•  winds over 100mph
  
• rainfall of  39+ inches  in 3 days.
  
• The linefeed broke off and fell into the dish
• multiple sections of the catwalk floor broke off and fell into the dish
• A lake beneath the reflector (up to 8 feet deep)  was finally drained sometime in November.
• Up to 80 panels needed to be replaced
• 2 east/west cables were broken and had to be replaced.
• the cables were approximately 150 north of ao9 and 100 feet east of north (these are ballpark numbers).
  

• 22oct17: platform tilt was checked with azimuth and the tilt sensors in the dome.
• 27oct17:1400 lbw of ballast added to end of azimuth (ch side) to compensate for loss of linefeed,
  
• 01nov17: tiedown tracking becomes functional
• 01-18nov17: data taken (with sbn) for a new pointing model.
  
• 09dec17:  commercial power returns to AO.
• feb18:  damaged panels and east-west cables repaired
  

Degradation of the telescope gain:

    The telescope gain will be affected by:

• the accuracy of the reflector surfaces
• the position of the horn relative to the focal point of the optics.
• the pointing error.
• this will normally not be a problem during calibration scans since  strips +/- 3 beam widths  in length are used for the beam fits.
• Normal tracking by observes will be affected by the pointing error.
  

Looking at the telescope gain before and after maria.

    x102 calibration from Pre and post maria were used to check the telescope gain. The calibration patterns do 4 strips through the source, each 6 beamwidths long.

• Pre maria: 01jan16 to 18sep17.
• postMaria: 01Nov17 thru 27jan18.
• frequencies/rcvrs used:
• sbn: 2380 MHz
• sbh: 3500 MHz
• cband: 5000 MHz
• xband: 9000 MHz

 The table below has the telescope gain before/ after maria  by frequency:

Each file contains two pages:

• Page 1: Gain vs azimuth angle
• Each source is plotted with a different color/symbol combination.
  
• Top frame: feed in the north half of dish (looking at southern sources)
• Bottom frame: feed in the southern part of the dish (looking at northern sources)
• For each frame the data is plotted rise to set.
  
• the left 1/2 of the plot is source rising (looking at the west 1/2 of the dish)
• the right 1/2 of the plot is source setting (looking at the east 1/2 of the dish)
• Page 2: Gain vs azimuth and za as an  arrow plot:
  
• This is an arrow plot that tries to show the gain variation vs azimuth and za
• The length of each arrow is proportional to the gain
• The top of each plot shows the K/Jy for a tick interval.
• It is not easy to compare different vector lengths (that change by a small amount).
• The angle of the vector with the top of the page is also proportional to the gain.
• The top of each page lists the gain for 0deg, 90 deg, and 180 deg rotations
  
• the range of gain for each plot varies.
  
• When looking for variations in gain, the eye can follow vector rotations better than changes in length.
  

Comparing the gain before/after maria:

   Gain vs az for common sources tracked before and after maria (.ps) (.pdf)

• black * are sources tracked before maria
• red *  are the same source tracked after maria.
• Comparing the same source before and after removes any error in the flux measurement.
• pages 1-3 show sband 2380 MHz measurements
• 20 to 30% lower after maria
• pages 4-5 cband, 5000 MHz measurements
  
• about 50% lower after maria
  
• page 6  xband 9000 MHz measurements.
• 50 to 75% lower after maria.
  

Decrease in gain rise to set

• The plots show that the gain is generally decreasing rise to set.
  
• Sources that track the southern part of the dish have a larger drop off
• This was visible before and after maria.
• This could be caused by the distance between the horn and dish changing.
• the SE fill area has had sinking  problems in the past (the main cables had to be re-tensioned).
• It could also be a problem with the positioning of the platform relative to the dish
• the 1az term was measured to be small , so there is probably not a large tilt.
  

Summary

• The telescope gain has changed before/after maria. Typical changes are:
• 2380 MHz 20-30%
• 5000 MHz 50%
• 9000 MHz 50 - 75%
• gains are decreasing rise to set, especially sources that track the southern part of the dish
• This was evident even before maria.
• the SE fill area of the dish has had problems in the past with sinking.

Todo:

• find out if the focal distance is too short or too long.
• track B1328+307 and/or  B0134+329  rise to set at cband or xband using the calibration scans.
• after each calibration scan, move the platform height. Cycle above, on , and below the expected focal height
• As a function of azimuth see how the gain changes.
• This requires functioning distomats (which we don't have).
• It also needs to be done at night, so there is sufficient tension in the tiedowns.
  

  processing: x101/171212/ see Readme file.