The Next-Generation of Fast Fourier Transform Spectrometer (FFTS)
B. Klein, I. Kraemer, S. Hochguertel, R. Guesten, A. Bell and K. Meyer Max-Planck-Institute for Radioastronomy, D-53121 Bonn, Germany
We present our second generation of broadband Fast Fourier Transform Spectrometers (FFTS), developed for radio astronomical applications at the MPIfR. We have developed new analyzer boards, making use of the latest version of giga-Hertz analog-to-digital converters and the most complex FPGAs commercially available today. These state-of-the-art chips have made possible to build a digital spectrometer with a monolithic bandwidth up to 1.8 GHz and 8192 frequency channels. To simplify the combination of many analyzer cards into an Array-FFT Spectrometer (AFFTS), the novel board includes a complete 100 Mbit/s Ethernet interface. Precise time stamping of the processed spectra is realized by an on-board GPS/IRIG-B time decoder. The compact FFTS board (100 x 160 mm) operates from a single 5 Volt source, includes a flexible ADC clock synthesizer, and dissipates less than 20 W. Unlike the conventional windowed-FFT processing, a more efficient pre-processing algorithm has been developed with significantly reduced frequency scallop loss, less noise bandwidth expansion, and faster sidelobe fall-off. The new spectrometer board, which is now commercial available, has been field-tested at the APEX telescope and we present a first 1.5 GHz spectrum as observed in October 2007. Finally, we provide an outlook to our on-going developments.