LOG OF ADJUSTMENTS TO SAO maser at NRAO-Green Bank (140-foot CONTROL BUILDING.) ------------------------------------------------------------- Date Changed UT Synthesizer Fine Tuning* 1PPS delay ----------------- --------------- ------------ ---------- pre-July 1992 0405751.691 Hz 49 ?? 23 July 1992 0405751.691 Hz 45 ?? 29 Jan 1993 0405751.692 Hz 62 ?? 8 Feb 1994 0405751.693 Hz 51 913240 2 Aug 1994 1400 0405751.693 Hz 94 913230 us 24 May 1995 " " 830834 us 26 Jul 1995 1400 " " 830844 us 5 Aug 1996 1400 " 99 298535 23 Oct 1996 ?? 0405751.694 37 298528 us 15 Apr 1998 2000 0405751.696 37 ? ------------------------------------------------------------- * Top dial reading. Notes: 21 Feb 1995: Vac-ion pump tripped breaker; maser re-started, 1 PPS offset adjusted. Synthesizer and fine tuning not changed. 22-24 May 1995: Vac-ion pumps replaced. Maser being worked on May 22-24. Synthesizer and tuning not changed. 1pps delay adjusted. 26 July, 1995: change 1pps delay by 10 microsec to make ST-SAO-12.3 us ~0 31 July,1996: power supply fail on LO, 1pps box, 5MHz distributor. Vance&Beale change coarse tuning +.001 to get LO to lock. Rate 25 usec per 4 days drift wrt GPS. 5 Aug, 1996 Restore Synthesizer to prev value (...693) Adjust 1pps delay to near 1us as read at 140ft. 23 Oct 1996. Adjust rate to match GPS. Adjust offset to give corrected offset to GPS less than 1 us. November 1997: Vac-Ion pumps tripped breaker. Temp fix of vac-ion pumps by use of ball-peen hammer. March 30, 1998: Don Graveline visits and changes the vac-ion pumps. April 1, 1998: Maser moved back to 140-ft building. 1pps offset adjusted. April 15, 1998: maser synthesizer adjusted to match ST maser rate: previous synthesizer: 405751.694 Rate offset measured with the "frequency standards comparator" 100ps drift in 68 seconds --> 1.47e-12 Increase counter by .002 --> new rate offset is 5e-14. Fine adjustment (dials) not changed.