Intro

180617 No correlation using xband receiver.

Receiver temperature:

•  PolB of the xband receiver has been reporting system temperatures in the 1000's of degrees since early jun18
• either the pol is dead, or the cal is not working
• If the correlation used polB, they should try with just polA

Pointing/focus:

• Page 1 az,za position, encoder error.
• top frame: azimuth position vs hour of day (ast).
• 2nd frame: za position vs hour of day
• looks like the source came into the beam (19.69 deg za) around 9.4 (09:24)
• they sawtooth motion was probably moving between the source and the calibrator.
• 3rd frame: encoder error vs hour of day
• black is the  azimuth error, red is the za error.
• The vertical scale is +/-7200 arcseconds (+/- 2 degrees)
• bottom frame. A blowup of the encoder error.
• the vertical scale is +/- 30 asecs.
• the fwhm beam width at 9000 MHz is about 35 asecs.
• Both the black and red line need to be within about +/-6  asecs..
• This is only happening for the very last part of each look at the source or calibrator.
• The schedule is switching between the calibrator and source and arecibo does not have enough time to get on source before they move again.
• this is why there are messages in the log file saying slewing while in track mode.
• This can only be fixed by using the 12meter as the phase calibrator.
• Page 2: the tiedowns and platform height
• the source and calibrator had declinations of 26.5 and 27deg
• Top frame: The tiedown positions vs hour of day
• the tiedowns were not being used to keep the platform at the focal height (probably because there was no tension in one of the tiedowns.
• at 9.9  hours, the tiedowns were pulled down by about .8 inches (probably to try and get more tension in td 8.
• middle frame: tiedown tensions vs hour of day
• each td has two cables (a,b) that put tension on the platform.
  
• td 8 did not have any tension until around 10:00 am.
• when the source came into  the beam, the dome was at a high za, and pointing at td8. This caused the td cables to go slack
• The dome weighs too much. This is made worse as the external temperature increases (the main cables stretch more).
  
• When a tiedown goes slack, the platform will tilt. This causes an added pointing error
• more info at: http://www.naic.edu/~phil/pnt/platMotion/pntErrVsPlatMotion.html
• bottom frame: Average platform height during the run
• The green line is the height where the optics should focus
• the red lines are +/- 1 lambda from the focus
• the black line shows the average platform height (as measured by the distomats)
• The platform was more than 1 lambda out of focus for the entire run.
• a 1 lambda focus error is a 3db gain loss.
• The tilting of the platform (causing a pointing error) makes the signal decrease a lot faster than the focus err

The telescope gain at xband:

• This will cross the south part of the dish at high za.
• The southern part of the dish has had a lower gain then the other parts (especially after hurricane maria.
  
• more info at:
  
• 27Feb18   telescope gain variations before/after hurricane maria.

Summary:

• NRAO did not get any correlation on the 17jun18 arecibo data
• PolB of the xband receiver was bad  (or the cal was not working) during the experiment.
• The experiment was switching between the source  and calibrator faster than arecibo could follow.
• very little time was spent on source or calibrator.
• There was no tension in td 8 till 10:00 ast . This would have caused a pointing error (not sure how big since laser rangers didn't get any readings.)
• probably large enough to not see the source since the fwhm beam of xband is around 35 asecs.
• The tiedowns got tension back around 10:00
• With tension the platform was still out of focus by over 1 lamba (it was still too low).
• this would have further decreased the signal strength.
• the southern part of the dish has a lower gain than the northern part. After hurricane maria, this got worse.