Intro

    A4002 has been taking 3GHz data on the 12meter using the 3180-3340 wb4 filter. This page looks at some of the rfi seen 01jul23-09jul23. Data was taken on 1,2,3,4,5,7,8, and 9 of jul23.

Notes:

• 14jul23: The cameras at the 12m were found to cause a comb of narrow band rfi (more info)
• They were turned off on14jul23
  

Other pages with related info:

•  06jun23: az swings
  

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Setup:

• The 12meter receiver used the wb4  filter (3180-3340 MHz.
• 6 mock spectrometer were used:
• band cfr: 3257.7,3329.3,3340.0,3219.3,3242.4,3320.8000 MHz
• 8192 chan/band, 24.576 MHz bw -> 3Khz channel width
• 1 second spectral integrations.
• the 6 freq bands covered 2 contiguous bands (with overlap)
• low contiguous band:3207 to 3270 MHz
• high contiguous band: 3308.5 to 3352 MHz
  
• 10sec cal on/off was followed by a 300 second on.
  

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Processing the data

• I only used the 300 second scans for the test
• there were 498 300 scans used.
  
• for each 300 sec scan i computed the  rms/mean by freq channel for each of the 6 bands.
• 
  
• an idl save file for each day saved this data (brmsAr for the day and sumI2(summary info).
  
• x101/230709/a4002rfi.pro used to input data and generate save files.
• To make the rms/mean images for 1-9 jul
• split the freq range into the 2 contiguous blocks:
  
• low freq  block: 3207-3270
• hi freq block: 3308.5 to 3352MHz
• for each 300 second rms/mean
  
• split into the 2 freq blocks
• for each freq block interpolate the  3 overlapping bands to a contiguous  rms spectra of 3Khz channel width
• do this for polA and polB
  

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Looking at the data:

    The first plots show the rms/mean by freq chan for 01jul23

•  PolA  .jpg
•  PolB  .jpg
• each 300 sec rms/mean has been plotted with an offset for display purposes.
• Since i've added a display offset, it is hard to see small rfi signals.
  
• Green lines: DC spike at the center of each mock band
• red lines (at bottom): comb from the cameras
• 3218.691 + n*15.625 MHz n=0..8
• freqs:3218.691,3234.315,3249.940,3265.565,3281.190,3296.815,3312.440,3328.065,3343.690
• drifting rfi:
• PolA:3244MHz, 3258MHz, 3338MHz
• PolB: 3313MHz, 3338MHz, 3317MHz, 3336MHz

    the 2nd set has images of rms/mean for all of the 1-9 jul23 data (after interpolating to a single spectra)

• this image is a lot more sensitive than the 01jul23 picture
• each image has been divided by the median spectra (so constant things are removed).
• the lut has been scale using histogram equlization. The max is probably  a few sigmas.
  
• The top frame is polA
• the bottom frame is polB
• The y axis is the 498 300 sec rms/means
• the bottom in 01jul23
• the top is 09jul23
  
• Low freq Block: 3207 to 3270 MHz .jpeg
• green lines: comb at 3224.84 with 15.675 spacing
• red lines: comb ath 3238.99 with 15.675 MHz spacing
  
• Hi freq block: 3308.5 to 3352 MHz  .jpeg
• green lines: comb at 3308.75 with 15.675 MHz spacing
• red lines : comb at 3319.30 with 15.675 MHz spacing
• yellow lines: comb at 3314.25 with 15.675 MHz spacing
• there are other combs that have similar spacing that hit different freq.
• The DC spike in the center of the  band does not show up because we've flatten the images by dividing by the median rms spectra.
  

Summary

• a4002  data 1-9jul23 with 3khz channel with was inspected for rfi
• the rms/mean by freq channel for each 300 sec scan was used.
• the  01jul23 image shows some drifting periodic rfi
• the 1-9jul23 images show combs with spacings around 15.675 MHz throughout the 9 days.
• these combs drift during a day, and start at different frequencies on different days.
• The combs must be intermod products
  
• The wb4 filter is narrow (3180 to 3340) MHz with no large rfi within its range
• So the intermods (if created in our system) must be happening in the lna.
• the 2 rfi's creating the comb should differ by 15.625 Mhz (if we are seeing 2F2-F1 )
  
• It would be intersting to look at these combs with the wb3 filter that covers 2750 to 3450.
  

processing: x101/230709/a4002rfi.pro,plotrfi.pro, rmsimg.pro