Galspect is one of several digital backends for the ALFA receiver at the Arecibo radio telescope. ALFA is a 7-beam, dual polarization L-band receiver. ALFA has a 300 MHz bandwidth, it is cooled to about 15K and has very good noise characteristics. Here is a picture of ALFA on a test stand without horns prior to installation in the telescope:
The radio telescope is quite large.
Galspect is a rackmount box in the control room next to the dish. The box is an 8-slot Compact-PCI chassis. The box contrains an off-the-shelf x86 CPU board and 7 custom boards using Xilinx Virtex-2 FPGAs, one board for each beam of the ALFA receiver.
For each polarization of each beam, Galspect does a 512-point frequency transform over 100MHz and an 8k point transform over 7.14MHz usually centered near 1420MHz for the study of galactic hydrogen.
The FPGAs and operation software provide many configuration options for filtering and mixing to optimize for the goals of a particular observation.
The galspect box runs Linux on the CPU board. It boots from a compact flash card and uses the flash card as the root filesystem. The cpu board loads the firmware into the FPGA boards and runs a monitor program to manage data collection.
Galspect runs with a fixed integration time of 1s, so the data rate is relatively modest, less than 1MB/s. The CPU board collects the integrated spectra from the FPGA boards stores them in FITS files over NFS.
Galspect was commissioned in the fall of 2004. The software was last updated in July of 2005. The spectrometer is currently being used in a number of ongoing survey projects.
This pages contains the FPGA designs and all of the software for the CPU.