Notes from Commissioning Coordination Meeting 8 November 2002 1. GBT Commissioning Review on Tuesday, November 12 The GBT Commissioning and Development Review will be held on November 12 in the Jansky Lab Auditorium. All Green Bank staff are invited to attend. Several staff members from other NRAO sites will be visiting, and others will be attending via video connections. Anyone working in technical or scientific areas in support of the GBT ought to attend, and all others who would like to know more about what is happening on the GBT are encouraged to attend. Primary objectives of the review are o Description of status and plans for commissioning and operations o Description of development plans and realistic schedules o Discussion of management process and areas where there are challenges o Discussion of ways to involve more NRAO staff to support the efforts productively o Opportunity for general comments and suggestions by participants A dry run of presentations will begin at 9am on Monday in the Conference Room. 2. Azimuth Track Review Panel Phil gave a summary of the preliminary outcome of the GBT azimuth track review that was held last week. The panel is still at work on their final report, which is due by 15 November. The panel was a high-level group of engineers and scientists from universities, consulting firms, and other institutes. They worked well as a team, and considered the issues very carefully. _Preliminary_ recommendations were o Perform a strength analysis of the flex plates with a field study to verify o Continue to monitor tilts and shim when the limit from the above analysis is reached o Develop and implement a joint stiffening and bridging base plate with a possible wear plate retrofit o Install a bridging wear plate over one, strengthened splice o Measure and monitor wheel profiles o Develop criteria and concepts for a new track o Measure the hardness of the wheel and wear plates and determine the source of the metal flakes seen on the track This week, we have had a new development with the track. A careful inspection of track bolts has found 10 broken bolts. Most of the broken bolts were in the holes nearest the splice, but several were at mid-span. We have documented the details of the inspection and broken bolts and forwarded this information to the panel. They are considering this development for inclusion in the report. 3. Commissioning and Program Checkout Status Three more wide-band Spectrometer modes were checked out during the week by Dave Hogg and Frank Ghigo (two 800 MHz modes [single bank] and one 200 MHz mode). The data have not been fully analyzed yet. Preliminary examination did not indicate any obvious problems other than some baseline wiggles, which are probably not associated with the Spectrometer. Multi-bank capability was released with the recent M&C release, so commissioners can begin checking out these modes. Multi-bank capability is not fully supported by AIPS++ yet, but you reduce the data by filling each bank separately using the d.open() command. Many observing programs are awaiting multi-beam and multi-bank capabilities, so this activity is a priority. Attempts to do some pointing runs were winded out this week. Given that we have lost a couple of nights recently to high winds, Rick asked if we had any good statistics on wind speed that would provide some guidance to observers. Toney stated that he could analyze the data from the Tracking Station weather files without too much difficulty. The K-band receiver will be installed early next week, and commissioning work will begin in the days following the review meeting. Ron stated that he had received a few comments on his multi-IF specification memo. There is still time to get comments in before any decisions or implementation work begins (in a couple of weeks). 4. Software status Nicole distributed a status report. An interim M&C update, 3.8.1, was released on Thursday, 7 November. Release notes were distributed by email. The next M&C release (v3.9) will be on 11 December. Requests for items to be included in the January release should be received no later than 9 December. Work on v3.9 is underway and is going well. Tasks underway include Spectrometer root cause analysis, multi-bank capability, PF2 manager, antenna control improvements, and Q-band receiver manager work. 5. Spectrometer status Rich was in a safety training class on Friday, and sent the following report by email: What got done this week: 1) Timing measurements for spigot card developement. They did not come out the way Ray expected them to and additional work is needed here. 2) Tested new PALs which are supposed to help with glitches in the ACF. They seem to basically work. Have not seen any large glitches since they were installed. However, we have seen smaller glitches. The cause of these has not been found. 3) More tests to uncover the causes of problems with LO Blanking. Have found that the integration count appears to be incorrect. This is a bit of headway. Now we need to understand why the count is incorrect. Next week: - Ray will be here on Wednesday for further work on the spigot card. - Really need to allocate two days to replace the paddle boards. I looked at some of Roger's data on the K-band receiver and one receiver produced an ACF that was apparently corrupted by a bad connection on a paddle board. (Saw a sine wave with a period of 16 lags.) - Need to have a close look at raw data for additional clues about the LO Blanking problem. 6. Baseline Investigations Roger sent the following report: * The system seems to have good days and bad days. On good days, the baselines I've seen with the Kband receiver in the lab typically have RMS over 750MHz of 1.2 to 1.5 times theoretical for 5min On and 5min Off scans. On bad days, the RMS is 3-5 times (or more) worse. We have made attempts to determine what causes the bad days, but it is slow and tedious work, and so far have not nailed it. * The Xband front-end shows TP cycling of 2-3% with ~3 minute periods. I suspect this is due to defective cryo LNA's coupling cryogenic temperature cycling to gain, although that suspicion is not totally proven. This cycling I believe limits the baseline quality at Xband. * The 2.4 MHz optical IF modulator ripple does bleed through into the Tant difference plots, sometimes worse than others. This effect limits the RMS we can achieve, and so limits the sensitivity. * A spike (usually at 100MHz) is often seen in spectrometer data. Rich believes this is a result of the "paddleboard" problem. His fix for that should be scheduled and accomplished as soon as possible. A couple of other opinions: A lot of wasted observing time could be saved if we had convenient Total Power monitors readily available. It would greatly help isolate problems if the DCR could be run in parallel with the spectrometer. Rick added a few more points. There will be an effort to see if the direct laser modulator eliminates the 2.4 MHz ripple. It has no servoed gain feedback. Ron noted that this may have some adverse consequences to other types of observing. The new optical modulator that the vendor claims may reduce the 2.4 MHz ripple has not been received yet. A 10 MHz ripple popped up on the X-band system for a while. There is no idea where this came from. 7. RFI Mitigation status Rick reported that the IPG has been heavily occupied with tests and specifications for the shielded rooms and appliances in the new visitor center. Work on the shielded rooms in the Jansky Lab is awaiting parts. John reported on the work on the feedarm servo system. There are a few more cable connectors still to go. When this is finished, an overnight shutdown is needed to disassemble the cables, modify the bulkhead box, and reassemble it all. This is a 2-day job, even with extra hours worked. 8. AIPS++ News Joe McMullin reported that the group was preparing for the GBT review and for the AIPS++ review to be held in January. Joe and Steve Myers will be arriving on Monday morning. The group has been working with Jay Lockman this past week on a new imaging tool that allows a sky overlay of sampling positions. Work is also underway on defect resolution and multi-beam, multi-IF implementation. Some of this work is described in the minutes of the AIPS++/Single Dish meeting. Given the recent changes in AIPS++ management and other pressing activities, work on performance enhancements is on hold for a while. PRJ // 9 November 2002