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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.
|Band width [MHz]||1000||500|
|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.
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.
LOcommand before using the
SPECTROMETERcommand to set the bandwidth or the IF offset.
UIP> SPECTROMETER /FFTS1W
UIP> SPECTROMETER /FFTS1N
UIP> SPECTROMETER /FFTS1W 5.75
UIP> SPECTROMETER /FFTS1N 1.25
UIP> spec /ffts1w 1.5+0.005
The FFTS1 sometimes overheats during longer observations, with long integration times or many subscans or repetitions.
^Cin the UIP to abort the observation.
UIP> SPECTROMETER /FFTS1W /RESTART
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.
^Cin the terminal window within the VNC desktop to kill the running server.
./startWOLA(we are using the WOLA core instead of the regular windowed FFT core).