SERENDIP 5 Spectrometer Board for SETI and Radio Astronomy

Henry Chen, Jeff Mock, Aaron Parsons, Wonsop Sim, and Dan Werthimer
Space Sciences Laboratory SETI Group, University of California, Berkeley

The SERENDIP 5 spectrometer board was designed for applications in SETI, FX correlators, pulsar, and general radio astronomy.

Each spectrometer board processes two polarizations, each polarization with up to 128 MHz bandwidth and 64 million channels. The CompactPCI board utilizes four 200 MHz 8-bit ADC's for analog input, and 176 digital I/O lines for optional digital input and/or fast readout. The signal processing is implemented in a Xilinx Virtex-II Field Programmable Gate Array (FPGA) chip (XC2V4000 or XC2V6000), which can be dynamically programmed for various applications. A smaller additional Xilinx FPGA (XC2V1000) is used as a reconfigurable backend processor which can pass data off to an independent computer.

The spectrometer uses a polyphase filter bank (PFB) to implement a bank of steep cut-off bandpass filters, providing a significant improvement in signal-to-noise and out-of-band-rejection over the common FFT algorithm. The PFB uses a biplex pipelined architecture which allows data to be input and output at the full sample rate, and can do two polarizations simultaneously with no extra cost in hardware or data flow rate.

SERENDIP5-based spectrometers are currently in use at Arecibo, Greenbank, and ATNF for pulsar, epoch of reionization and galactic hydrogen surveys. The upcoming SERENDIP V SETI sky survey will utilize Arecibo Observatory's seven-beam L-band feed array and 21 spectrometer boards for a 2.7 billion-channel instrument. The JPL SETI sky survey plans to use 200 of these boards to cover 20 GHz band with 25 billion channels. The Allen Telescope Array will soon be using the spectrometer boards in the FX correlator. We hope others will find these boards or the FPGA-based spectrometer designs useful.