V2C Notes, Thursday Dec 20, 2012 ---------------------------------- In attendance: -------------- Chris Beaudoin, Brian Corey, John Gipson, Chopo Ma, Arthur Niell, Bill Petrachenko, Mamoru Sekido, 1. Broadband system developments and tests (Arthur, Chris, Gino,...) -------------------------------------------------------------------- Note from Gino: --------------- - DBBC3 is progressing - Broadband receiver is under construction (Bill's note: we assume for Noto) - Performed an RFI survey in Noto (pretty good for frequencies above 2.4 GHz in the entire range) Arthur reported progress in processing the Oct 4,5 broadband data: ------------------------------------------------------------------ The data was processed in three ways: H-pol with no ionosphere correction; V-pol with no ionosphere correction; total intensity (I) with ionosphere correction. Baseline was estimated (N E U) along with piece wise linear clocks and atmosphere using ~20 minute intervals. The polarization results agreed with eachother at the 1-3 mm level while the I solution differed between days by about 5 mm. Based on pcal data it appears that cable delay has ~30 ps azimuth dependence at Westford. Further work will include application of PCAL phase offsets, an a priori cable model, and a stochastic atmosphere. Jan. 29 there will be an R&D session with GGAO and Westford in broadband mode plus 4 or so other stations. The goal is to gain experience with mixed broadband/SX stations. Brian reported on the cable delay issues: ----------------------------------------- Azimuth pcal delay dependence at Westford is about 30 ps p-p while at GGAO it is < 10 ps. The conclusion that the Westford pcal delay dependence is due to the uplink 5 MHz cable is based on the indirect evidence that the dependence is similar to Westford S/X dependence where a different cable (of the same type - LMR-400 ultra flex) is used for the uplink. The high level of dependence is somewhat puzzling since, based on evidence from AEER, the LMR-400 ultra flex is thought to be very stable wrt flexure. In fact it appears that the LMR-400 at Westford is much worse than the cable previously used for S/X. Further investigation is planned at both Westford and GGAO. Cable calibration using the Mk4 systems is not a good option since the ground unit is not precise enough and drifts. Higher frequency systems such as the Kokee fiber system and the VLBA system may be better alternatives. Mamoru Sekido reported that Takefuji-san is working on a reflection-based cable cal system and that the time and frequency group at NICT has developed a stable loop system using a modulated optics system. The latter option appears to work well but is a bit expensive at about $10,000. Chris reported on the GGAO upgrade: ----------------------------------- There are now 4 LMR-400 cables running to the focus at GGAO. The cables are about 250 ft long in total and have been checked out through the wrap. There were some problems communicating with the 4 attenuators in the RF signal path: pcal input, noise cal input, and H/V-RF input in the hi band. The latter two are required for dynamic gain ballancing for the fiber link. On the short term, fixed attenuators have been installed and the programmable attenuators have been returned to Hittite for investigation. Otherwise things look fairly good. Chris will return to GGAO next Thu/Fri for further testing and debugging. 2. RFI (Bill, Chris, Brian) --------------------------- Bill reported that progress is being made in the analysis and report writing for the V2PEG RFI survey. Chris reported that some progress has been made in simulating barriers for intra-site DORIS and SLR radar attenuation. Also, Larry has built a 4x4 test barrier and is setting up a fiber optic cable and network analyzer to carry out field experiments. Tests need to be carried out to see if there is enough SNR for the network analyzer. First tests will be carried out with standard gain horns. A spare radar horn is being loaned for the next level of tests. 3. Source structure (Richard, Arnaud) - new directions for simulations at Bordeaux? 4. Full automation: schedule -> final products (John) ----------------------------------------------------- John reported that automation of intensives is expected in the next year. He will also travel to Vienna at end of Jan. to be external examiner for Jing Sun. Arthur reported that a roadblock in the definition of VEX2 has been removed. The next version should be expected soon. 5. Optimum schedules (Jing Sun, John) - mixed schedules? John reported that some thinking has gone into mixed (broadband and S/X) schedules stimulated by the approaching mixed R&D expt on Jan29. Dan is doing simulations and the thought is to perhaps separate the schedule into 3-hr chunks with different philosophies. The problem is that the S/X stations significantly degrade mixed observations. Arthur thinks the Jan29 schedule will be generated as an S/X schedule resulting in very high SNR's on the broadband baseline and longer dwells than otherwise required. 6. Antenna deformations and site ties (Dan) 7. Atmosphere (Johannes) 8. TecSpec post-mortem - Feed summary - DBE summary - RFI survey 9. Wiki (Brian) Next telecon: Thursday, Jan 24, 2013. _______________________________________________ IVS-v2c mailing list IVS-v2c@ivscc.gsfc.nasa.gov http://ivscc.gsfc.nasa.gov/mailman/listinfo/ivs-v2c