The Parkes 21 CM multibeam receiver

Several extragalactic HI surveys using a 21-cm 13-beam focal plane array will begin in late 1996 using the Parkes 64-m telescope. These surveys are designed to detect efficiently nearby galaxies that have failed to be identified optically because of low optical surface brightness or high optical extinction. We discuss scientific and technical aspects of the multibeam receiver including astronomical objectives, feed, receiver and correlator design and data acquisition. A comparison with other telescopes shows that the Parkes multibeam receiver has significant speed advantages for any large-area 21- cm galaxy survey in the velocity range range 0 - 14000 km per sec.