Report to the JCMT Board - March 2004

Inclinometry
Measurements of the antenna track profile are made every week or so, and have shown no substantial changes during the past 6 months. The use of hybrid (ClockWise & CounterCW) track models equalizes pointing quality in the north and south.

All-sky pointing
All-sky pointing has remained good throughout the period, in terms of both collimations and rms scatters. Values for the latter are 1.5" or better in each coordinate during stable parts of the night. Pointing model updates have been necessary only 3 times in the period : twice in December following repairs to the SMU and a central bearing load adjustment (CBLA), and once in March after a SMU-repair/CBLA combination. No faults were filed concerning poor pointing during the period, and from dozens of observer's reports on their experiences at JCMT during the period pointing is mentioned only once : in that it "caused no problems". That's the way - a-huh a-huh - I like it !

Transit step & transit tracking
Transit tracking still exhibits abrupt steps at transit that remain something of a mystery, with differences in behaviour at different elevations that cannot be explained by our previous concepts of hysteresis or friction in the bearings. The size of the problem, though, is small (~1 arcsecond steps), and tracking through transit remains good at levels of 1" rms per hour in each coordinate. We can probably tolerate this level of performance; continued investigation of the problem requires substantial amounts of (grade 3) time.

Focus
The December and February repairs to the SMU necessitated a series of minor zero-point corrections (the latter incomplete at time of writing). Focusses are maintained to within 0.1mm rms in Z and 0.2mm in X & Y.

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