Calibration Group Phone Telecon Meeting Minutes - 2003Mar12 Attending: Bacmann, Butler, Carter, Guilloteau, Hills, Holdaway, Kohno, Mangum, Pintado, Radford, Saito, Wootten (apologies to anybody I missed - there were a few connects/disconnects during the telecon). Agenda: - amplitude cal devices, and near-term decisions to be made. - milestones - other? Minutes: - Stephane went over the note that he sent just before the meeting ( click here for it ), and discussion followed. Butler pointed out that the thing to do, probably, is to pursue (from the "Possible decision paths" part of Stephane's writeup) point (1) at the ASAC meeting in Grenoble on April 2-3, ask the FE IPT for (2a) and/or (2b), and follow (3a) - i.e., abandon the dual-load in the subreflector. Wootten agreed, pointing out that "delta development" on the dual-load was small, and didn't warrant continued support of that system. Mangum agreed, but pointed out that the cost savings from (3a) would not necessarily allow for (2a) and/or (2b), since if we are left with only the S/T vane, then the contingency goes up for that system, because of the risk involved. Hills pointed out that we should still pursue a partially reflecting (polythene or teflon?) vane, at 45 deg angle to the feed, directing the beam off into a load. Polarization may be a problem with this system though. Carter pointed out that with the current system, the LO is reflected back through the feed, and the 45 deg. reflecting vane would not suffer from this problem. Hills reminded everybody of the vane temperature and scattering problems with the S/T vane. Carter noted that the scattering had been measured, and was "not a problem", but would not hold to a specifically small number (1%) when pressed by Hills. Butler pointed out that with the reflecting vane you need to fill the beam, and this might be difficult given space constraints in the Rx cabin. Carter agreed. - Jesus-Martin Pintado presented a summary of the semi-transparent vane tests to date. Click here for a short writeup of the tests. They have had a few hours of test time on the 30-m telescope. Because of time constraints, the test that they did was conducted with the S/T vane pretty close to the Rx. Absorption by the vane was measured by looking at cold and ambient loads. Several measurements were made for each frequency, and averaged. The scatter between the measurements on different days is up to 10%. Tilting of the vane up to 5 deg was possible. They did not measure Tvane or true vane losses. Kohno asked if the measurements were stable when looking simply at the ambient or cold load - Pintado answered that they were. The future test plan is to try to move the vane further from the feed, to make real astronomical observations and compare with the current calibration devices on the telescope, and to test some new materials sent to them by Carter. These tests will not occur until late April/early May, however, and so will not happen fast enough to help in the decisions discussed above. - Discussion turned to milestones. Butler has to get moving on trying to meet II.A. He will attempt to get this done while in Tucson next week. Other milestones are related to the document due end of June. Hills was asked about II.B.2 (the "auxiliary" calibration devices, or what is sometimes called the "weather station"). He has worked on it, but not much, given other time constraints. He will work on it next week. He solicited input from other members of the cal group on what kinds of devices might be desired or needed. Butler pointed out that the intent was to have the ATM software available to attempt to see really what we needed, but that will not happen. Pintado noted that Pardo is now working full-time on trying to get a working ATM library available for delivery, and this should occur in early April. Thus the document produced for II.B.2 will not contain this analysis, which will have to come at a later date. - Final discussion concerned the issue of polarization calibration. It is now clear (and imminent) that Myers will be leaving the ALMA project to go full-time on AIPS++. This, as has been known for some time, will leave a void in the polarization calibration area. We need to fill that void, but it is unclear how. People in the cal group were encouraged to think about possible people to work on this problem (either already in the science IPT or not). dutifully scribed by bjb, with input from sg. 2003Mar12.