From soliver at nrao.edu Fri Nov 1 15:55:57 2002 From: soliver at nrao.edu (Stacy Oliver) Date: Fri, 1 Nov 2002 13:55:57 -0700 Subject: [asac][almanews] ALMA Memos 439 and 440 Released Message-ID: ALMA MEMO #439 Millimetre Wave Generation Using an Optical Comb Generator with Optical Phase-Locked Loops Pengbo Shen and Phillip A. Davies, Dept. Of Electronics, University of Kent, Canterbury William P. Shillue, Larry R. D'Addario, and John M. Payne, NRAO 2002-10-31 Keywords: Comb Generator, Photonic, lasers, LO (This memo is also presented at the 2002 International Topical Meeting on Microwave Photonics, a conference in Awaji Japan, and also appears in the conference digest) We report the generation of millimeter-wave signals to 158 GHz with phase noise better than -75 dBc/Hz at 100 kHz offset, by heterodyning of two laser which are optically phase-locked through an Optical Comb Generator. View a pdf version of ALMA Memo #439. http://www.alma.nrao.edu/memos/html-memos/alma439/memo439.pdf Download a postscript version of ALMA Memo #439. http://www.alma.nrao.edu/memos/html-memos/alma439/memo439.ps ________________________________________________________________________________________________ ALMA Memo # 440 Photonic Techniques for Local Oscillator Generation and Distribution in Millimeter-Wave Radio Astronomy 10/31/2002 John M. Payne and William P. Shillue, National Radio Astronomy Observatory Keywords: photonic, LO, photomixer {Note: This memo was an invited talk at the 2002 International Topical Meeting on Microwave Photonics, a conference held in Awaji Japan, and also appears in the conference digest. It repeats some information that has already been presented in previous ALMA memos, and is included here in the memo series because the conference proceedings are not widely distributed} A number of photonics techniques are being used for Local Oscillator (LO) generation and distribution for millimeter-wavelength radio astronomy. Many of these are being implemented or considered for use on the Atacama Large Millimeter Array (ALMA) project. View a pdf version of ALMA Memo #440. http://www.alma.nrao.edu/memos/html-memos/alma440/memo440.pdf Download a postscript version of ALMA Memo #440. http://www.alma.nrao.edu/memos/html-memos/alma440/memo440.ps _______________________________________________ Almanews mailing list Almanews at listmgr.cv.nrao.edu http://listmgr.cv.nrao.edu/mailman/listinfo/almanews From awootten at nrao.edu Tue Nov 5 12:10:22 2002 From: awootten at nrao.edu (Al Wootten) Date: Tue, 5 Nov 2002 12:10:22 -0500 Subject: [asac]Meeting Tomorrow Message-ID: <15815.64382.637873.458379@polaris.cv.nrao.edu> Folks: Here's the dial-in information for the telecon: CALL TIME: 10:30 AM EASTERN TIME 1530 Universal Time (Follow the link for times in other time zones as various nations change to and from summer time) CALL DATE: 06-November-2002 (Wednesday) DURATION: 1 hr USA Toll Free #:888-810-4932 International #: +1-212-287-1626 PASSCODE: 35524 LEADER: Al Wootten This and the agenda may be located at: http://www.cv.nrao.edu/~awootten/mmaimcal/asac/asacnov02agenda.html Clear skies, Al From soliver at nrao.edu Mon Nov 4 16:06:11 2002 From: soliver at nrao.edu (Stacy Oliver) Date: Mon, 4 Nov 2002 14:06:11 -0700 Subject: [asac][almanews] ALMA Memos 438 Released Message-ID: ALMA Memo #438 Measurements of Materials for SIS Mixer Magnetic Circuits G. A. Ediss and K. Crady National Radio Astronomy Observatory 2002/11/01 keywords: magnetic materials, hysteresis measurements Measurements have been made of various magnetic materials in order to improve the flux density at the SIS junction positions in the mixer. The materials measured are Hiperco 50A, HyMu 80, Consumet iron and Magnet iron. Magnet iron is recommended for unannealed use. Consumet is recommended for annealed use. Hiperco 50A can be used annealed if large hysteresis can be accepted. For highest flux density for lowest drive current, annealed Consumet should be used. View a pdf version of ALMA Memo #438. http://www.alma.nrao.edu/memos/html-memos/alma438/memo438.pdf Download a postscript version of ALMA Memo #438. http://www.alma.nrao.edu/memos/html-memos/alma438/memo438.ps _______________________________________________ Almanews mailing list Almanews at listmgr.cv.nrao.edu http://listmgr.cv.nrao.edu/mailman/listinfo/almanews From wilson at physics.mcmaster.ca Wed Nov 13 12:15:44 2002 From: wilson at physics.mcmaster.ca (Christine Wilson) Date: Wed, 13 Nov 2002 12:15:44 -0500 (EST) Subject: [asac]science examples for calibration review In-Reply-To: <15815.64382.637873.458379@polaris.cv.nrao.edu> Message-ID: Hi, everyone, As we discussed in our telecon last week, one of the first tasks of the calibration group is to review the calibration requirements for ALMA (see text of draft Level 2 milestone below). This review is to include science examples and this is an area where the ASAC can provide useful input to the process. I ask you all to try to come up with one example of science that will be done by ALMA. For examples of the types of things, you can have a look at the science examples in the stringency report from our last face-to-face meeting. Stephane will circulate a summary of the key calibration issues by email in the next day or so. If you can design a science example to exercise one of these specific issues (i.e. 1% calibration accuracy, total power stability, etc.), that would be excellent. But even if your favorite science example doesn't seem particularly difficult for ALMA to achieve, please pass it on, as I think having a good range of science examples will be important for this exercise. Please send your contributions to John Richer and me by Monday, December 2. Thanks, Chris Level 2 milestone: Review of calibration requirements with science examples complete. This includes: phase, amplitude, bandpass, polarization, antenna location, illumination offset, pointing, focus, delay, opacity, and decorrelation correction. How and where and at what frequency opacity is required to be measured at the site. From soliver at nrao.edu Mon Nov 18 13:16:53 2002 From: soliver at nrao.edu (Stacy Oliver) Date: Mon, 18 Nov 2002 11:16:53 -0700 Subject: [asac][almanews] ALMA Memos 441 and 423 Released; Revision of ALMA Memo 438 Released Message-ID: ALMA Memo #441 Enhancing the Performance of the Baseline ALMA Correlator Ray Escoffier and John Webber (NRAO) 2002/11/11 Keywords: correlator, digital filter The performance of the baseline ALMA correlator in spectral resolution can be easily and inexpensively enhanced. The time-division architecture of the system is completely consistent with the requirements of a so-called digital hybrid correlator. By replacing the present digital filter card with one of a more complex design, the spectral resolution performance of the system could be increased by factors as high as 32. View a pdf version of ALMA Memo #441. http://www.alma.nrao.edu/memos/html-memos/alma441/memo441.pdf Download a postscript version of ALMA Memo #441. http://www.alma.nrao.edu/memos/html-memos/alma441/memo441.ps ________________________________________________________________________________________________ ALMA MEMO #423 The Vane Calibration System Revisited S.Guilloteau (IRAM / ESO) 2002/05/27 I re-investigate the semi-transparent vane calibration scheme proposed for ALMA, taking into account expected saturation behavior of the receivers. This memo improves on memo 371 by using more accurate derivations and better estimates of the receiver saturation temperatures. It is shown that to reach a given precision in calibration, the saturation on the vane must be less than this precision. Suitable values for the vane transparencies are given. The vane transmission can be calibrated in a few minutes (at mm wavelengths) to 1 hour (above 275 GHz) by measurement of an astronomical source (nearby quasar). A derivation of the saturation temperature from a measurement on the vane and on an ambient load is presented. The case of partial saturation on the vane is explored. Using the derived saturation temperature in this case requires a more accurate measurement of the vane transmission, but is the only way to reach the specified accuracy. Given the simplicity of the vane system (passive, slow device, in the receiver cabin), compared with the complexity, speed and location of the dual-load system, I recommend that ALMA develops and adopts such a scheme for the receiver calibration. View a pdf version of ALMA Memo #423. http://www.alma.nrao.edu/memos/html-memos/alma423/memo423.pdf Download a postscript version of ALMA Memo #423. http://www.alma.nrao.edu/memos/html-memos/alma423/memo423.ps ________________________________________________________________________________________________ ALMA MEMO #438 Measurements of Materials for SIS Mixer Magnetic Circuits G. A. Ediss and K. Crady National Radio Astronomy Observatory Revised 2002/11/14 Original 2002/11/01 Keywords: magnetic materials, hysteresis measurements Measurements have been made of various magnetic materials in order to improve the flux density at the SIS junction positions in the mixer. The materials measured are Hiperco 50A, HyMu 80, Consumet iron and Magnet iron. Magnet iron is recommended for unannealed use. Consumet is recommended for annealed use. Hiperco 50A can be used annealed if large hysteresis can be accepted. For highest flux density for lowest drive current, annealed Consumet should be used. ALMA Memo 438 has been revised as of November 14, 2002. The new version is numbered as ALMA Memo 438.1. To view or downloaded the revised version ( November 14, 2002), please use the following links: View a pdf version of ALMA Memo #438.1. http://www.alma.nrao.edu/memos/html-memos/alma438/memo438-1.pdf Download a postscript version of ALMA Memo #438.1. http://www.alma.nrao.edu/memos/html-memos/alma438/memo438-1.ps _______________________________________________ Almanews mailing list Almanews at listmgr.cv.nrao.edu http://listmgr.cv.nrao.edu/mailman/listinfo/almanews From awootten at nrao.edu Fri Nov 22 17:34:35 2002 From: awootten at nrao.edu (Al Wootten) Date: Fri, 22 Nov 2002 17:34:35 -0500 Subject: [asac]ASAC Report Message-ID: <15838.45307.877585.25839@polaris.cv.nrao.edu> The ASAC Report, from their September face-to-face meeting, was presented to the group previously known as the ACC on 2002 October 30-31. The report may be obtained from http://www.cv.nrao.edu/~awootten/mmaimcal/asac/ASACSocorroReportFinal/ASACSocorroReportFinal.ps It will be posted to the usual location on the ALMA Web Pages in due course. In the Appendix to the above report on Site and Stringency there are a number of voluminous figures; a version of the report without this Appendix is also available at: http://www.cv.nrao.edu/~awootten/mmaimcal/asac/ASACSocorroReportFinal/ASACSocorroReportonlyFinal.ps and the Appendices are independently obtainable at: http://www.cv.nrao.edu/~awootten/mmaimcal/asac/ASACSocorroReportFinal/ASACSocorroReportappendices.ps Acrobat pdf versions are available at the same locations, with a file name ending in .pdf. 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 wilson at physics.mcmaster.ca Thu Nov 28 19:22:17 2002 From: wilson at physics.mcmaster.ca (Christine Wilson) Date: Thu, 28 Nov 2002 19:22:17 -0500 (EST) Subject: [asac]reminder: science examples for calibration review Message-ID: Hi, everyone, Just a reminder that the calibration group needs examples of ALMA Science as part of meeting one of their first milestones (see my original email below). I've also attached the email from Stephane discussing the particular aspects of calibration that could use examples, but I'm sure ANY science examples that illustrate calibration requirements would be very welcome. Please try to take some time before our telecon next Wednesday to try to come up with a specific science example that could be useful to the calibration group. This is one area where having input from as diverse a group of science interests as possible is very important. Please send your examples to me and to John Richer Thanks, Chris ---------- Forwarded message ---------- Date: Wed, 13 Nov 2002 12:15:44 -0500 (EST) From: Christine Wilson To: asac at polaris.cv.nrao.edu Subject: [asac]science examples for calibration review Hi, everyone, As we discussed in our telecon last week, one of the first tasks of the calibration group is to review the calibration requirements for ALMA (see text of draft Level 2 milestone below). This review is to include science examples and this is an area where the ASAC can provide useful input to the process. I ask you all to try to come up with one example of science that will be done by ALMA. For examples of the types of things, you can have a look at the science examples in the stringency report from our last face-to-face meeting. Stephane will circulate a summary of the key calibration issues by email in the next day or so. If you can design a science example to exercise one of these specific issues (i.e. 1% calibration accuracy, total power stability, etc.), that would be excellent. But even if your favorite science example doesn't seem particularly difficult for ALMA to achieve, please pass it on, as I think having a good range of science examples will be important for this exercise. Please send your contributions to John Richer and me by Monday, December 2. Thanks, Chris Level 2 milestone: Review of calibration requirements with science examples complete. This includes: phase, amplitude, bandpass, polarization, antenna location, illumination offset, pointing, focus, delay, opacity, and decorrelation correction. How and where and at what frequency opacity is required to be measured at the site. _______________________________________________ Asac mailing list Asac at listmgr.cv.nrao.edu http://listmgr.cv.nrao.edu/mailman/listinfo/asac -------------- next part -------------- The ALMA project is currently encountering some difficulties in developping and realizing devices to be used for the calibration of the various instrumental parameters. Among the possible devices which have not been sufficiently developped is an accurate coherent source (made of a phase-locked photonic emitter located in the subreflector) which, if sufficiently accurate (in amplitude, phase and polarisation as function time and frequency) could have been used to calibrate the instrumental parameters. Current projections from the engineers quote amplitude variations as function of frequency of several 10 %, unclear polarisation properties, and significant difficulties to achieve high amplitude stability versus time. In our present understanding, it is unlikely that such a device can be used successfully to achive high accuracy calibration of either the bandpass or the polarisation. To help investigating the problem, it is important to re-examine what are the REAL specifications for the calibration of ALMA, and to put also in perspective what would be goals to be achieved if possible. Specifications are the performance ALMA should deliver in all (average) circumstances. In terms of instrumentation, instrumentation out of specification should be refused. Thus, we cannot impose unachievable specifications. On the other hand, "Goals" indicate what level of performance might be reached on special circumstances, involving either dedicated observing modes, or fortunate coincidences (such as exceptionally good weather, or strong astronomical calibration source available). The "old" ALMA project Book mentionned the following for Calibration Table 3.1 ALMA Calibration Requirements. Pointing 0.6" absolute Primary Beam 2-3% Baseline Determination 0.1 mm Flux Calibration 1% absolute flux accuracy goal Phase Calibration 0.15 radian at 230 GHz Bandpass Calibration 10000:1 to 100000:1 Polarization Calibration 10000:1 Single Antenna Calibration Employed This is a mixture of Scientific specifications (e.g. 0.15 radian at 230 GHz), goals (e.g. 1%), Engineering specifications (e.g. 0.6") and "out of the blue" numbers (e.g. Bandpass Calibration 100 000:1) We now have to set Engineering specifications on some key items in ALMA. For example, the receiver stability has to be specified. It can be derived from several of the above numbers. Single-Dish observations require short term (1 second) stability of order 10^-4, but this number is Frequency dependent. 1 % amplitude calibration accuracy requires the receivers to be significantly more stable than 1 % (say 0.1-0.2 %) but on timescales much longer (say 10 minutes). The most difficult issues to be translated in Engineering specifications are the Bandpass and the Polarisation Calibration. To help us in doing so, we would like to re-assess the actual astronomer needs. To do so, we ask you to send us a few Science Examples (2 or 3 would be sufficient) which would represent - a "normal" experiment, which would be used to derive ALMA Specifications - a "demanding" experiment, which would be used to derive ALMA Goals focussed on Bandpass and Polarisation issues. The Science Example should be short (1 to 2 lines of description will in general be sufficient). It should contain the expected observing frequency, the typical linewidth, and the expected signal intensity (in Flux density, Brightness or Line-to-continuum ratio). For Polarisation, the expected percentage of polarisation and requested precision on the position angle of linear polarisation should be mentionned. Also, it may turn out to be difficult to equip ALMA with adequate devices (most likely quarter wave plates) for polarisation measurements at all frequencies. Your help is requested to define which frequency(ies) is(are) the most important. ----------------------------------------------------------------------------------------- Here is an example (for Bandpass). - "normal" experiment: Detection of narrow absorption lines in front of a quasar. Observing Frequency: any from 90 GHz to 700 GHz Linewidth: 1 km/s Line-to-continuum ratio: 0.01 Implications on Bandpass accuracy 1000:1 on a 1 to 3 MHz window - "demanding" experiment: Observation of a narrow absorption lines in front of a quasar to measure accurate isotopic rations. Observing Frequency: 300 GHz Linewidth: 1 km/s Line-to-continuum ratio: 0.01 Implications on Bandpass accuracy 10000:1 on a 3 MHz window (to get a few % accuracy on the line intensity) - "demanding" experiment: Detection of a broad, weak emission line from CO around a bright quasar Linewidth: 600 km/s Line-to-continuum ratio: 0.01 Implications on Bandpass accuracy 1000:1 on a 600 MHz scale