Report to the JCMT Board; April 2007
(for the 6 month period ending 31 January 2007)

Summary

• The JCMT was closed from Feb-Jul 2006 for heavy engineering.
• By the end of August the inclinometry and pointing had been recovered and pointing quality remained satisfactory through September.
• The 6.8mag earthquake of 15 October had little apparent effect, although it took about 2 weeks to determine that. The quality of pointing on Oct 23 was still essentially nominal . . .
• . . . However, the first full pointing run afterwards indicated a deterioration in the pointing performance, especially in azimuth.
• Commissioning of HARP in November was plagued by separate pointing problems related to the (mis-)alignment of the K-mirror (field corrector). This only served to confuse the effort to understand and improve the basic pointing as described by and with the use of RxA, and is still an unresolved issue.
• Vibrations in the SMU have been reported since Fall 2006 and various adjustments have been made to the Crown Amp gain settings to alleviate the problem. The impact of these vibrations upon the quality of pointing has not been established, but was suspected throughout the period. The vibrations are now mainly under control but do still occur irregularly and occasionally at low amplitude.
• In February, a change in the pointing data acquisition technique - from jiggled maps to FIVEPOINTs (still including SMU chopping) - finally resolved the RxA pointing problems and nominal performance (1.5"-2.0" rms in each coordinate) was restored.
• Transit step and central bearing race defect measures have not yet resumed, but would not appear to be the limiting constraint on pointing.
• Temperature corrections will resume shortly : a new logfile containing engarchive temperature measures and antenna- and SMU- positional data has only recently been inaugurated. Approximately a month's worth of data are needed to provide statistical confidence in any changes to the current algorithms - which appear to be working satisfactorily in any case.