Intro

    On 10dec21 we took 4 scans  each with 60 seconds of data. The scans pointed at azimuths of: 180,270,0, and  90 deg (South,west,north, and east). The 15 db pads were still installed at the inputs to the sband rf box in the pedestal. We want to install a new rf  bandpass filter to get rid of the strong rfi, so we needed plots of the strength and location of the current rfi.

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Setup:

    The 12meter sat a a particular azimuth (180,270,0,90) for each scan. The elevation was set to 45 degrees.

• At each scan we took 2 x 172 MHz bands of data.
  
• The band centers were : 2260 and 2340 MHz
• We moved the centers so Dc (center of the band) was not close to the rfi.
• the current rf filter in the 12meter sband rf goes from 2185 to 2364 MHz
• Power levels used:
  

• udc attn: 15 15 db
• if2 attn : 0 0
• if2mp gave -42 -46 dbm.
  
• The 2 mock spectrometers used were set to 172MHz bw,  .1 second dumps, 8192, channels, an a/d rms of 60 counts.
  
• 60 seconds of data was taken at each azimuth direction.

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Processing the data

• The file for each scan was input (as a double), and the 600*.1 sec spectra were averaged.
• Normalizing the spectra to average Tsys (outside of the rfi)
• A mask was setup to exclude the large rfi and then he median value was then computed for these regions.
  
• The median values were then used to scale the specdtra so that Tsys=1.
• The spectra were then changed to db's (above Tsys)
  

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Looking at the data:

    The plots shows the sband spectra (.ps) (.pdf)

• The spectra had the 15db pad installed before the rf box in the pedestal.
  
• Top plot: 60 second average spectra PolA
• Bottom plot: 60 seconds average spectra PolB
• The colors are the azimuth direction for each 60 sec spectra.
• There are 2 spectral bandpasses for each direction  (with some overlap)
• The vertical scale is db above the average Tsys (taken in the rfi clean region).
• Page 1 full band
  
• The dashed line at 2370 shows where the current rf bandpass filter starts to fall off.
• The rfi at 2320 MHz in leftmost spectra is an IQ image of the rfi at 2200 MHz.
• Page 2 blowup around 2350 rfi

Summary

• The sband spectra show where the large rfi signals are in the sband portion of the 12meter receiver.
• The peak rfi  at 2350MHz is about 44db above the Tsys value.
  

processing: x101/211210/sb_rfi.pro