Enhanced fast Fourier transform application aids radio astronomy

May 09, 2016 // By Graham Prophet
Keysight Technologies recently introduced an improved version of its FFT option for the U5303A PCIe 12-bit high-speed data acquisition card. This card features two channels and a sampling rate from 1 Gsample/sec to 3.2 Gsample/sec, yielding bandwidth of DC up to 1.4 GHz, and resolution of 97 kHz per spectrum line.

It features, the company adds, greatly improved fixed point arithmetic and is aimed at applications in astronomy, physics and environmental measurements. While providing continuous real-time FFT at full sampling rate, this option also enables spectra accumulation capability, a key requirement for radio-astronomy. The image shows a radio astronomy signal capture; specifically, a “Solar burst with ‘tilted fibres’” observed with a 12-bit 12-bit PCIe digitizer plus FFT option, by Keysight Technologies, taken at the Radio Astronomy Observatory of ETH Zürich, Switzerland.


With DC up to 2 GHz bandwidth nominal, the card converts even low frequencies of around 0 Hz not observable with an AC front-end; moreover, AC coupling would introduce BF noise, whereas DC coupling provides measurement fidelity. By increasing the resolution from 8- to 12-bit, this option provides computation of a 32k points FFT for single or dual channels. Low-noise capabilities allow users to detect phenomena difficult to observe, such as tilted fibres (a phenomenon associated with flux lines in the sun’s corona) in a solar burst.


Additionally, in a controlled environment, this application can run at altitude of 15,000 feet.


Key features of the new FFT version include:

- Single and dual channel mode selectable on-the-fly

- High-speed FFT on 32,768 data values computed in 10.24 μsec at 3.2 Gsamples/sec

- Input bandwidth up to 1.4 GHz at 3.2 Gsamples/sec, resolution of 97.66 kHz per spectral line

- Highly improved fixed point arithmetic that eliminates deteriorating effects


Key advanced functionalities include:

- Sideband separation for I/Q mixers with full amplitude and phase error correction

- High number of accumulations: greater than 1,000,000 power spectra

- No dead time in the accumulation process

- Filter bank extension for superior channel separation without any drawbacks


"Thanks to a remarkable dynamic range, this new fast Fourier transform version allows performance of sensitive observations in highly interfered environment," said C. Monstein, Radio Engineer at Institute for Astronomy, ETH