2016 December

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Dec 01

12:52 UT For the past several days we have done normal solar observing, with some interruptions due to testing new fast-correlator designs. The latter is showing improvement, but still some issues to resolve. During the solar observations, there have been a few small events. One M1-class flare occurred, but had almost no radio emission apparently. Activity seems to be subsiding now.

Dec 02

15:00 UT We made an attempt last night to do pointing measurements on Ant 14, but there were several problems. The tunable LO was not switching, but mainly Ant 14 was not in the subarray! After this was fixed, the wind was high, so observations were terminated early. None of the observations will be useful. We will proceed with normal solar observing.

Dec 03

12:04 UT Another attempt is underway to do pointing measurements. Early in the observations, it was discovered that the GPS clock had lost connection, which caused many subsystems to get confused. By about 01:30 UT the system had been brought back into service, and data-taking had started. Ant 12 is missing, because of a possibly spurious Lo Hard Limit in Azimuth (the current Azimuth is reading high, not low...). Also, overnight there have been many episodes of high wind, so many of the scans will be useless. Right now I count 9 potentially good scans. I also found the tunable LO saying Queue Overrun, so tuning on band14 may not have been correct for awhile--not sure when this occurred.

Dec 04

12:22 UT The wind was bad all day yesterday without let-up, hence there were virtually no good scans the entire day--maybe about 9 total. I restarted the pointing schedule last night, for a third night of attempts to get good results, and the wind was good, but this morning I found three anomalies: Ant 14 Dec drive was stuck with a permit, Ant 14 VATTN was set at 5 dB (maybe not a killer), and Ant 14 DCMATTN was 0 (definitely a killer). Also DCMAUTO was not off, which is very strange. I have no idea how these settings get corrupted. It may be that none of these data up to now are any good. The scan starting 12:39 UT may be the first with any chance.

14:30 UT The Ant 14 Dec drive spiked again, so it only successfully did one source. I have reset it, but there appears to be some generic problem with the dish that results in Dec motor-current spikes.

17:30 UT I checked again, and again the Ant 14 drive is stopped. I reset it, but I do not know if we are getting any good data. Perhaps I have to babysit it on each source change.

21:51 UT For what it is worth, the observations from 17:30 UT to now should be good, with 4 more pointings to go.

Dec 05

23:30 UT No observations at all today, because of testing of the fast correlator. The packet headers look better now, so we are getting close, but there are some issues with both number of X packets and the content of the packets, suggesting an issue with the FFT block.

Dec 06

17:20 UT Normal solar observing has started. Kjell tells me that the air conditioning stopped again, but he is cooling the room manually.

18:34 UT It seems that none of the pointing observations we attempted over the weekend are any good, even though at least some were certainly supposed to be tracking, with correct settings. As a test, I am grabbing a quick observation of 3C273--on source by 18:36 UT. Okay, I just checked, and the data on 3C273 is just fine. I cannot imagine what went wrong over the weekend. I guess we have to make another attempt to do pointing, overnight.

18:50 UT Back to solar observing.

23:41 UT Start of 24-hour pointing measurements. Ant12 "to stow". Wind 10 mph.

Dec 07

00:00 UT Continue 4-hour pointing measurements.

00:04 UT Strong wind 21 mph.

00:44 UT Front end temperatures for Ant3 and Ant14 are red.

15:12 UT The pointing measurements are continuing, and despite some losses due to wind, and again a permit error on Ant 14 Dec drive, at least now we are getting good results.

15:25 UT I updated the delay center values according to Bin's measurements on a calibrator, and the scan being taken starting now (at 15:25 UT) should have the new delays, so I can compare before and after to see if I got the sign right!

16:04 UT I checked the delay correction, and found that things got worse, but not just in the sense of getting the wrong sign. In fact, Bin has analyzed some older data taken before I made some delay changes, so his corrections are invalid. I might be able to follow the changes since then and figure out the differences, but there were at least two updates to delays in the meantime, so it sounds prone to error. I just took out the bad corrections, so we are back to the previous table (although this will not take effect until the scan starting 16:23 UT).

Dec 09

11:26 UT Natsuha is running a series of long calibrator scans (70-min on each source, using pcal.fsq, which is 10 frequencies on the Hi receiver), starting at 00:00 UT today. This morning I checked and found Ant 14 with a permit error on the Dec drive, but it just happened on the current source (1130-148). I went ahead and reset it, so data over 11:25-11:40 UT will be okay (10:30-11:25 UT is no good). There are three more scans to go.

Dec 10

00:55 UT Last night's observations went well, and Bin used the first scan to determine delay centers. I took a 10-min scan of 2136+006 just now, with the same delays as last night, and then updated the delays and will compare the next 10-min scan to make sure the sign is correct. Maria also analyzed the latest pointing measurements and I successfully used them to calculate pointing coefficients for Ant 14. I have not entered them yet, but will do so shortly.

01:10 UT Started a pointing measurement without updating Ant 14 pointing coefficients. When done, I will repeat after updating.

01:38 UT First pointing measurement is complete, and Ant 14 pointing coefficients are updated. A new pointing measurement is now underway.

02:30 UT I am repeating my experiment with toggling the PA tracking on and off on 3C84. The first scan is largely missed due to the large slew time for Ant14, but after this they should be okay, starting 02:30 UT. This is band14.

14:31 UT The observations last night went well, but on analyzing it I find that the pointing is not good. However, one way it is not good is in very different pointing when the PA of the feed is rotated 180 degrees, which is something James was asking about. I now realize that this should be balanced first, and then the pointing should be determined. I wish I had thought of that earlier!

16:50 UT Started an observation on 3C273 (band 14), with a new command to sweep the PA between -90 and 90 degrees, at a rate of 1 degree every 12 s. Unfortunately, the sweep stopped at PA = 38, at 16:56:40 UT -- some sort of glitch with reading the stateframe. I then attempted another sweep at a rate of 1 degree every 3 s, but it started doing it again at a rate of 12 s, so the command has a bug.

17:30 UT Meanwhile, I discovered that there was a C-class flare, so I went (much too late) back to the Sun.

Dec 11

04:33 UT I analyzed the earlier 3C273 data, and clearly there is a large variation in amplitude as the PA changes. I plan to get back onto 3C273 when it rises at 11:20 UT, which will give me 4 hours to mess with it before the solar observations need to begin. I want to try a faster rotation like 1 degree every 3 s. If that works, I should be able to get a measurement in 10 min, and iterate quite a few times with different X positions.

11:30 UT I had a little trouble with Ant 14 (Maths Error), but I set up for rotating the PA from -90 to 90 at the start of the file at 11:34:57 UT. Hmm, I forgot that it would take awhile to get to -90, so this is not a complete test. I have to move the PA to the start before starting the count-down, which I could do by issuing an FRM-SET-PA command first. The X-axis position is 500.

12:15 UT That worked well, actually, and I can see that we are way off in the rotation axis. I am redoing the measurement with an X-axis position of 510. I worked out that a 10 mm shift in focus position is equivalent to a pointing shift of 3'. The modulation should get worse if I went the wrong direction, or better (less modulation) is I went the right direction. This will be the file starting at 12:14:58 UT.

12:32 UT Well, that is a bit embarrassing. The modulation at X-axis 510 is almost gone! That means James had the right position after all, and I moved it in order to peak up at some point, thereby putting it out of the center! I am doing another test at 520 mm, just to verify. This will be the file starting at 12:34:58 UT.

12:52 UT That run had exactly the expected behavior, so now the best pointing is on the other side (negative PA), but not nearly as much modulation as for 500. So I have set it to 512 mm, and will do one more run, where I expect it to be exactly right! This will be the file starting at 12:54:58 UT.