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Single Continuum
This allows a maximum-bandwidth setup to be defined using only a single receiver band or frequency. Upon choosing a band, the OT will automatically set the spectral window frequencies to recommended defaults, such that the sensitivity is maximised. In Band 6, this involves avoiding the inner portions of the sidebands as these are somewhat (
20 per cent) noisier. See the Technical Handbook for more details. In receiver bands other than 9 and 10, two spws are placed in each sideband, whilst B9 and 10 have all 4 spws placed in the same sideband. It is possible to change the absolute positions of the spectral windows by changing a single parameter, the average frequency of the setup, but the relative separations remain the same. A low-resolution correlator mode (TDM) is chosen for each spectral window.
- Receiver Band: Selecting a band will set up default spectral window frequencies. Only bands 3, 6 and 7 are available if full polarization has been selected.
- Sky Frequency: This is the average frequency of the defined spectral windows and more-or-less corresponds to the value of the first local oscillator (LO1). There is a default for each band, but this can be changed here by entering a frequency in the observed (sky) frame. It is possible to reset to the band default frequencies using the button provided.
- Rest Frequency: The rest frequency corresponding to the sky frequency is displayed for reference only. It corresponds to whichever source has been selected in the Targets table at the bottom of the Spectral Setup page.
The value of the Representative Frequency is displayed below the table of spectral windows. Its value will default to the centre of the chosen spectral window, but can be changed to another frequency within that spectral window if the transition of greatest interest is not at the centre.
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The ALMA OT Team, 2016 Aug 23