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ALMA Memo #274

Reconfiguring the ALMA Array

Stephane Guilloteau [1]

September 13, 1999

Keywords: Configuration, Transporter, Sub-array

The sensitivity losses which result from configuration changes are investigated. It is shown that it is preferable to move a small number of antennas (typically 4) and re-calibrate their positions and pointing constants every day during the configuration change, rather than to attempt moving a large (16 -- 32) number before performing the calibration session.

This requires the ALMA to support a sub-array mode in which one sub- array can continue observations of a scientific program, while the other one is observing in continuum in the 3 mm or 2 mm band. Such a sub-array capability has design consequences in the local oscillator system for the antennas and the correlator.

If sub-arrays are not possible, the equivalent time loss due to a configuration change is about 31 hours for 2 transporters. In all cases, there is little gain in having more than 2 transporters.

[1] IRAM


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Last modified: 05 October, 1999

kweather@nrao.edu