Astronomical FFT processing system

Introduction

This document describes the Astro FFT processing system as designed and developed by Alpha Data Ltd and BEAM Ltd in conjunction with Bristol University. The purpose of the system is to process a 23 Mhz bandwidth signal and generate a power spectrum averaged over time. This allows a coherent signal spectrum to be brought out of a relatively large amount of noise.

A typical installation

The system processes two separate analogue signals, normally two signal polarization's, with a 0 to 23 MHz bandwidth. The system then continuously, in real-time, performs a 4096 point FFT on each signal and averages the resultant power components over time. The resulting averaged power spectra are stored in data files that can be used for further data analysis.

System Hardware Overview

The system hardware consists of a dual Pentium processor based system housed in a 19 inch rack unit. The main FFT processing is performed by two Xilinx Virtex FPGA based PCI boards each of which has twin 14 bit analogue to digital convertors.

System Software Overview

The system software is based upon the Linux operating system. This provides a full multitasking, networked operating system allowing access to the AstroFFT system from other systems on a local network. The system can either be run as a stand alone box on the network with no keyboard, mouse or display or as a fully fledged Linux workstation.
The Astro FFT software itself, consists of two main applications: the AstroFft daemon and the AstroGui user interface.

Astro FFT system

Software Operation

The Linux system installed is RedHat 7.2. This is a full installation with all of the applications for a full Linux workstation and software development platform. This allows the system to be used as a full Linux workstation as well as a simple network resource.
The Linux system has networking enabled and provides the following network resources: On power up the system starts off the various system daemon processes and the AstroFft processing daemon.

The AstroFft Daemon

This is the main control application of the Astro FFT processing system. This software process runs as a real-time process and is responsible for managing the FPGA hardware FFT engine, real-time post processing the FFT data, data storage and system control.
It is controlled by commands sent over a network control socket from either the local AstroGui control process or a remote control process.
More information on the Astro FFT process is in the; AstroFft Software API .

The AstroGui User Interface

The AstroGui application provides a user with the means to control the data acquisition and logging parameters of the Astro FFT processing system. It connects to and controls the AstroFFT daemon. More information is in the AstroGui User Manual .

Signal Processing

The Astro FFT system processes two separate signal sources. Normally these signal sources are the two, mixed down, signal polarization's received from the dish antenna. Each signal is processed by an FPGA based processing engine. Each FPGA based processing engine has two analogue input 14 bit samplers operating at 50 MHz each with an anti-aliasing filter. This allows the FFT engine to operate with a quadrature signal source to improve FFT resolution. More information on the signal processing is in the System specifications Manual.

User Information

System Information

FPGA Board Documentation

Misc

Contacts


 

BEAM Ltd's Web Site http://www.beam.demon.co.uk
BEAM Ltd's support support@beam.demon.co.uk
Alpha Data's web site http://www.alphadata.co.uk
Alpha Data email address info@alphadata.co.uk