Projects a2703 and a2708 ran 20,21 apr14 18:00 to 1:30 22apr14. They reported trouble with their baselines.  I looked at the data from 21apr14.

The on/off data taken

Setup:

• lband wide 1350-1400 MHz range
• a2703 used 1370 hipass with the 1230-1470 filter
• a2808 used the 1320 hipass filter
• liner polarization
• interim correlator
• sbc1  12.5 MHz, 2048 chan polA
• sbc2   12.5 MHz 2048 chan polB
• sbc3   25 MHz polA,B wide band to look at rfi
• sbc4   25 MHz polA,B  to look at rfi
• 1 second dumps
• patterns
• 300sec on,off positions switching multiple times per source . (a few 240 second on/off 's were done).

The data:

•  I processed all of the data for both experiments using pfcorposonoff()..
• The data was scaled to Tsys  rather than degK or Jy.
  
• 1Tsys is about 3 Jy (30K/10K/Jy)
• The multiple on/offs on the same source were averaged together (i did not scale by the za, gain).
• After averaging, i measured the rms across the  spectrum.
• I also computed the expected rms using:
• expRms = 1.02*sqrt(2)/(bw/nchans  *1.208*2.25 * secondsOn)
• the factors are:
• 1.02 is from 9 level sampling
• sqrt(2) dividing on/off
• 1.208 from the sinx/x filters of the autocorrelator
  
• 2.25 from hanning smoothing
  

The a2703 on/offs (.ps) (.pdf)

• this data was taken 18:00 to 20:30 ast
  
• PolA is black, polB  is read
• Page 1:frame 1,2: srce 108103
• the ripple looks a more like two then 1 MHz
• large offset polA,polB.. maybe the cal got messed up?
• Page 1: frame2,3 src 108143
• looks like a detection. measured rms is about 30% > then expected
• Page 2 frame 1,2 src 108144
• Page 2 frame 3,4 : src 110007

The a2808 on/offs (.ps) (.pdf):

• data was taken 20:30 to 1:30 (22apr14) ast
• page 1:
  
• src: J0959+0503.. rfi at 1344
• J1104+3141 .. airport radar at 1351..
• Page 2:
  
• src J1210+3157
• src  J1330+3119 
• Page 3:
• src J1342+1`844
• detection
• polA ,polB +/-  .004Tsys.. is this the cals?
• src J1356+2515
• Page 4:
• src J1357+1704
• detection..
• src PG1049-006
• detection
• polA,polB again have  +/0 .004 Tsys..

What was the platform doing during the observation:

    I looked at:

• the platform height (using the distomats.. when the worked)
• the tiedown position and tensions
• the temperature (measured via the old temp sensor and the newer weather station temperature sensor)
• The rainfall (from the weather station)

The plots show the platform motions (.ps) (.pdf)

• Page 1: 0 to 24 hours 21 apr14.
• The dashed vertical lines show were a2703 and 2808 started
• Top: air temperature vs hour of day
• black: from old temperature sensor
  
• red: temperature from the weather station. (only started at 15:00)
• They differ between 15 and 19 hours, and then they come together.
• I think the old temperature sensor is shielded from the sun,rain. i'm not sure about the weather station.
• The dip at 15:00 was the beginning of a rain storm
• 2nd frame: Rain intensity (inches/hour) computed as a 5 minute running average.
  
• it was raining at .5 inches/hour 15:00 to about 17:00
• 3rd frame: cumulative rainfall (inches) for the day.
• It rained about 1.4 inches.
• 4th frame: how far the platform was out of focus (cm)
• This is the vertical offset of the platform from the correct height (1256.22feet)
• the feed is out of focus by this value * cos(za)
• the distomat readings were not working 20:00 to about 23:00.
• bottom: average tiedown jack position (inches)
• the tiedowns were turned off 15:00 to 20:00
• they were moved manually at 20:00 and then left off.
• the a2703,a2808 observers requested the tiedowns to be turned off so there would not be any adjustments between the on and the offs.
• Page 2: blowup showing a2703 , a2808 run 18:00 to 24:00
• Top: air temp vs hour of day:
• the temperature was changing 18: till about 20:00
• 2nd: how var the platform was  out of focus.
• it moved from 4.5 to around 3cm during a2703 run..
  
• there is not measurements during the a2808
• bottom: tiedown motion
• the tiedowns were pulled down 2.5 inches at 20:18
  
• This would move the platform down 2.5*/1.7*2.54=3.7 cm  (1.7 tdinch/platform inch)
  
• this should have put the platform pretty close to focus for a2808.

summary

• rain 15:00 to 17:00 cooled off the main cables, shortening them, bringing the platform about 5cm out of focus
• with the tiedowns off, the platform drifted lower about 1.5 cm in 3 hours as the air warmed up and the cables came back to the air temperature.
• The observers requested the tiedowns off, so there would be no motion between the on and off positions
• unfortunately with the tiedowns off, there was no way to stop the normal motion of the platform with temperature.
• The observer commented that it wasn't raining during the observation. The data shows that recovering from a rain storm may take hours for the cables and air temperature to come to a stable value that doesn't require active tiedowns.
• My guess is that leaving the tiedowns active would have done a better job for the position switching
• In the past, when the distomats failed, the telescope would switch to use a temperature sensor to control the height (using a model).
• This model was never very accurate because the air temperature (which was used as input) and the cable temperatures (which you need to control the height) could vary by 5 to 10 degF.
• I've disabled this feature. When the distomat's fail, the tiedowns just stay where they are..
• If the distomats are working the program will move the platform every 2 minutes as long as the platform has moved by 1 mm
  
• this is about 1.7 degrees of phase on the standing wave. As i recall this should not give a very large standingwave.
• the observers evaluation of the data for 20,21 apr14 was:
•  In summary,  I have been observing 7.5 hours each of the last two nights (A2703+A2808), and the data are all unusable
• Looking at the on/offs  the actual rm is off by 10 to30 %.. in some cases a factor of 2.
• I'd say that they weren't perfect, but completely unusable may be pushing it a bit...
• For best baselines and if you're going to leave the tiedowns off, the platform should be thermally stable. This probably always happens by 21:00.