A WIDE-BANDWIDTH DIGITAL RECORDING-SYSTEM FOR RADIO PULSAR ASTRONOMY

The study of radio pulsars at the highest time resolution is currently limited by the capability of the signal detection system to accept a wide-bandwidth signal, and to sample the data rapidly enough. We descr ibe a new instrument for pulsar research which utilizes baseband recor ding at 400 Mbit s(-1) to achieve bath a high bandwidth and a high sus tained data rate. The wide bandwidth digital recording (WBDR) system i s based on a custom analog/digital VLSI digitizer operating at 50 MHz, and a commercial digital cassette tape recorder. Signal analysis is p erformed entirely in software, using a massively parallel computer. Si nce we record a representation of the electric vector of the pulsar em ission, the instrument is very flexible, and the data can be analyzed in several modes in software. We can synthesize the software equivalen t of a conventional hardware filterbank, and we have implemented a ''c oherent dedispersion'' algorithm, which yields a sample time of 10 ns. The combination of a wide bandwidth and sustained data rate make this instrument a unique and powerful tool for pulsar astronomy. Our instr ument is particularly well-suited to searches for millisecond pulsars at low frequency, in directions where pulsed signals are strongly disp ersed by the interstellar medium. We present results based on dual-pol arization test observations in a 600 +/- 25 MHz band at the Owens Vall ey Radio Observatory 40-m Telescope.