The S2 baseband processing system for phase-coherent pulsar applications

Abstract

The S2 baseband processing system (S2-BPS) is designed for a variety of pulsar measurements such as ultrafast signal fluctuations and pulse timing. Its key features are: the S2 recorder; the S2 Tape-to-Computer Interface (S2-TCI) which provides an efficient high data rate transfer from S2 tapes to computer; and the tightly coupled control interface to the computer which enables automated data transfer and processing. Developed originally for VLBI applications, the S2 recorder is based on the use of commercial VHS tape transports (VCR's), modified for use in digital high density, high data rate applications. A single S2 recorder tape-set of eight SVHS tapes provides up to 500 GBytes of data storage, and an unattended operating time of up to 8.5 hours at the maximum data rate of 128 Mbits/s or 16 MBytes/s, corresponding typically to 16 MHz bandwidth in two circular polarizations at 2-bit quantization, which generates a data rate of up to 1 GByte/minute. With 16 MHz individual record channels, a single S2 yields a sample time resolution of 31 ns. For more challenging applications, multiple S2's may be used for increased bandwidth and higher time resolutions. In this paper, we present an overview of the S2 baseband processing system and plans for future implementations of the system, and demonstrate first results of Vela pulsar recordings at Parkes in September 1995. We pay specific attention to the S2-TCI, a system designed to transfer S2 recorded data from tape to computer memory (RAM) via direct memory access (DMA). Computer data may be processed locally or sent to a more powerful remote (super) computer for processing.