Table of Contents

Fast Fourier Transform Spectrometer (FFTS1)

Developed for the CSO by the Max-Planck-Institut für Radioastronomie (MPIfR), the Fast Fourier Transform Spectrometer (FFTS1) is available with all the heterodyne receivers. This spectrometer has two modes, wide (1000 MHz) and narrow (500 MHz) band. The FFTS1 can be operated simultaneously in parallel with the other spectrometers, i. e., FFTS2 and AOS5.

FFTS1 Specifications
Mode Wide Narrow
Band width [MHz] 1000 500
Channels 8192
Channel spacing [kHz] 122 61
Noise bandwidth [kHz] 117 58
Signal processing 4 tap WOLA with flat top window

The FFTS1 accepts 4-8 GHz input signals from the wide (4 GHz) band receivers directly. With these receivers, the FFTS1 band can be placed anywhere within the receiver IF band. With the narrow (1 GHz) band receivers, a separate IF processor upconverts the IF band to 6-7 GHz.

The temperature calibration (TCAL) scheme for the FFTS1 takes advantage of its high dynamic range. The input IF signal level is adjusted on the sky before the TCAL scan. (For the 230 GHz receiver, an extra 3 dB attenuation is added during integrations on the ambient temperature load and sky). By contrast, for the AOS5 the input IF signal level is adjusted on the ambient temperature load before the TCAL scan and then is readjusted on the sky after the calibration.

The TELESCOPE identifier in the CLASS header is CSO FFTS 1W or CSO FFTS 1N for the wide (1000 MHz) or narrow (500 MHz) band mode, respectively.

UIP commands

IF processor

To use the FFTS1 with the narrow band receivers, the IF processor must be turned on. The switch is near the top right of the AOS5 rack in the laboratory.



The FFTS1 sometimes overheats during longer observations, with long integration times or many subscans or repetitions.

Occasionally, FFTS1 gets stuck in a failure mode where it takes twice longer to integrate, or it will not integrate at all. To solve this problem, restart its server program.