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ALMA MEMO #422
The Dual-Load Calibration device revisited
S.Guilloteau (IRAM/ESO)
2002/05/23
Keywords: Receiver, Calibration, Atmosphere
Following ALMA memo 371, I re-investigate the dual load calibration scheme which has been proposed for ALMA. This memo improves on the requirements derived in memo 371 by using a better prediction for the atmospheric fluctuations at short time scales. It is shown that because of atmospheric properties and of the antenna geometry, a dual-load system located in the ALMA antenna subreflectors needs to switch at a rate in excess of 20--30 Hz to be efficient in the submillimeter regime. Moreover, integrations in excess of 10 seconds are required to get sufficient calibration accuracy at these frequencies. Because of the exceedingly high rate, and since the system has not been demonstrated to allow an absolute calibration, it is proposed to abandon this development.
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Last modified: 2002-05-29
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