UCB/JPL SETI Spectrometer System Description

Introduction

The UCB/JPL SETI Spectrometer is a joint development between the UC Berkeley SETI Group, the Berkeley Wireless Research Center (BWRC), and the NASA Jet Propulsion Laboratory (JPL). It is deployed at DSS-13, Venus Station, of NASA's Goldstone Deep Space Communications Complex. The system is based on a BWRC BEE2 (Berkeley Emulation Engine) general-purpose high-end reconfigurable computional platform.

System Specifications

• Receiver: 2275MHz
• IF Feed: Single polarization, 154MHz centered at 267MHz; -3dB at 190MHz and 344MHz
• Digitization: 800Msamples/sec, I/Q output
• Baseband: 200MHz bandwidth, dowmixed at 275MHz, with 4x decimation
• System clock frequency: 200MHz
• Coarse channelization: 4096 @ 48.8KHz ea.
• Fine channelization: 32768 per coarse channel @ 1.49Hz ea.
• Processing rate: 1 128Mchannel spectrum every 0.67 sec.

System Description

The spectrometer's system architecture and dataflow is shown in Figure 1. Data from the antenna IF is digitized on the ADC board at 800MHz, then serialized by the IBOB (InfiniBand Break-Out Board) and sent to the BEE2. Processing on the BEE2 is split into five stages, each of which occupy a separate FPGA (Field-Programmable Gate Array) on the board. The data is first mixed down to baseband and the data rate decimated in the digital downconverter (DDC), before being passed to the PFB (polyphase filter bank) for coarse channelization. A matrix transpose (the corner turner) between the PFB and FFT blocks allow each of the PFB frequency bins to be buffered and broken further into fine channels by the FFT. Frequency bins of interest are picked out by the thresholder, which compares each FFT bin power against a scaled coarse-bin average.