From awootten at nrao.edu Thu Oct 14 10:23:28 2004 From: awootten at nrao.edu (Al Wootten) Date: Thu, 14 Oct 2004 10:23:28 -0400 Subject: [asac] ASAC Telecon Tuesday 19 October 2004 Message-ID: <16750.35808.790909.287796@polaris.cv.nrao.edu> Folks, As agreed at the face to face meeting, the next ASAC telecon is upon us. Conference Date: 2004-October-19 (Tuesday) Here's the dial-in information for the telecon: CALL TIME: 1030 am EDT or 14:30 UT CALL DATE: 19 October-2004 (Tuesday) DURATION: 1 hr * USA Number: 877-874-1919 * Outside USA Number: +1-203-320-9891 * Passcode: 185064 * Leader: Al Wootten Agenda is at: http://www.cv.nrao.edu/~awootten/mmaimcal/asac/asacoct04agenda.html Clear skies, Al +--------------------------------------------------------+ | Alwyn Wootten (http://www.cv.nrao.edu/~awootten/) | | Project Scientist, Atacama Large Millimeter Array/US | | Astronomer, National Radio Astronomy Observatory | | 520 Edgemont Road, Charlottesville, VA 22903-2475, USA | | (434)-296-0329 voice Help us build The ALMA| | (434)-296-0278 FAX {> {> {> {> | +----------------------------------^-----^-----^-----^---+ From soliver at nrao.edu Mon Oct 4 20:37:05 2004 From: soliver at nrao.edu (Stacy Oliver) Date: Tue, 05 Oct 2004 00:37:05 -0000 Subject: [asac] [almanews] ALMA Memo 505 Released Message-ID: <200410042206.i94M6MEI017971@orval.tuc.nrao.edu> ALMA Memo # 505 Bandpass Calibration for ALMA A. Bacmann (ESO), S. Guilloteau (IRAM/ESO) 2004-09-30 Keywords: Calibration, Bandpass This memo contains a detailed evaluation of the expected performance of the bandpass calibration for ALMA. We evaluate the limitations on the bandpass accuracy due to the imperfect knowledge of the atmospheric transmission. We show that the best bandpass accuracy is obtained when the amplitude calibration is applied in a single-load scheme. The proposed scheme is a variant of the so-called bandpass normalization technique. It uses normalization by the difference between the sky emission and the load emission, rather than normalization by the auto-correlation spectrum in the usual case. Bandpass calibration should be performed at the observing frequency. It will be limited by the knowledge of the sideband opacity difference. This knowledge can be based on a model, but a direct measurement is also possible, although time consuming. The bandpass calibration must be performed on strong point-like sources, of known spectral index. The knowledge of the spectral indexes will be a limiting factor in the wide band modes. Building up a database of suitable sources will be necessary, since the knowledge of these spectral indexes could be improved by bootstrapping techniques among several sources. Since astronomical sources have to be used, the required integration time varies substantially as a function of frequency. High accuracies can be reached in a minute of time at mm wavelengths, but integration time as large as an hour can be needed at sub-mm wavelengths. Occasional direct measurements of the sideband opacity difference could also be used to improve the accuracy of the atmospheric modelling. View a pdf version of ALMA Memo #505. http://www.alma.nrao.edu/memos/html-memos/alma505/memo505.pdf -------------- next part -------------- An HTML attachment was scrubbed... URL: -------------- next part -------------- _______________________________________________ Almanews mailing list Almanews at listmgr.cv.nrao.edu http://listmgr.cv.nrao.edu/mailman/listinfo/almanews From soliver at nrao.edu Mon Oct 4 20:37:35 2004 From: soliver at nrao.edu (Stacy Oliver) Date: Tue, 05 Oct 2004 00:37:35 -0000 Subject: [asac] [almanews] ALMA Memo 483 Released Message-ID: <200410042206.i94M6PEI017976@orval.tuc.nrao.edu> ALMA Memo # 483 The ALMA 1st Local Oscillator Reference Bill Shillue, Sarmad AlBanna, and Larry D'Addario National Radio Astronomy Observatory 2004-09-29 The ALMA 1st LO Reference system consists of a laser synthesizer, active line length correction, photonic distribution, and a photonic receiver. The phase stability and phase drift specifications are very ambitious, and the effort to meet them has led to small evolutions and improvements in the design. This memo gives a general description of the system, and documents its current measured performance levels, as measured in the laboratory. View a pdf version of ALMA Memo #483. http://www.alma.nrao.edu/memos/html-memos/alma483/memo483.pdf -------------- next part -------------- An HTML attachment was scrubbed... URL: -------------- next part -------------- _______________________________________________ Almanews mailing list Almanews at listmgr.cv.nrao.edu http://listmgr.cv.nrao.edu/mailman/listinfo/almanews