From fghigo@nrao.edu Tue Apr 27 10:10 MDT 2004 Date: Tue, 27 Apr 2004 12:09:53 -0400 From: Frank Ghigo User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.0.2) Gecko/20021120 Netscape/7.01 X-Accept-Language: en-us, en MIME-Version: 1.0 To: Craig Walker CC: Paul Kondratko , VLB operators , analysts , gtaylor@revere.aoc.nrao.edu Subject: Re: BK110 References: <200404261742.i3QHgSms016862@cfa.harvard.edu> <408E7C2F.9000701@nrao.edu> <408E807E.3090600@aoc.nrao.edu> Content-Transfer-Encoding: 7bit X-MailScanner-Information: postmaster@gb.nrao.edu X-MailScanner: Found to be clean X-MailScanner-SpamCheck: not spam, SpamAssassin (score=-6.3, required 7, BAYES_01 -5.40, EMAIL_ATTRIBUTION -0.50, QUOTED_EMAIL_TEXT -0.38, REFERENCES -0.00, REPLY_WITH_QUOTES 0.00, USER_AGENT_MOZILLA_UA 0.00) X-Lines: 101 Status: RO Craig, The best advice on move times is in the web page http://www.gb.nrao.edu/~fghigo/gbtdoc/vlbinfo.html#moving Our move times for short moves could be improved by better algorithms for the servo system, and this may happen some day. The elevation slowdown should not have been a problem, since the source and calibrator were at practically the same elevation. The accelerations did not change. Setting TSETTLE to 20 sec would probably be prudent. -- frank Craig Walker wrote: > The source change is rather longer than the SCHED prediction of about > 19 seconds, even after the adjustment to the 9 deg/min slew rate in > elevation. The acceleration was not adjusted from the 0.05 deg/sec/sec. > Did that change enough due to the motor problem to account for the > discrepancy? Otherwise, do we need to change TSETTLE or some other > parameter? Is there much lag between the end of a scan and the start > of a slew? > > Note for RA, the original AX1RATE=36 and AX1ACC=0.05 were used. > TSETTLE=5.0 was also used. > > We should try to understand the slew calculation discrepancy because > phase referencing will be a common mode. > > Craig > > P.S. We did have a bit of a scare at the start of the run when only > one tape drive started up despite SCHED's commands to run both. The > on-line system, I guess, noticed that it would not be recording > anything on the second drive for the 64 Mbps section so it did not run > the tape. We were a bit nervous about what would happen when it > finally did need the second tape, but all went ok. > > A lesson of this incident is that dropping below 128 Mbps in a 512 Mbps > observation does not save any extra tape. > > Once we have Mark5 all such issues will go away, I sincerely hope and > expect. > > > > > Frank Ghigo wrote: > >> VLBI project BK110, using K-band, was observed at Green Bank. >> Things went fairly smoothly. >> Initially the weather was cloudy. A tipping scan done in the >> previous K-band observing run showed an atmospheric tau of ~ 0.12. >> The weather gradually cleared up. >> >> Prior to the start, we did some pointing on very strong sources, >> Jupiter and 3C84. At first the peaks looked bad, with prominent >> side lobes on the beam and poor gain. Possibly the active surface >> was not functioning. We looked at the active surface cleo screen >> and verified that it was indeed active. After that, the peaks >> looked good and had no sidelobes. Had the active surface >> suddenly awakened? >> >> We joined the schedule at 23:06 UT, a little late because of >> fooling around with pointing and focussing. All subsequent scans >> were observed. >> >> Kevin ran the pointing checks imbedded in the schedule and all >> those worked ok and good fits were found. The dynamic corrections >> were being used. >> >> The pointing corrections were as follows: >> Source Elev UT NewAz2 NewEl >> 1124-186 24 00:10 0.096 -0.076 >> 1124-186 31 01:22 0.107 -0.185 >> 1045-188 30 02:55 0.119 -0.152 >> 1045-188 25 03:53 0.115 -0.140 >> >> The cycling time between source and phase calibrator was >> 40 seconds for a large part of the run. It typically >> took 30-35 seconds to change sources (the two sources >> were separated by about 2.5 degrees with most of the >> move in RA). Thus there were about 5-10 seconds of >> on-source time for most of the observations. >> This seems pretty short to me, but maybe that is what >> you wanted. >> >> The tapes will be shipped to Socorro today. >> >> -- frank >> >>