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Sideband Filter

A new and experimental Sideband Filter restricts the list of available lines based on the lines that havealready been selected. The default behaviour of the sideband filter isdifferent depending on whether you have launched the Spectral LineSelection Tool for selecting or overlaying lines. If you are choosinglines to enter into the spectral window table, the filter is enabled by default. If you are overlaying lines, the filter is disabled by default. As this is a new feature, it can be disabledusing a checkbox. We now briefly explain how this filter works.

An ALMA receiver has two sidebands with fixed widths and separations- all of the defined spectral windows must fit into the sidebands asonly then can a tuning solution be found. Entering a single linedefines a range of frequency space where other lines could beadded. For example, if the OT has automatically placed this line inthe upper sideband, the available frequency space will not onlyinclude the lower sideband, it will also include what would have beenthe upper sideband had the OT instead placed the line in the lowersideband! Once a second line is defined that sits in one of thepossible other sidebands, the ``third'' sideband disappears. Ingeneral, as more lines are defined, there is less and less freedom asto where additional lines can be placed. Note that if the first linedefined is close to the edge of an ALMA band, the ``third'' sidebandwill never arise as the line can only go in the upper or lowersideband.

We again note that this is an experimental feature that has not beentested as much as we would like. We hope that it will be useful, butplease be careful when using it.


next up previous contents index
Next: The Phase 1 Observing Proposal Up: Spectral Line Selection Tool Previous: Spectral Line Selection Tool   Contents   Index
The ALMA OT Team, 2011 May 20