USNO VLBA Support Meeting

• Correlator:
• VLBA Status
  
  • Filter removal at SC & LA.
    • Strong RFI was seen
      • Craig: covered all possible settings and logical settings on LCP & RCP.
      • Craig: do not want to take filters out is tentative analysis.
      • Another test will be run with filters back in this coming weekend.
      • Another thing to look at is switchable filters for some observations that may not be as impacted by the RFI.
      • Chris: How narrow is satellite band? Craig: It happens with PFB that a single band contain it (I think 2320-2345).
      • There appear to be quite a few bands that appear to be useable. There is an upcoming observation (Burke-Spolaor) that is using these bands.
      • RFI is naturally directional.
      • There were a few cases (2210) where there were only LCP or RCP RFI spike. It suggests electronics hardware insertion.
    • Observation was archived for USNO, albeit in FTP site.
      • No analysis done yet.
      • Autocorrelations will be reviewed.
      • Developing an optimal frequency set is still the goal for USNO.
  • Data Quality Improvement
    • USNO Update on effect of 5MHz pulse cals:
      • Dan: Last meeting that was trouble extracting phase cal from baseline line data vs. post-HOPS fringe data. Dave spoke with Haystack and can now extract pcal from individual station files. This can be compared with DiFX produced data to compare for corruption.
      • Dan: We were comparing various Pcal data from VLBA data vs. IVS. VLBA was on order of 3-4 times higher rate. Dave: This is another Haystack question on how HOPS handles it.
      • For example, MK-PT: Pcal rates 10^-3, other IVS were 10^-7. May just be how HOPS handles Pcal. It looks similar to having a high clock rate at stations.
      • Craig: NRAO issue exists where some of the phase cals pulled out of DiFX differ compared to legacy correlation. A rapid wind has never been seen, though.
      • Walter: Can USNO plot the raw phase as a function of time? Dave, we should be able to once we can pull some out.
      • Craig: What can we use? Walter has a new tool that does this, but it is not archived. Station data is saved, though.
    • USNO Update to increasing cable cal measurement cadence
      • Chris: USNO is receiving the higher cadence cable cal data. Comparisons show that the data is the same but just more frequent. This shows more useful information. A test environment is being set up to determine impact on final result (compare no cable cal, low cable cal, high cable cal).
      • The values put out by NRAO in cal file are ~500 (picoseconds) for the cable. Once processed through cable calibration data for use by catalog system, the numbers are divided by 2,500,000. What is reason or source of this multiplication?
        • NRAO: Craig, unknown of source. Walter: We see a variation between experiments of ~30 picosec, leading to a bias of about 100 microsecs. A low cadence cable cal would not do much to resolve the 20 picosec scatter.
      • Walter: Another issue to watch: Occasionally cable cals are erratic, with a very incorrect outlier. USNO: those are removed.
• Daily Observation Report for September
  • Only on 17th (4260) where there were 2 runs before a 3 was good. But 2 scans in X were not used (but S was).
  • Dan: Once the observation gets through HOPS, there are various data quality codes applied. If some scans were flagged, they weren't exported at USNO, hence the lost of two X-band scans.
  • Chris: September was another good month as far as using exported data with very little extra work.
• Open issues
  • Chris: Looking at the databases, looking for issues or incompatibilities. Is 5454 revision still be run? Yes.
  • Quarterly report due soon. Ephraim will send out next week.
  • Next meeting on November 13th, 2014.