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Intro

   The  xband receiver on the p12m telescope was monitored for 14 hours on 30apr21. The setup was:

•  17:02:31 30apr21 to 07:31 01may21  AST
• telescope sitting at Az=0  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, 8192 channels/pol, 21Khz channel width
• spectra dumped once a second

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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 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 by the median value (so the units become Tsys).
  

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Total power vs time, temp, and ra

    The total power vs time  for the entire 14 hour session was plotted:

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

• The x axis is hours since the start of 30apr21 (so hr 30 is 6am 01may21)
  
• Top
• over plot total power vs hour of day for the  7 polA bands
• Middle:
  
• over plot total power vs hour of day for the  7 polB bands.
• The higher freq polB bands are unstable until close to midnight.
  
•  Bottom: pedestal temperature
• The pedestal temperature (behind the postamp chassis) was recorded once a minute.

Total power vs temperature (.ps) (.pdf)

• Top: median (over the 7 freq bands)  total power vs hour of day  using polA.
• The red curve is the temperature over plotted on the curve (scaled to fit)
• Bottom: linear fit total power vs temp.
• Black: total power vs temp
• red: linear fit  to total power vs temp
• The coef:
• tp=2.37 - .01724*tempF
• The total power units are  Tsys.
• So the electronic gain must be changing by 1.7% per deg F

Total power vs Right Ascension (.ps)  (.pdf)

• Top: PolA total power vs  ra
• Bottom: polB total power  vs  ra
• the dashed red line is the galactic plane.

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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.
• some jumps
• I've excluded the polB drifting. this lasted for hours.
  
• 17.45 to 17.6 8460 MHz.
  
• polA jumped up 4% for 10 minutes and then came back down.
• polB did not change.
  
• 19.2 polA jump by .3%
• 30.95 polA jumps down about .3%

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Spectra of the total power

    spectra of total power (.ps) (.pdf)

•  the magnitude of the total power spectra was computed for each band for the entire 14 hours
• spc=abs(fft(tp - mean(tp))
• The data was plotted on a log, log scale
• top: polA
• bottom:polB
• the slope of the log , log plot is a little less that -1 (about .84).
  
• So the noise is close to 1/f noise.

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Summary:

• The electronic gain dependence with temperature :
• -1.74 % per deg F change
• Pol B drifted by up to 3% over 7 hours. Pol A did not show this drift
• The amplitude of the drift was a function of the band frequency. Higher freq drifted more.
  
• PolA Did have some sharp steps of about .3%
  

processing: x101/210430/xbmontpslow.pro