V2C Telecon Notes, Thursday Nov 1, 2012 ---------------------------------- In attendance: Bill Petrachenko, Arthur Niell, Zinovy Malkin, Jing Sun, Johannes Boehm, Brian Corey, Gino Tuccari, Mamoru Sekido. Ruediger Haas and Miroslav Pantaleev could not attend but sent a short report: - Miroslav has been working on the QRFH and Eleven feed efficiency simulation (assuming the feed is on an Intertronics antenna). The work is nearly complete. - Miroslav is also working on an RFI survey at Onsala and will report shortly. - Ruediger has been experimenting with twin telescope scheduling using VieVS and has not been satisfied with the performance of VieVS. He was wondering if John Gipson is considering developing an extension to Sked for twin telescopes. [Johannes responded in the telecon that the twin telescope algorithm in VieVS is still preliminary and more work needs to be done.] - Ruediger has also been working with Michael Loesler from BKG on a manuscript concerning automated and continuous monitoring systems for radio telescopes. It will be submitted in December. 1. Who has been using the Wiki? How many have accounts? (Brian) Eight users have signed up for the Wiki - 3 from MIT and 5 others. Only 3 have actually made changes to the Wiki. Brian also enquired about limitations related to the size of files. He was informed that problems begin at about 1 Gbyte and are not predominantly related to memory size limitation but more to a slowing of the Wiki. It was asked if a server is available where VLBI2010-related files can be stored so that links in the Wiki can be used. It was pointed out that any anonymous ftp site should work. 2. Broadband system developments and tests (Arthur, Chris, Gino,...) Chris Beaudoin and four others are currently at GGAO12 installing upgrades. The upgrades predominantly include a new feed/dewar package mounted nicely on a platform that can be retracted automatically for servicing. Arthur wasn't sure if the predictability of positioning was accurate enough for focus setting. The new package includes a Monitor Control Interface (MCI) to keep track of a wide range of voltages, currents, temps, etc at the front end. The new system includes noise cal injection that supports synchronous detection and and remotely controlled digital step attenuators are being added to the PCAL and noise cal inputs so that level can be controlled remotely. Tsys measured on the ground for the new receiver package was very good. Measurements on the antenna are expected in the next few days. In addition new downlink circuitry is being installed to avoid saturation of the link by RFI. The down link will be split into two bands, lo=2-5 GHz and hi=4-14 GHz with the lo band coming down on low loss coax and the hi band on fiber. This will make possible the removal of the 3.5 GHz low pass filter so that operation at S-band can be tested. At Westford, the cal box will be replaced by the cal box previously at GGAO. The next observations are planned near the end of Jan. This will be an R&D observation to evaluate interactions between S/X and broadband data. More has been done in the analysis of the October data. For the obs on Thur a 40 degree circle around the SLR direction was masked during scheduling to avoid saturation or damage due to the radar. For the obs on Friday, the SLR radar was off. There was about 33 scans per hour limited mainly by slew speed of GGAO. Due a problem with one polarization, about 30% of the data was lost. A full end to end broadband observation was carried out with Dave Gordon using the total intensity (I) observations in SOLVE. Post-fit residuals were about 10-ps for Thur and a little larger on Fri. Single obs delay precision was on the order of 1 ps due to high SNR. Single band BW was 512 MHz throughout and the freqs were placed at about 3.5, 5.5, 6.5, and 9.5 GHz. GGAO efficiency was about 65% in the freqs observed. Westford was nearer 20% but the reason for the low efficiency is still not understood. 3. RFI (Bill, Chris, Brian) Bill and Brian began analysis of the RFI survey data sent to the V2PEG. For all of the sites that we've looked at, it appears that RFI will not saturate the front ends most of the time - but at many sites there is little margin. More quantitative analysis will continue and a report is being organized. 4. Source structure (Richard, Arnaud) - new directions for simulations at Bordeaux? Arthur Niell contacted Roopesh Ojha after the telecon and along with a graduate student Bryce Carpenter tentative plans have been put in place to make a proposal to VLBA by Feb.1 for source structure related observations. In addition Arthur is considering observations with the GGAO12 - Westford baseline to study structure phase but as yet the process is not fully developed. 5. Full automation: schedule -> final products (John) VEX2: A meeting was held with Walter Brisken, Ed Himwich and Alan Whitney to resolve issues with the VEX2 definition, which is required to automate the processing path from schedule to final products. Progress was made toward finalizing the definition. 6. Optimum schedules (Jing Sun, John) - mixed schedules? The mixed scheduling mode was investigated by Jing Sun. There are two approaches, either using completely separate sub-nets, one for S/X and one for broadband or alternatively using mixed scans. In the mixed scans mode, the schedules are degraded by the S/X stations due to the requirement for longer scans to make up for the reduced S/X bandwidth and data rate. 7. Antenna deformations and site ties (Dan) 8. Atmosphere (Johannes) 9. TecSpec post-mortem - Feed summary - DBE summary - RFI survey Notes from Japan: A small diameter antenna system is being put together that is semi VLBI2010 compliant. The semi refers to the fact that the system will use fixed frequencies. Fixed frequency down-converters are being put together along with direct sampling. _______________________________________________ IVS-v2c mailing list IVS-v2c@ivscc.gsfc.nasa.gov http://ivscc.gsfc.nasa.gov/mailman/listinfo/ivs-v2c