Notes from Commissioning Coordination Meeting 11 October 2002 Richard summarized the investigations into the feedarm motion as a function of elevation angle. The linear structure model of the antenna predicts that the feedarm should follow a smooth curve in both the up-down (y) and the side-to-side (x) direction as the arm tips over in elevation angle. Quadrant detector data show instead that the arm follows an S-shaped curve with inflections around 40 and 60 degrees elevation. Residuals from the linear prediction are a few mm in both the x and y directions. There also is an apparent hysterisis loop in both x and y that is seen in the quadrant detector data and ground-based survey data to a target on the tip of the feedarm. The excursions in the feedarm position are at least qualitatively similar to the on-sky pointing residuals seen during the summer. Measurement of the resonant frequencies of the structure with accelerometers show that the ~0.77 Hz mode takes a step down to ~0.74 Hz between 65 and 70 degrees elevation. Thus, there are several pieces of independent information that indicate feedarm motions that we were not predicting. We have decided that it would be prudent to suspend observations until at least Tuesday so these data can be reviewed by the Observatory engineering staff. 2. Observing Program Checkout & Commissioning News Richard reported that we have checked out most of the programs that we can, given the present suite of capabilities. Frank has been working on Spectrometer checkout and has placed a table of the priority modes on a web page in the 'gbt/gbtstatus/checkouts' area. Links to reports on the mode checkouts are included. Several modes have been successfully checked, but there are also several modes remaining to be done. Ron went through the K-band commissioning plan. He expects to have it finished the first of next week. It would appear that most capabilities at K-band would be finished by the end of the year, although some work will extend beyond that. The plan will be structured to put observing programs on the air as soon as the relevant capabilities are available. Further details of this plan will be recorded in next week's report. Roger reported that he had taken 6-7 hours of data with the K-band receiver connected to the Spectrometer in the Equipment Room. These data are not fully analyzed, but it does appear that 1 of the 8 Rx channels has a gain instability that will require work in the lab. When the K-band receiver was in use in March and April, scans occasionally showed some ringing. This may have been seen in the lab tests, which may help to narrow down the cause. Dana has continued to work on X-band baselines. Observations in the 800 MHz bandwidth mode going on and off a strong continuum source show significant structure on different scales. Preliminary indications are that this structure is originating in the receiver, somewhere between the feedhorn and first LO. 3. Spectrometer News Rich reported that Ray Escoffier had been out again last week to work on the spigot card. Ray sent a report that most of the 1024 and 2048 lag modes had been successfully tested. A few modes did not work and the 512 and 256 lag modes had some problems. An lab observation with an artificial pulsar was taken and the data sent to David Kaplan for analysis. There are several things left to check out, and Ray is planning another trip back to GB at the end of this month to continue work. Rich reported that a problem in the memory board (LTA) was fixed this past week. The paddle board problems are getting worse; hardly a day goes by now without a problem. The new connectors are due in about a week. Rich will organize a production line to replace these as soon as possible. The replacement work will take about a day. The problem with single lag blips in the autocorrelation function have been narrowed down to a 1 bit shift to the left. The new Spectrometer engineer, Holly Chen, will start work on Tuesday. Rich will begin training her on Spectrometer support right away, which should help with staffing for both this and other projects. 4. Software News Nicole reported that work on the October M&C release (v3.8) was on schedule. The focus continues to be on the Multibeam/Multibank capability. Amy has completed the Spectrometer simulator that will serve as an aid in developing and testing this capability. A "Community Meeting" was held on Thursday, 10 October to discuss the user interface Configurator. 15 issues were identified; 14 are easily addressable and 2-3 of these were already done on Friday. Work on a mockup for the Status Panel is also underway. The full Software Development Division report is available at http://tryllium.gb.nrao.edu/ 5. AIPS++ News Joe McMullin reported that a new data compression algorithm has been installed in the Filler. This should get around the quantization problem reported earlier while still providing about a factor of 2 compression. Some investigations into the speed of various parts of the Filler indicate that the Van Vleck correction is responsible for much of the total time required to fill a scan. There appears to be some optimization possible on that routine, and the way in which the corrections are made as the data are coming in might also be changed to speed up filling at the end of a scan. This matter is still under study. On the Dish side, it appears that the "d.getscan" command is taking longer than expected to execute. Since this command is used over and over within Dish, optimization could make a big difference in overall speed of the package. Work on a number of other areas is proceeding, including total power calibration. Targets recently completed include assembling scans for the Dish performance assay Total Power On-the-fly mapping capability Imaging functions Data for the e2e project 6. Other Business Phil reported that Karen O'Neil has accepted an offer for the Assistant Scientist opening, and will begin work in January. Karen is presently a staff scientist at Arecibo, and is very experienced in AIPS++ issues, spectrometer support, documentation, and general observer support. She should be a strong and welcome asset to the GBT team. 7. Actions No new actions were added this week. PRJ // 14 October 2002