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Baseband and Spectral Windows Configuration

On the right the panel Spectral Spec contains the frequency fields for the observation: the rest frequency of the line, the line identification and the receiver band. Other fields can also be defined but have no graphical representation in the graph.

The Switching and Correlator Configuration panels have already been discussed in Chapter  8.4.3 .

In a SpectralSpec up to four basebands can be specified using the Add Baseband button andwithin each baseband up to 32 spectral windows can be defined. In the field of the panel BaseBand Configurations the details of the baseband configuration(s) are displayed.

The top part of the this panel contains the information about the selected baseband configurations, followed by the baseband details. Each of the basebands can be displayed by selecting the corresponding tab. The lower part shows the information with the specifications of the spectral windows that are specified for this baseband configuration. Each of the windows can be displayed by selecting its tab.

By specifying the baseband central frequency field Centre Frequency in BaseBand Configurations and given the position of the LSB and USB (determined by the LO1 frequencyin the Setup Preferences panel) the user indirectly chooses whether the baseband will fall in the USB or the LSB. In the upper graphical display the vertical line and the bars indicate the position of the LO1 frequency and the positions and the bandwidths of the chosen baseband configurations.

Initially, the position(s) of the selected baseband configuration(s) will not be optimal within the LSB and USB. Also, as the LO2 frequency can only fall within certain ranges,the user defined LO1 setting (and hence the LSB and USB) may have to be adjusted in order to achieve the requested central baseband frequency. Since there is only one LO1 setting possible, in the case of multiple baseband specifications the LO1 and LO2 settings have to be optimised to get closest to the requested centre baseband frequencies. The SpectralEditor provides the functionality to do the optimisation.

In the panel LO Setup Preferences in the form on the right, the checkboxes for Sideband(s) to prioritise allow you to select a sideband that is to be given priority in the LO optimisation. It is also possible to assign priorities to basebands using numeric values between 0 and 100 in the Base band(s) config to prioritise section. Pressing the Calculate LOs button will calculate the LO setup according to the chosenparameters.

The best setup (in terms of LO1 and LO2 settings) for a single or multiple baseband configuration is determined by calculating the error between the ideal and the adjustedLO2 setting for each of the basebands and minimising the sum of these errors. After clicking on the Calculate LOs button, a summary of the optimisation results can be seen in the Feedback pane, using the Information tab. Clicking on the expansion symbol \( >> \) provides details, including the ideal setting of the LO1 and LO2 frequencies, the frequency offsets given the system limitations in setting the LO2 frequencies and the adjusted LO1 and LO2 frequencies.


next up previous contents index
Next: Baseband Visualisation Up: The Visual Spectral Editor Previous: Receivers and LO Visualisation   Contents   Index
The ALMA OT Team, 2011 May 20