Notes for V2C telecon, Aug 29, 2013 ------------------------------------ In attendance: Dirk Behrend, Johannes Boehm, Brian Corey, John Gipson, Jim Lovell, Chopo Ma, Dan MacMillan, Arthur Niell, Bill Petrachenko. Broadband developments: ----------------------- GGAO12: - The system is operational but with lower than expected gain in the low band. Not sure if this is cable losses or the LNA, but cable losses are probably ruled out. Sensitivity in the low band, however, appears to be nominal so this should not be a problem for observations. - Low band is also blowing fuses. The LNA and temp sensor has been replaced - Off line (non VLBI mode) testing in Sept is planned for: ~ diode control of synchronous 80 Hz TP detection ~ RDBE version 3.0 including PCAL ~ Mk6 recorders Kokee: - Broadband front end is under construction at Haystack. Completion expected in 1-2 weeks. Westford: - Dewar is being rebuilt for better illumination of the primary. Will continue after completion of Kokee front end. RDBE: - in addition to version 3.0, a quad 512-MHz system and dual 1024-MHz are under development. - Art visited Mo at Digicom. A new version of the RDBE using the Haystack Synthesizer and other off-the-shelf componensts (attenuators etc) will soon be available commercially. Analysis of May obs: - Work continues with determination of correlated flux densities. Since Tsys was not possible in May, calibration was done using CAS-A and system gain was assumed to be stable so that raw TP's could be used. Rms scatter in single channels is nominal (~10%) but there is an unexpected 10% bias between polarizations. Also, scatter for a full band is larger than expected. On the other hand, scatter for a full band using an alternate PCAL approach appears to be nominal. Work continues to better understand and improve processes for determining correlated flux densities. - No new observations are planned. However it was noted that the Master Schedule includes Westford/GGAO12 observations starting in Oct. This may be possible but not sure. Sterling Cycle front ends: - This cooperative effort between Callisto and Auscope has been going on for about a year. Cryo tests on a "Low Noise Factory" LNA have been carried out at Sterling Cycle temps and lower. T(LNA) looks good enough. Jim will look into circulated the results to the V2C - Scaled QRFH (2.3 to 14 GHz) delivery is expected soon. - Next step is the development of a full front end for testing on an antenna. This will cost 150K Euros which are not available at the moment. Jim Lovell has been exploring collaboration with New Zealand and Japan. Any other interested parties are encouraged to join in. RFI: ---- - RFI spectra produced by JPL were received from Goldstone. NASA Space Geodesy Project is considering a multi-technique site at Goldstone and is investigating RFI environment. The data are uncalibrated and would be more useful if absolute power levels were known. - Communication continues with La Plata to come up with a RFI monitor system that could be copied at or moved to other locations. No funds have been identified for this work. - Investigations into the use of barriers to attenuate intra-site (DORIS and SLR radar) RFI have begun but there is no recent progress. - Initial work has been undertaken to develop interlocked SLR/VLBI schedules so that antennas are never simultaneously pointing towards eachother. Source Structure: ----------------- - Dan has been working on simulations for the SGP system review in Oct. He has been looking at future networks in 2016 and 2020. When this is done he will have time to look at simulations to determine expected VGOS source positiond accuracies. - Johannes reviewed the source structure simulation work done by Stas Shabala. After the last telecon a memo was distributed to the V2C and a paper is in preparation. Actual CONT11 schedules were used. If atmospheric turbulence is set to zero and ICRF2 quality of sources are used, the contribution of source structure to position error is at th 1-2 mm level rms but could be as large as 5 mm. If turbulence is included, however, the degredation is much smaller. The error is systematic if the same schedule is used - but if different schedules are used the error is randomized. Automation: ----------- - Ed Himwich and Alan Whitney continue to work on the VEX2 definition. This is a 'high pole' for automation of the signal path so it is a priority. - Sergei Bolotin continues to automate the data path. Intensives will be automated first followed by R1/R4. Significant progress is expected by the general meeting. Antenna deformations: --------------------- - The 12m at Hobart has been outfitted with temp sensors and survey targets. They are ready to observe antenna deformations in the next few weeks. The finite element work is in an earlier stage. Atmosphere: ----------- A Swedish student, David Eriksson, has been at NVI doing work on ray tracing. Using a weather model provided by GEOS 5.9.1 (3 hour, 50 km, 72 levels) he has been able to show consistent improvement in CONT11 and R1/R4. Various weighting schemes have also been looked at. The impact of elevation cut-off is much reduced with ray tracing. Next telecon: ------------- The next telecon will be on Sept 26.