Australia Telescope Compact Array report

Staff

It has been a busy time farewelling old and welcoming new staff members. After being with the ATNF for four years, Scott Cunningham and Vivian Wheaton have left to spend time travelling and exploring new opportunities. Martin Oestreich, who has spent nine years in the ATNF electronics groups in Marsfield and Narrabri, has left to take on a new role at the AAT at Siding Springs. Alison Ryan has finished up after completing her apprenticeship at the ATCA in January. Right up to her final hours, Alison was down in the cable pits and ditches working hard to finish her fibre optic work. After 16 years with the ATNF, Trina Gordon has left to take on other work in the Narrabri region. We wish Trina the best with her new path. Jacqui Wieringa has gone on maternity leave until 2003.

Fresh from the South Pole, we welcome back Ben Reddall, who has taken over Martin Oestreich's role as Electronics Group Leader. While Jacqui Wieringa is on leave, we are pleased to have Judy Stump keeping the library up to its usual standard. We also welcome Debbie Rowe-McDonald and Eric Darcey. Debbie has joined us as a cleaner and Lodge assistant, while Eric will work on the antenna drives and other power control systems.

We currently have three vacancies in the electronics group, which we expect to fill imminently. A systems scientist position is also currently being advertised.

Operations

Array usage

Figure 1 gives the usage of the compact array for the 2002 January term.

The weather was kind to us this term. The Antenna Control Computers remain our main source of equipment failure. Also during the term, one antenna was down for three days with problems in the drive electronics.

Figure 1: ATCA 2002JANT usage

Millimetre observing

Millimetre observing during January (summer!) term was restricted to four 12-mm proposals (one of which experienced rain) and various tests. More serious millimetre observing began in late May, with 3-mm observations of the Galactic Centre. There has been a healthy request for millimetre observing during May term, with 78% and 22% of time scheduled to centimetre (3-20cm) and millimetre (3, 12 mm) observing proposals, respectively. The arrays scheduled during the May term consist of 6A, EW352, EW214, 1.5B, 750B, H75 and 6C. This is the first time that EW214 and H75 will been scheduled, and the first astronomical use of the north spur. As mentioned in the previous newsletter, we will be trialing a form of flexible scheduling in May term which allows millimetre observers to swap their allocated slot with a partnering centimetre observer. This trial will continue into mid-October, when we will revert back to standard fixed scheduling for the summer months.

Observers questionnaires

The observers questionnaire is now on-line. All ATCA users are encouraged to complete this. To help keep statistics on the extra requirements at millimetre wavelengths, there is an additional millimetre questionnaire. Users of the millimetre systems are strongly encouraged to complete an on-line questionnaire. The questionnaires are linked from

http://www.narrabri.atnf.csiro.au/feedback

Building work

We are about to start a parcel of work on the buildings at the ATCA. This will include revamping the reception area in the Control Building, refitting the men's bathroom at the Lodge, and extending the Receiver Lab building to make space for the new staff arrivals. There are numerous other smaller jobs. We will attempt to minimise any disruptions to observing and Lodge perations.

ATCA upgrade

Antenna control computers

We reached a milestone in March 2002, when interferometric fringes were produced when controlling the antennas with the new antenna control computers (ACCs). Work on debugging and integrating them with the on-line system continues. We plan to use the new ACCs for astronomical observations in mid-July, and aim to switch across to using the new ACCs permanently in early August.

Antenna structure

A photogrammetric survey of antenna 2 has proven to be a treasure trove of information. Unlike holography from a geostationary satellite, the photogrammetry can be done with the antennas at any elevation. It also decouples the deformation of the main subreflector from flexing of the quadrapod structure and lateral and rotational sags of the subreflector. The main purpose of the survey is to understand beamshapes and changes in antenna efficiency at 3-mm wavelength, as a function of elevation. An important question is whether enhanced control of the subreflector can allow us to compensate for the various distortions, and so improve beamshape and regain some lost efficiency.

Receivers

Recently, a mechanism to measure the system temperature (by periodically flipping a room temperature paddle in front of the 3-mm horn) has been implemented in the on-line system. This provides a nominal above-atmosphere value of the system temperature for calibration purposes.

Signal distribution

Good, steady, progress continues with the new signal distribution system. Fibre connections have been completed to all station posts, and the fibre patch panel in the screened room is finished. Ethernet connections are now available to all antennas. The array now runs completely on the new fibre-based local oscillator (LO) distribution system. With the exception of antenna 3, the IF returns on all antennas are now on the new single-mode fibre. Work on antenna 3 will be completed in the near future. The new LO system uses two LO signals to each antenna - one at 160 MHz and another in the 13 GHz range. Integrating the 13 GHz round trip phase measurement system into the on-line software needs to be completed.

Mopra

During January term, usage at Mopra was restricted to LBA and VSOP observations. During the May term, millimetre observations at Mopra will be jointly run by the ATNF and UNSW, with each allocated six weeks of observing time. Lucyna Kedziora-Chudczer (for UNSW) will act as a "friend of the telescope" during the observing period. Additionally AAO has agreed to provide some engineering support at Mopra during the term. These arrangements should provide good support and more timely attention to any system problems. The ATNF-supported observations have been allocated through the normal time assignment process. Mopra will also continue to be used for LBA and some VSOP observations during the June term.

Bob Sault
Officer-in-Charge, Narrabri
(Bob.Sault@csiro.au)