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Intro

   We received the xband waveguide transition to help diagnose problems with the feed/lna's. Prior to this debugging
i  reran the xband monitoring of the receiver to see what problems still existed (last runs were 01/21 jul21.

    On 19sep21 the xband receiver was monitored for 12hours. The setup was

• data taken: 19sep21  19:01 to 20sep21  07:30 AST
• telescope sitting at Az=1  el=75.
  
• xband receiver using 8050 to 9200 MHz
• Mock spectrometer used to record the data.
• 7 172 MHz bands centered at:
  
• 8132,8296,8460,8624,8788,8952,9116
• Each band spaced by 164 MHz
• 2 pols, 4096 channels/pol, 42 KHz channel width
• spectra dumped once a second
• The temperature sensor in the pedestal was online during these measurements.
• --> There had been some rain prior to the start. My hope was that it would clear up..
• It didn't, we had rain, and lightning through much of the night
• So the plots give you an idea of what rain looks like.
  

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Processing the data

• When computing the total power, frequency channels with rfi were rejected:
• compute rms/mean for each freq channels.
  
• do a linear fit to the rms vs freq and reject any channels with fit residuals > 3 sigma.
• the rfi rejection was not very helpful. We had  19 hours of data with the mean value varying with temp. The rms/chan was large so clipping at 3 sigma left a lot of rfi.
  
• the total power for each 1 second spectra was then computed over the good channels (scaling by the channels used).
• The first and last bands were only partially filled with rf power. They were cutoff by the p12m rf bandpass filter. In these cases only the part of the band with power was used for the computation.
• The total power vs time for each frequency band was normalized  to the average of the first 1000 points taken (so the units become Tsys).
  

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Total power vs time, temp

    The total power vs time  for the entire 17 hour session was plotted:

The total power vs hour of day with temp (.ps)    (.pdf)

• The x axis is hours since the start of 19sep21 (so hr 30 is 6am 20sep21)
  
• Top
• over plot total power vs hour of day for the  7 polA bands
• the jumps at 24.5 and 25.5 were when heavy rain started. The drop off after the onset shows how long the clouds/rain can affect the signal.
• You see some wandering around with the different freq bands.
  
• Middle:
  
• over plot total power vs hour of day for the  7 polB bands.
• You don't see the variation with freq as in polA
• Bottom:
  
• temperature (in the 12 meter pedestal) vs hour of day.
• Looks like the room temperature is staying well above the outside air temp.
  
• when the rain started you don't see any sudden jumps in the pedestal temperature.

The second plot shows the Tsys vs pedestal temperature (.ps) (.pdf)

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blowup total power vs time

    total power vs time blowup (.pdf)

•  The total power vs time is plotted in 1 hour blocks.
• polA 1st and 3rd frames
• polB 2nd and 4th frames.
• The  7 bands for each pol are over plotted.
• Each 1 hour plot is normalized to unity.
• There is  some variation in the 7 freq bands for polA around 28 hours.
• You do see a variation in amplitude in amplitude for both polA and polB  after the large Tsys change when the rain started. This is probably just an electronic gain variation in the 7 bands.
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Summary:

• large  variation of Tsys with rain.
• after the rain started, it took many hours for tsys to come back to pre rain values. I thought at first this might be water sitting on the dish. Felix pointed out that it is probably water sitting inside the ring that holds that capton  on the  front of the horn.
  
• With the rain, it was hard to distinguish gain jumps from Tsys change from rain.
  
• PolA
  
• showed some freq variation of amplitude.
  
• Pol B
• did not show the amplitude variation with freq (excluding the large downpour periods).
  

processing: x101/210919/xbmontp.pro