Notes for V2C telecon, Thursday Aug 30, 2012 -------------------------------------------- Attendance: Arthur Niell, Bill Petrachenko, Brian Corey, Chris Beaudoin, Dan MacMillan, Gino Tuccari, Jing Sun, Ruediger Haas, Tobias Nilsson, Jim Lovell (but with Teamspeak problems) 1. Broadband system developments and tests (Arthur, Chris, Gino,...) Significant progress has been made toward end-to-end (schedule to analysis) execution of a VLBI2010-style observing session. The June session was 6-hours in length between GGAO12 and Westford using broadband systems with frequencies set near 3, 5, 7, 9 GHz to avoid RFI and optimally set for phase resolution. The schedule used 50 sources, a minimum scan length of 30-s for a total of 180 scans over the session, i.e. one every two minutes. The session was run automatically using scripts but without the field system which still needs upgrades for the new equipment. Ed Himwhich is working on it. There were a few issues with scheduling plus problems with RFI from the SLR-radar for a total of 100 successful scans. SNR's were close to those predicted with a minimum of about 19 per band. FORFIT was used successfully to combine all four bands and both polarizations producing delays, delay rates, and (new to broadband processing) ionosphere values. The delays and rates were processed by Arthur using Sergei Bolotin's Nu-Solve analysis software resulting in 10-ps post-fit residuals. Since the phase delay errors were of the order 1-ps, a significant chi-squared adjustment was required. ' However, the residuals appear to have mainly random behaviour. Interestingly, analysis of Pcal data indicated a system delay azimuth dependence at GGAO12 (LMR-400 pcal cable or fiber?) and showed higher than expected temperature dependence of the system phase (UDC's?). An upgrade of the signal chain at GGAO12 is well on the way. The problem being solved is related to dynamic range issues in the RF over fiber down-link. Broadband is being separated into hi and lo bands with the lo band coming down on LMR-400 and the hi band still using fiber. The band cross-over is at about 4-GHz. The Westford receiver has be rewired to minimize longer runs of Teflon cable. Ground testing indicates significant noise temp improvement reaching close to theoretical expectations. The GGAO12 receiver positioner upgrade is progressing slower that expected. Mk6. Roger Cappallo has taken over the Mk6 software development tasks after David Lapsley's departure. He decided that a complete rewrite of the software was required mainly to improve reliability. Performance on the rewrite has reached 8-GHz and first on-air tests are expected in a month or so. In themeantime Mk5C's are being used. The DBBC3's have been under development for just over a year. These systems are for direct sampling of the RF signals and separation into bands. Slightly different versions are being developed for VLBI2010 and EVN. Sample rate is 28-Gsps and bandwidth is 14-GHz for full compatibility with VLBI2010. There are 3 components: the sampler, the Core 3 board, and the FILA40G card which is essentially a data collector. The FILA40G card can send data to different destinations, can do packet filtering, and buffering (e.g. burst mode). Its 40 Gbps capability will handle the max 32-Gbps output rate of VLBI2010. As far as DBBC2 firmware is concerned, the 1-GHz version has been developed for 15 64-MHz bands. The use of 64-MHz bands is more efficient wrt FPGA resources and can be made compatible with the usual 32-MHz bands due to the way software correlation is handled. Some concern was expressed about the wider channels wrt RFI avoidance especially at S-band. 2. RFI (Bill, Chris, Brian) Larry Hilliard at GGAO is testing materials for barriers between the VLBI antenna and colocated SLR radar and DORIS transmitter. He is looking for materials that are good absorbers. 3. Source structure (Richard, Arnaud) - (***postponed due to IAU***) Richard Porcas submitted a successful proposal for Eff+VLBA to observe core shifts in 7 ICRF2 sources. The observations are scheduled for September. Work has already been done using the EVN to select reference sources within 1 deg of each target source. 10 candidate reference sources were evaluated per target source and on average 2 good ones were found per target. 4. Full automation: schedule -> final products (John) An effort is underway to upgrade and automate the whole process from scheduling to analysis. Part of the upgrade is to fully accommodate all features of broadband observing. A significant upgrade to VEX is required and a committee is now defining VEX2. 5. Optimum schedules (Jing Sun, John) A new version of VieVS has recently been released. As before its main goal is the generation of optimized schedules. Recently the emphasis has shifted to operational validation. In particular, the VieVS scheduler has been used to schedule IVS RD "gamma" sessions which focus on sources near the sun. Feedback from stations has been useful for improving the software. Jing would like to apply her software to VLBI2010 schedules. 6. Antenna deformations and site ties (Dan) An engineer from JPL has been asked to develop an error budget for inter-technique vectors at multi-technique sites. Dan has been asked to provide error sources for VLBI. These include gravitation and thermal deflection of the antenna structure, atmosphere, clocks and observation noise. For gravitational deflection Dan is basing his estimate on the work of Perquido Sarti et al but reducing the numbers since the VLBI2010 antennas are expected to be stiffer than the Italian antennas studied. It was asked whether it is known how much bearing tolerances can contribute to time-variability in antenna positions. A mechanical engineer soon to arrive at Haystack may be asked to look into this. 7. Atmosphere (Johannes) - (***postponed since Johannes can't attend***) 8. TecSpec post-mortem - Feed summary: The comparison is waiting for specification parameters for the QRFH so that Miroslav Pantaleev can carry out efficieny simulations for QRFH and Eleven feeds on the Intertronics antenna. Data sheets for each of the feeds have also be requested. These are still outstanding. - DBE summary: Information for the RDBE, DBBC's, and UDC is essentially complete. Much remains to be filled in for digital back ends from Japan, China, and Russia. Gino will request the additional information. - RFI survey: RFI data has been received from 6 sites. Initial impression is that RFI will not often saturate receivers although significant regions of the spectrum will be rendered useless for VLBI2010. Detailed analysis is yet to be done. 9. Wiki progress (Brian) Beta testing (Bill) on site access is complete. Brian will send instructions to V2C members in the next few weeks for accessing the site. Next telecon: Sept. 27, 2012.