra-binary region. This has import
ant consequences for the details of coronal formation and field interaction
in active close binary stars. We discuss some scenarios for the formation
of intra-binary active regions in Algol-type binary systems.