The AOFTM is an Observatory-Owned fast-dump spectrometer whose number of channels and time resolution are programmable with up to 1024 bins across a 10-MHz bandwidth. It has been specifically designed for pulsar searches with the 430-MHz feed. The AOFTM channels two IF signals to baseband, then digitizes and Fourier analyzes the signal, with on-the-fly normalization of the spectra for each of its 16 spectrometer boards. It then co-adds the two polarizations and packs the samples into two bits before writing the power spectra to the SPARCstation RAM.
The PSPM is the first User-Owned Public-Access pulsar backend. It is currently engaged in the five on-going upgrade-period pulsar searches with the 430-MHz feed. The PSPM is a filter bank that accepts two polarizations through 2 x 128 channels with 60 kHz per channel. It is suitable for ultrafast searches (80-ms sampling) and high-precision timing (12-ms sampling).
The Princeton Mk-III processor is a User-Owned Public-Access instrument capable of averaging pulsar signals passed by the Observatory filter banks. Reticon pre-detection dedispersion capabilities with the Mk-III are no longer supported. However, software is available for real-time display and for preliminary data reduction.
The Princeton Mk-IV system is designed for fast recording of coarsely quantized baseband data. It presently provides either 10-MHz sampling of four analog channels at 2 bits per sample, or 5-MHz per channel at 4 bits. The system produces some 36 GB of data per observing hour, which requires more than a gigaflop of computing capability for reduction. During its first year or so, and while under testing, this instrument will remain in the User-Owned category.
During the first week of December 1996, the installation of the ABPP will take place. This is a coherent-dedispersion digital processor that allows the nominal bandwidth used to be automatically configured such that, after dedispersion of the pulsar signals, the highest possible effective time resolution is obtained for the observing frequency used. The dispersion is removed by convolution of the baseband signal with a 1024-tap FIR filter, which is a fully customized VLSI chip designed and built at Berkeley.
Following requests from the pulsar community expressed at the Arecibo Pulsar Workshop held in October 1995, NAIC plans to construct a Modular Post-detection-correlation Signal Processor (MPSP) based on the NAIC 1024-lag correlator chip. Designed for the needs of Arecibo pulsar research, this instrument will make use of the new capabilities offered by the Gregorian configuration. The processor will satisfy both folding (synchronous sampling) and search mode requirements, and will facilitate fast dumping, as well as pulse windowing for an effective single-pulse mode.
The MPSP will be built in two phases. A prototype 16-chip unit will provide up to 50-MHz bandwidth with full Stokes polarimetry and 9-level sampling. Narrower bandwidths in octave steps down to 200 kHz will be provided using digital filters. It will also produce i) 100-MHz bandwidth, full-Stokes data with 3-level sampling, ii) a pair of 100-MHz bandwidth, dual-polarization channels, or iii) 400-MHz bandwidth in four independently tunable 100-MHz bands for a single polarization. In a second development phase, three additional 16-chip units (without the digital filters) will provide total bandwidths of up to 800 MHz for dual polarizations. The processor will provide a time resolution of 20 ms with 1024 frequency lags, and will provide higher time resolution with fewer lags. A PostScript file of a more detailed description of the processor is at http://www.naic.edu/~kiriaki/MPSP.ps. The first module is expected to be completed by the end of 1997.
A continuum polarimeter is also under construction. This analog device will initially have 250-MHz filters in front of each of its four units. The time constants chosen for this machine are to be short enough to allow pulsar observations at high frequencies where use of wide bandwidths are essential. This device is expected to be available to users in 1997.
The upgrade-period drift-scan pulsar searches have been resumed, with initial reestablishment of procedures in October 1996, and are proceeding from where they were discontinued in February 1995 when pointing capabilities ceased to be available. Following a limited evaluation of the 430-MHz pointing, we were sufficiently confident of our understanding of the pointing situation to be able to restart the searches. Searching, though far from a trivial matter for our daily operations, is now regularly scheduled for the five upgrade-period projects.
The data-taking hardware used for the searches is the PSPM filter bank (see above). The bandwidth used is 8 MHz and the sampling is 80 ms. The 4-bit packed data are striped onto two recorders, which fill about 10 Exabyte tapes per night.
Copyright 1996, Cornell University
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