2016 November

Nov 04

19:18 UT Reboot ROACHes to clear fault light and test whether large delays are still present. They were power-cycled and reloaded.

19:24 UT Started roachcal.scd to take packet capture data for checking delays. Still bad!

Nov 05

03:41 UT Found a potential problem in DELAYCAL_END.ctl, so took another two sets of roachcal.scd data. Still bad!

04:14 UT Started roachcal.scd for another set of data. After studying schedule.py, another problem was found. DELAYCAL_END command has to have CIEL-2 as second value on the line, otherwise source id is set to None! Yay! It finally worked!

Nov 09

01:08 UT Set up the schedule to do a long run on 3C84 with the low-frequency receiver, using pcal_lo.fsq (all bands 2.5-6 GHz). One major change is that the PA can be set, so I set it for -30. I would predict that the chi-dependence will shift by 30 degrees (the phase jump will occur at a different hour angle), but the non-intersecting axes issue will cause the same symmetric phase rotation (it depends on elevation only).

04:20 UT 3C84 schedule begins.

12:00 UT 3C84 schedule ends.

Nov 10

03:00 UT Note, the above observations showed no coherence, for reasons unknown. The receiver will be checked for pointing and focus using a total power source. I attempted to observe the Moon at the current time, but it happens to be at -6 Declination, so it is in the geosynchronous satellite belt and could not be peaked up in total power. I will observe Cyg A when it rises at ~ 21:20 UT today.

22:00 UT Began some Cyg A drift scans. Original Z offset was 200, and I could not see any increment on Cyg A, but changing to 50 gave a clear response.

22:20 UT Nominal peak of a drift scan (well seen on baseline 11-14) is 22:20 UT, but it actually occurred at 22:19:55 UT, so original RA offset is right: 0.15 degrees. Also did a Dec drift scan that peaks at 22:46:00 UT, which verifies the DEC offset is also right: 1.03 degrees.

22:49 UT Did a focus scan. This is the time when the focus was best, which corresponds to a focus (Z-axis) setting of 30 on the Lo receiver. Higher settings were significantly worse, so that by a Z-axis setting of 200 the amplitude is going to zero. This explains the lack of phase coherence on the 3C84 run of yesterday.

Nov 13

05:42 UT Attempting to see the Moon with 27-m Hi receiver. I could see nothing at nominal position, but then I got a whopping signal at about 2 degrees RA offset. This might reflect a very wrong X axis position.

05:54 UT Moved X axis setting to 500, and I do get a very high increment at nominal pointing. Best LO Receiver settings X-axis 100, Z-axis 30; Best HI Receiver settings X-axis 500 Y-axis 0.

06:25 UT Began 3C84 observations using HI receiver, with starburst_hi.fsq sequence. Given the much higher signal strength on the Moon, the sensitivity should be very good on 3C84.

Fig. 1: First fringes on Hi-frequency receiver, on 3C84.

06:35 UT Decided to switch to pcal.fsq sequence. This should provide better SNR. Yes! The data look very nice, see Fig. 1 at right.

14:25 UT Going to 3C273, for some PA tests. Oops--used the wrong frequency sequence--was pcal_lo.fsq

14:31 UT Now setting to pcal.fsq

14:37 UT Moved PA position to -35 degrees, which is the current parallactic angle (I will test this and +35 to check the sign).

14:42 UT Began move to PA +35 degrees. I should see a dramatic change in XX and YY amplitudes when feeds are parallel.

15:06 UT Went to PA +29 degrees. Looking at the data, it appears that we need to apply -chi to the PA axis to make the feeds parallel.

Fig. 2: Comparison of amplitudes on XX, YY, XY, YX (columns) for each baseline with ant 14 (rows), as PA is changed (see upper left panel). The key is that XY and YX amplitude drops for antennas 1-5 and 12, when PA = -chi, while XX and YY increase.

15:30 UT Went to PA +23 degrees (tracking chi variation). I did some analysis that verifies -chi is the correct term to apply. See Fig. 2.

15:48 UT Went to PA +15 degrees (a bit ahead of correct -chi, which is +18 at this moment).

16:10 UT Went to PA +10 degrees.

17:51 UT Went to PA -20 degrees. Obviously a lot of rotation between these two...