Other news from the PdBI

Weather conditions and observations

The interferometer recorded a very high observing efficiency during the months of January: 50%, more than twice the efficiency of last year, with excellent prerequisites for 1.3mm observations with high phase stability, and with the sixth antenna almost fully operational since the begin of January.

As far as A-rated projects are concerned, we look forward to bring these to completion in the current winter semester. Moreover, we will make an extra effort to schedule a likewise important number of B-rated projects should these excellent January conditions last for another couple of weeks. Projects falling in a favorable LST range are likely to be observed.

The interferometer was moved to the B configuration - the most extended six antenna configuration planned for winter 2001/2002 - already at the beginning of January, two weeks ahead of schedule. We plan now to move early in February to the C configuration, but we will not change the interferometer configuration to D before the end of the month. So far, projects for the D configuration - the most compact - will not be worked off before mid March.

Investigators who wish to check the status of their project, may consult the interferometer schedule on the Web at http://iram.fr/PDBI/ongoing.html. The page is updated three times a day.

Roberto NERI

New phaser and Lo-Q racks for 6 antennas

With the preparations for the integration of 6th PdBI antenna into the array, a new phaser and Lo-Q system has been installed for all antennas (Fig. 3). These components are essential in the signal transport between the antennas and the correlator.

The phaser rack delivers reference signals to the LO1 for fringe stopping and to the LO3 for fringe offset correction. It also takes care of cable length correction, Walsh function phase switching and total power measurement. For the 6th antenna this rack has been entirely re-designed using DDS technology and integrated PLL assemblies. It has replaced the previous system which has operated for 15 years. The 100 MHz reference system was rebuilt too, with a low phase noise design.

The system was transported to the PdB on October 4th and installed as a ``plug and play'' device. Commissioning took longer than planned due to the manpower limitations on the site (and antenna 6 being in the final construction stage).

The whole system was eventually put into service, after a few hardware and software bugs were fixed. The performance was found substantially better than the previous system, essentially in the ``cable phase vs. time'' domain, (which was altered before by 0.05 degree oscillations), as shown in Fig. 4.

Marc TORRES

  

Figure 3: View of the new Phaser and Lo-Q racks, installed in the PdB coaxial cable terminal.

  

Figure: Actual length variations of a building-to-antenna coaxial cable. Vertical scale is 10 millidegrees per division @ 1875 MHz, equivalent to 1.8 micrometers on a 300-m length. Jumps are related to antenna motion. Quantisation steps of the digital phase meter can be seen at the $\approx 1$ millidegree level.