Intro

       Crosses were done using the 12meter sband receiver on 04-06apr22.

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Setup

The setup was:

• one freq band centered at 2278 MHz
• No cal was fired during the crosses.
• the cal is present but it is not temperature stabilized and we have not measured its value yet.
  
• 3 sources:
• 3C144 (crab)   flux=775 Jy
• 3C274 (M87)   flux=122 Jy
• 3C405 (CygnusA) flux=785 Jy
• (the fluxes were taken from chris salters p12m catalog sband values. I'm not sure what the exact sband freq was that he used.
• pointing:
• az, el strips.
• 4 deg each. 100 secs/strip,10 hz sampling
• 1000 samples/strip, .24Amin/sample. 167 samples per 40Amin fwhm beam.
• mock setup:
• 2278Mhz cfr
• 172.032 bw, 1024 channels , 166Khz/channel
  
• pola,b recorded separately

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Processing the data

• idl was used for the processing.
  
• scan for the cross files with mascrossfind()
• input the crosses with mascrossinp()
• compute a  mask  to exclude freq channels with rfi:
• compute the rms/mean by freq channel
• use spectra from the 1st 1/3 and last 1/3 of the azimuth strip
• exclude channels 3 sigma above the median rms/mean
• compute the total power using the above mask. (polA,B have been averaged)
  
• compute the az,el offset for the center of each total power sample
• fit a 2d gaussian to each cross.
• Use mascrossfit2d()
• this includes a rotation angle to align the az,el axis with the ellipse.
• It also includes a slope in the el direction (dz/del)
• The resulting parameters were used to give
• az,el pointing error
• Tsys variation from mean value (we didn't have a cal)
• sefd
• fwhm of fit (the az,el fwhm were averaged).

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Plotting the results:

    The plots show the system performance results (.ps) (.pdf)

• Each source is plotted in a different color
• Black: 3C144 .. crab
• Red   : 3C274 . . M87
• Green:3C405  .. Cygnus A
• Page 1: system performance versus elevation.
• top: Tsrc/Tsys vs elevation.
  
• M87 is about 22% of Tsys, the crab is about 16%
• 2nd: fractional change of Tsys with elevation
  
• Since we don't have a cal,  i divided all measurement by the mean Tsys.
• It was relatively stable. for each source < 10% variation.
• 3rd:  SEFD vs elevation
• 3C275 and 3C405 were both about 3600Jy
• the crab was about 4700.. If we had a cal we could tell if this was Tsys or  gain (maybe next time i'll use the cal).
• Need to check if the fluxes are correct.
• bottom: FWHM beam widths vs el
• units are arcMinutes.
• all source are very close to 40 Amin with little scatter.
• the 3 outliers were probably a measurement error.
• The crab is 9x5 amin. With a 40 amin beam. this will not affect things very much.
• Page 2: system performance versus azimuth
• same plots as above but versus azimuth.
• the Tsys variation of 3C405 at -30 deg azimuth is not seen in the Tsrc/Tsys plot
• So this is an electronic gain variation that cancels out in Tsrc/Tsys
  
• Page 3: Pointing error
• The units are arc minutes (the beam is 40 arcminutes).
• the top two frames plot az,el pointing error vs azimuth
• The bottom two frames plot az,el pointing errors vs
  

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SUMMARY:

• sband fwhm is about 40 amin
• the sefd is around 3600 Jy (except the crab is an outlier)
• the pointing error at sband is .44 Amin az, .395 Amin el.