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Spectral Scan

A spectral scan is defined by entering a start and stop frequency, in the observed/sky frame only, as well as the correlator mode that should be used (bandwidth $\ge$ 500 MHz). Using these parameters, the OT will then attempt to cover the requested frequency range using a maximum of five tunings. In general, the OT will not be able to cover the exact requested frequency range, perhaps because this might require more than 5 tunings, but also because it always uses the maximum available four spectral windows per tuning. Spectral averaging is available for the high-resolution modes, but will be the same for each spectral window of each tuning.

As you would expect, the tunings are placed side-by-side, the only real complication being that for modes that require two sidebands, the lower sideband of tuning $n+1$ must be placed in the gap between the sidebands of tuning $n$. This is unavoidable and leads to non-uniform sensitivity in the final spectrum, but the requested sensitivity will be achieved everywhere. Since Cycle 3, small overlaps are assumed, both between the spectral windows of a tuning, and between tunings. This ensures that the edge channels that are most likely to be affected by technical problems are excluded.

The best way of seeing how the spectral windows are placed is by using the Spectral Visual Editor. Spectral windows corresponding to the same tuning are plotted with the same $y$-offset and displayed with the same colour. Also shown is the requested frequency range for easy comparison with the actual frequency coverage.


next up previous contents
Next: Multiple velocities and tuning Up: Spectral Setup Previous: Single Continuum   Contents
The ALMA OT Team, 2016 Aug 23