Astronomical FFT processing system
This document describes the Astro FFT processing system as designed and
developed by Alpha Data Ltd and BEAM Ltd in conjunction with Bristol
The purpose of the system is to process a 23 Mhz bandwidth signal and
a power spectrum averaged over time. This allows a coherent signal
to be brought out of a relatively large amount of noise.
The system processes two separate analogue signals, normally two
polarization's, with a 0 to 23 MHz bandwidth. The system then
in real-time, performs a 4096 point FFT on each signal and averages the
resultant power components over time. The resulting averaged power
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
in a 19 inch rack unit. The main FFT processing is performed by two
Virtex FPGA based PCI boards each of which has twin 14 bit analogue to
System Software Overview
The system software is based upon the Linux operating system. This
a full multitasking, networked operating system allowing access to the
AstroFFT system from other systems on a local network. The system can
be run as a stand alone box on the network with no keyboard, mouse or
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.
The Linux system installed is RedHat 7.2. This is a full installation
all of the applications for a full Linux workstation and software
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
On power up the system starts off the various system daemon processes
the AstroFft processing daemon.
- AstroFFT: The astro processing daemon. Remote applications can
to this service to control the Astro FFT processing system.
- NFS: The NFS network file system protocol is supported allowing
to access the /data directory on the system in read only mode.
- SMB: The SMB, Microsoft Windows network file system,
supported allowing access to the /data directory with read only
as the astro user.
The AstroFft Daemon
This is the main control application of the Astro FFT processing
This software process runs as a real-time process and is responsible
managing the FPGA hardware FFT engine, real-time post processing the
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
It connects to and controls the AstroFFT daemon. More information is in
the AstroGui User Manual
The Astro FFT system processes two separate signal sources. Normally
signal sources are the two, mixed down, signal polarization's received
from the dish antenna. Each signal is processed by an FPGA based
engine. Each FPGA based processing engine has two analogue input 14 bit
samplers operating at 50 MHz each with an anti-aliasing filter. This
the FFT engine to operate with a quadrature signal source to improve
resolution. More information on the signal processing is in the System
FPGA Board Documentation