VLBA Data Quality Issues - 2000JUL01 through 2000DEC31 The following list is meant to be of assistance to observers and scrutinizers in assessing the quality of their data, and, as a supplement to the VLBA operators' log. It is not meant to replace the log, for data quality issues such as weather, tape readback results, power, communications, cryogenics failures, etc. are noted there and will not be repeated here. Information on RFI can be obtained via the VLBA home page and generally will not be noted here, unless an internal source is suspected. In the future, this page will be expanded to include links to plots that demonstrate the problem noted. If you have any questions or comments about this list, please contact Peggy Perley (pperley@nrao.edu) 505-835-7214. Station Timerange/Maint ID Problem/Fix description ------------------------------------------------------------------------------ Saint Croix - 00JUL09 (or earlier) BBC 1 filter problem causing channel to 00OCT19 amplitude to rise in the upper 25% of C102793 the bandpass. Fixed after BBC swap.(?) - 00JUL08 to 00SEP08 BBC 8 bit counts out of range. C102725 Fixed after BBC swap - 00AUG21 to 00AUG25 Shutdown site (hurricane Debbie) C102822 No damage - site restored to full operation - 00SEP01 to present RFI at 1483.99MHz (+/-8MHz) under investigation C102916 possibly due to new Caribbean broadcast sat. - 00DEC15 to present 13cm LCP FET voltage lower than expected. C103790 Data loss minimal for now, but receiver swap needed ********************************************************************************* Hancock - 00JUL to 00OCT05 4cmSX pointing appears to have an elevation C102991 dependency of +/- 1 arc-minute, with the extreme errors at low and high elevations. Techs report bubble in dichroic panel. Panel replaced 9/21/00. Problem did not clear. Techs then adjusted tension on ellisoid arm. This cleared the problem. ********************************************************************************* North Liberty - 00SEP11 - 00OCT16 20cm receiver damaged when compressor A C102988 failed. Awaiting new receiver. New receiver installed but problems persist. Problem resolved with receiver swap on 10/16/00. 00NOV29 - present 13cm LCP tsys higher than expected by 30% C103763 00DEC16 - 00DEC20 Az.#1 fuses blown (6) - replacements being C103805 being shipped ********************************************************************************* Fort Davis - 00JUL - present Random, sudden jump in pcal phases, unrelated to power outages,etc. Occurs ~ 2x/month L110 replaced, but problem recurs. - 00JUL - 00OCT12 4cmSX pointing appears to have an elevation dependency of +/- 1 arc-minute, with the extreme errors appears at low and high elevations. Tiger team reports cracks in dichroic surface. Awaiting dichroic panel replacement. Panel replaced 10/11/00. Tension in ellipsoid arm adjusted 10/12/00. - 00JUN? to present 'notch' in bandpass plots at 22241.49 and 22256.38MHz. C103378 - 00NOV06 - 00NOV27 ACU screen indicates az tracing error of > 20"; pointing C103462 test indicates data not affected.Problem resolved when az drive cabinet interface board replaced. ********************************************************************************* Los Alamos - 00JUN - present 13cm RCP/LCP tsys jumped slightly for no C102869 apparent reason. Receiver still useful - no plans to swap. - 00AUG - 00SEP21 2cm LCP tsys 75% higher than expected. C102866 Problem fixed with receiver swap. - 00SEP13 BBC 7 unable to lock at any frequency C103007 due to MCB problem. Problem cleared when MCB reset/BBC reseated. - 00SEP01 - 00OCT10 Cable cal measurements show scatter. C103089 Round trip phase module (L102)swapped. - 00OCT18 - present Metal flakes found in elevation bearing grease during routine check - change in bearing needed, and will require LA to be out of service for an extended period. 01JAN08-12 scheduled for repair work. Antenna will stay in service until then. - 00NOV16 - 00NOV22 ACU screen indcated az tracking errors;pointing test C103545 indicates data not affected. Problem cleared when AES and and ANC numbers in ACU re-entered. - 00NOV26 - 00NOV30 BBC 7 total/switched powers very low. C103631 Problem cleared when BBC replaced. - 00DEC08 - 00DEC13 Az#2 wheel axel broken - antenna un-useable. C103746 ********************************************************************************* Pie Town - 00AUG - 00SEP06 13cm LCP total powers varying 5x greater C102897 than RCP. Receiver replaced. - 00JAN - 00OCT04 False position errors originating in the ACU C10185,C103097 causing data to be flagged incorrectly. Numerous ACU boards replaced, problem disappeared.See maint form for more details. ********************************************************************************** Kitt Peak - 00JUL20 - 00SEP07 -2.5arc-minute tilt offset at 35d elevation C102944 accidently entered in ACU during major maint visit affects pointing on all sources observed between 30-40d elevation. - 00JUL(?)- present BBC 5 bandpass 'flat' - BBC swap planned. C103377 - 00AUG - present 1cm (maybe others) bandpass plots have a C103379 'wiggle' - under investigation. ********************************************************************************** Owens Valley - 00JUN - 00NOV29 Random, sudden loss of pcal phases, with C102272 recovery just as sudden. Occurs rarely, less than 1x per month. L110 swapped out, still recurs, albeit rarely. Problem not seen in 4+ months, so flrm closed out. Recurred 12/28/00. - 00AUG01 - 00AUG08 4cm LCP problem with FET voltage - data bad C102676 periodically.Problem fixed when receiver replaced. - 00SEP12 - 00SEP16 Az. motor broken - antenna unavailable. C102989 - 00DEC13 - 00DEC14 AZ. overcurrent faults/fuses blown C103772 ********************************************************************************** Brewster - 00JUN - 00AUG03 Dew point measurements tracking Temp., causing inaccurate atmospheric corrections. Problem eliminated when mirror cleaned and unit re-calibrated. - 00JUL - present 1cm elevation pointing dependency curve is quite under investigation different from 7mm, when we expect them to be similar. - 00AUG22 - 00OCT10 ACU message indicating antenna not pointing. C102837 Antenna recovers point mode on its own within seconds. Does not appear to be affecting data at the present time. - 00JUL - 00AUG28 2cm RCP problem with FET voltage - data C102836 bad periodically.Fixed when receiver replaced. - 96JAN - present 7mm sensitives 50% less than expected due C100766 to poor panel adjustment. - 00SEP09 - 00OCT18 7mm LCP problem with FET voltage following a C102990 compressor failure and receiver warm up. Awaiting receiver swap. Receiver removed on 9/18/00 when it was determined that it would be quicker to repair this unit rather than repair the spare. Both RCP and LCP dead in this period. *********************************************************************************** Mauna Kea - 00JUL06 -00AUG16 Bad cable connecting IF distributor 2 to various IFD was the ultimate culprit responsible for several write ups concerning bad data on IFs C and D. Two swaps of the IF distributor units failed to clear the problem. Cable replacement cleared problem. - 00SEP21 - 00OCT26 Recorder 1 miscalibration causing head pos. -319/+319 various to overwrite adjacent passes. Affects only 128Mbit/sec projects. - 00OCT30 - 00DEC21 7mm LCP FET broken during cryo warm-up. Awaiting C103436 amplifiers to fix spare. New receiver installed 12/21 fixed problem. *********************************************************************************** VLA - ? to present notch in BBC bandpass plot under investigation Software