VLA/VHF Program Update 2005 June 13 Recent and Upcoming Events/Milestones May 18 Installation of 2 MHz front-end filters (195.4 MHz band-center) completed on each antenna, enabling up to 4 station interferometry in one polarization and 2 station interferometry in dual polarization. The filter passband lies between audio and video carriers for channel 10, in a relatively "clean" part of the RFI spectrum. Time variability and strength of RFI in this band is low enough to enable useful total power measurements at night, and interferometer measurements during day or night without destabilization of the VLA autogain control system. May 20 First daytime synthesis point-source image (3C147; 8 minutes). May 25 Second determination of 2m system impact on L-band performance of VLA antennas (less than ~ 1% impact on Tsys and gain). Negligible impact on L-band performance has been a key goal. May 27 Receiver 2 (antenna 6) returned to Cambridge for repair due to low fringe amplitude and to provide a lab test system. A three antenna subarray remains deployed. May 31 Initial discussions with KCHF, DTV channel 10, which is building a 30 kW transmitter near Santa Fe to come on line by 2006. Our desire to coordinate VLA operations w/ transmitter operation very late at night was received with some optimism that arrangements will be possible. Further discussions are anticipated in fall 2005. June 1 Proposal submitted for 750h (3 sources) in the 2007 D-array. In late 2004, 150 hours were approved for the 2005 D-array. Observing time in 2005 and 2007 is contingent on 2m system system performance. June 1-3 First nighttime synthesis images. System equivalent flux density for _prototype_ receivers is ~ 3700, consistent w/ Tsys = 200 K and efficiency = 0.3. First measures of interferometric cross polarization are ~ 20%. Educated guessimates of nominal SEFD in proposals for observing time have been on the order of 2200 Jy. Improvement can be anticipated with deployment of production receivers, but achievement of reasonable sensitivity is a big step toward a second key goal of the project. June 3 Determination of 2m system impact on P-band performance of VLA antennas (7% +/- 5% improvement in gain and 10% improvement in primary beamwidth). Low impact on P-band performance has been a key goal. Observed improvement in performance is good fortune. June 15 Field testing of a Yagi-style director antenna to boost 2m gain and reduce horizon response to RFI. Lab measurements predict a ~ 9 dB reduction in feed response at the edge of a VLA dish. Sept 1+- SAO internal R&D proposal deadline to support continued manufacture and deployment in early FY06. Socorro Travel May 31 - Jun 3 Greenhill Jun 14 - Jun 17 Greenhill Other Travel May 27 - 9/1? Carilli to Bonn, Humboldt/MPI fellowship Jun 25 - Jul 2 Greenhill to Reionizing the Universe conference in Grongingen Dec 7 - 10 Greenhill to Tasmania cosmology meeting Notes and Details There are three key goals of the field-testing: demonstrate adequate sensitivity for the proposed key science, formulate a plan for RFI mitigation, and demonstrate that the 2m system has no significant negative effects on users at other wave bands. Field-testing has attacked each of these, making very substantial progress. A go/no-go decision will be made in late June, following internal review of field testing results. This will be followed by an NRAO panel review that will assess design and performance. Redesign and optimization of receiver system components to determine how well issues observed during field testing can be addressed. One critical performance element is system temperature/antenna coupling. These are being balanced against needs for (1) robustness to mismatch between the dipole feed and receiver, (2) amplifier stability and high gain, and (3) cal injection as close to the feed as practical, among other factors. The overall goal of the program is full deployment by not later than December 1. Deployment of two receiver systems per week is consistent with experience gained in fieldwork, and full deployment would require ~ 14 weeks. Procurement and production to meet this deployment schedule will be complicated by lead times for components and manufactured parts (e.g., circuit boards, dipole hubs). Orders may have to be divided into rush and nonrush batches. Macos Diaz (BU graduate student in astronomy) will continue work with the VHF project in June and August. His current work includes modeling notch filter response, which is critical to design of an inexpensive network of high-Q crystal devices that may be used to damp the effects of TV carriers. Lauren Peritz (Cornell engineering student) has joined the project for June and July. She has begun with work on the temperature control circuit to be used in a production receiver design and with work on lab characterization of the Yagi director test assembly. Welcome Lauren! One or two additional slots will be filled for work during the summer and fall on testing and assembly of receivers.