LOG OF CHANGES OR PROBLEMS IN TIME MEASUREMENT AND CLOCKS AT NRAO-GREEN BANK. ----- 1994 --------------------------------------------------------------------------- Date UT Comments ------ ----- ------------------------------------------------------------- 6 Jan 14:50 adjust sigma tau synthesizer (see STmaser.log) 31 Jan adjust ST offset (see STmaser.log) 8 Feb 15:30 adjust SAO maser (at 140-ft) synthsizer to match GPS rate. Adjust 1pps offset to give < 2us wrt GPS. 21 Feb 17:00 HP time interval counter broken 25 Feb 18:00 HP counter fixed, but negative readings erroneous. (affects GPS-ST, GPS-P3) 2 Mar 21:00 HP counter 10 MHz reference connected, good readings now. 4 Mar 15:00 Power out. 1 MHz ref for GPS lost. GPS reading erroneous. 5 Mar 21:00 GPS has recovered correct timing. 4-5 Apr GPS glitch - data bad from 13:59 Apr 4 to 19:00 Apr 5. 13-14 Apr GPS glitch - data bad from 07:00 Apr 13 to 04:00 Apr 14. 28-30 Apr HP9915 hung up - no data from 1400UT Apr 28 to 1500UT Apr30. 02 May Installed upgraded chips in DATUM GPS receiver - ignore data from 1600 to 1700 UT. 03 May 1400 Adjust ST synthesizer and 1pps offset (see STmaser.log) 03 May P3 maser power supply being worked on - ignore P3 data from 1600 to 2000 UT. 17-19 May Power off timing rack while UPS being tested. Sigma Tau offset and Loran data erroneous from 16:50 UT on May 17 to 19:00 UT on May 19. GPS and P3 data ok. 18 May HP9915 hung up - no data 06:00 UT May 18 to 19:00 UT May 19. 19 May Sigma Tau 1pps offset changed - 19:00 UT. (see STmaser.log) 20-25 Jun Problems with modem and serial port used for downloading timer data. Several days with no data being saved. 27 Jun 11AM VHF switches B1,B2 not working. Swapped GPS with LORAN. Now *-LORAN is really *-GPS. 28 Jun 3PM VHF switches B1,B2 still not working. CHanged B3 to ST. and B4 to GPS. 14 Jul 17:20 Replaced VHF switch with spare unit from USNO. Switch connections back to pre-June 28 arrangement. --------------------------------------------------------------------------- 1995 May 1995 - HP9915 computer has broken. Do not plan to fix it, because GBT timing system is now in place. Refer to Gtimer.log and README.* files for information on the new system. The old HP-based system is now retired. 1995 June 18, 1996 - adjust 1pps offset. ------------------------------------------------------------------------- APPENDIX: FORMAT OF *.TP FILES =============================== ----------------- 49504.0833333 Modified Julian Date (=JD-2400000.5) [June 1, 1994} 200 UT time: hhmm or hmm [02:00 UT] .999998704 VSYNC - ST : all time intervals in seconds. .999999585 VSYNC - GPS .000009729 VSYNC - P3 .044008137 VSYNC - LORAN .000000002 ST - ST .000000879 ST - GPS .000011027 ST - P3 .044009437 ST - LORAN .999988976 P3 - ST .999989854 P3 - GPS 0 P3 - P3 .043998411 P3 - LORAN .9999988 VTIME - ST .999999677 VTIME - GPS .000009823 VTIME - P3 .044008234 VTIME - LORAN 99600.4 Loran Chain .04400868 Loran Offset ----------------- --------------------------------------------------------------- Explanation of codes: VSYNC : "sync" output from VLBA DAR rack. ST : 1 Hz derived from Sigma Tau maser at Interferometer. P3 : 1 Hz from SAO maser at 140-ft VTIME : output from VLBA timing module in DAR rack. GPS : 1 Hz output from GPS receiver. LORAN : 1 Hz output from Loran receiver. --------------------------------------------------------------- APPENDIX C: FORMAT OF *.TP FILES June 27-28, 1994 =============================== ----------------- 49504.0833333 Modified Julian Date (=JD-2400000.5) [June 1, 1994} 200 UT time: hhmm or hmm [02:00 UT] .999998704 VSYNC - --- not working .999999585 VSYNC - --- not working .000009729 VSYNC - P3 .044008137 VSYNC - GPS .000000002 ST - --- not working .000000879 ST - --- not working .000011027 ST - P3 .044009437 ST - GPS .999988976 P3 - --- not working .999989854 P3 - --- not working 0 P3 - P3 .043998411 P3 - GPS .9999988 VTIME - --- not working .999999677 VTIME - --- not working .000009823 VTIME - P3 .044008234 VTIME - GPS 99600.4 Loran Chain .04400868 Loran Offset ----------------- APPENDIX D: FORMAT OF *.TP FILES from 19:00 UT June 28, 1994 to July 14, 1994 at 17:10 UT =============================== ----------------- 49504.0833333 Modified Julian Date (=JD-2400000.5) [June 1, 1994} 200 UT time: hhmm or hmm [02:00 UT] .999998704 VSYNC - --- not working .999999585 VSYNC - --- not working .000009729 VSYNC - ST .044008137 VSYNC - GPS .000000002 ST - --- not working .000000879 ST - --- not working .000011027 ST - ST .044009437 ST - GPS .999988976 P3 - --- not working .999989854 P3 - --- not working 0 P3 - ST .043998411 P3 - GPS .9999988 VTIME - --- not working .999999677 VTIME - --- not working .000009823 VTIME - ST .044008234 VTIME - GPS 99600.4 Loran Chain .04400868 Loran Offset -----------------