SD-forum #3 --- minutes
12 august 1996
Only one item dealt with : the Focus Cabin Translator.
- Both the Hardware and Software have now matured, and reliable operation should be the norm. However, problems doubtless remain, and these need to be addressed. No additional problems were reported at this meeting; the observer logs do currently contain obscure references to "problems" - but unless the problems are described in some detail to an FCC expert (M.Kesteven; B.Preisig or P.Payne), they will remain unresolved.
- The translator in active tracking mode can improve significantly the telescope's performance at frequencies above 8 GHz. The use of TRKFCC is thus strongly encouraged.
- Are there user problems? Does it need further work to make it useable? friendly? The difficulties reported seem largely to have their origin in unfamiliarity with the system. A user guide is available in the Blue Binder in the control room. The guide is also available on the web, (FCC) in the on-line library.
URL: http://www.parkes.atnf.csiro.au/library/MANUALS/FCC/FCC_toc.html
The linkage between the control system and TRKFCC was also seen as a problem - this will be addressed (see below).
- Operational implications ?
1. TRKFCC needs to know how the antenna deforms with elevation. This is a calibration exercise. An upgraded SPOT is required.
2. It appears that there is an axial offset which varies - possibly with temperature (night/day). The observer needs a utility that will establish the offset easily.
Items 1 and 2 point to the need for an enhanced SPOT - able to perform a series of orthogonal scans to determine the location of the best fit focus (the calibration operation), or to determine the focus offset (the observer's adjustment at the start of an observation). MJK will send a suggested specification to E.Troup for comment.
3. The antenna's pointing model varies with frequency; and there are additional changes to the model if the focus tracking is invoked. This means that TRKFCC and the control system need to communicate - a change in frequency (eg, 1.4 GHz to 8 GHz) means that the TRKFCC focus function will change, and therefore, so will the pointing model. Communication is also required whenever the tracking mode changes (ie, from TRACK to LOCKED). MJK and ET will look to upgrading TRKFCC so that it can revise the pointing parameters - the "allocate" problem needs to be addressed.
4. It would be useful if DESKWATCH and SHOWTEL could be expanded to show the current FCC status. The data cannot easily be placed in DESKCOM (the shared common area) since this gets over-written by the DESK machinery. However, additional shared memory could be allocated, and DESKWATCH and SHOWTEL could be modified appropriately - E.Troup to advise.
5. A responsible control system should provide some measure of archiving of its operations. TRKFCC maintains a log of the FCC position, and all operator requests. (At present there is no global archiving of the antenna status and position on a regular basis, although this matter has been discussed in the past. A.Wright will look to providing MJK with the reports of those deliberations.)
One possibility is to provide a one-sec logger of the antenna status and position (desirable for the multi-beam project), and to include the FCC data, provided by TRKFCC. (MJK).
- Implications for the observer.
1. RFI ? There is very clear evidence of RFI if the cabinet doors are open. It seems that the power cabinet is even noisier than the computer cabinet. A. Wright will look to obtaining 1.4 GHz spectra with the doors open - this will provide a "worst case" inventory, and provide a guide to spectral features to which the observer should be alert. A long integration with the doors closed will be done by L.Stavely-Smith and R.Haynes in October. The RF sealing of the cabinet (the "fingers" around the periphery of the door) are fragile, and were damaged on delivery. Now that the system has stabilised, and the need to open the doors is much reduced, it might be worthwhile renewing the fingers.
The "quiet mode", with the motors disabled, should be looked at, but it is unlikely to help - the power amplifiers themselves remain active.
The ultimate "quiet mode", with both cabinets powered down should also be checked - it may be the only recourse for some sensitive observations.
2. Polarisation : you cannot rotate the receiver as used to be the case. (Very few receivers are mounted at a platform centre).
3. Spectral line baselines - do you keep the receiver at the best-fit focus at all elevations, or do you keep it fixed and allow the best fit focus to drift by?
- Are there user problems? Does it need further work to make it useable? friendly? The difficulties reported seem largely to have their origin in unfamiliarity with the system. A user guide is available in the Blue Binder in the control room. The guide is also available on the web, (FCC) in the on-line library.
next meeting : Tuesday, September 17; at 11:00 am.
ATHELP is a new web page designed to assist observers with on- and off-line problems. [URL : http://www.atnf.csiro.au/observers/athelp.html]