Sections:

plots:
    the spectral output results (.ps) (.pdf)
    dynamic spectra for the narrowest band shows the drift in the rfi frequencies (.gif):
    the results of the azimuth swings (.ps) (.pdf):

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Intro

   Project A2335 (gass) reported rfi at 1360 MHz on 12aug11 thru 14aug11. The radar blanker was on when this data was taken (with the interim correlator). It was reported as narrow band with variable amplitude.

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15aug11 take data while sitting.. freq dependence

    On 15aug11 test data was taken with the mock spectrometer to learn something about the rfi. The setup was:

• azimuth=234.34, za=11 10:30 am
• lband wide using linear polarization and no filters. The radar blanker was not used.
  
• The faa radar  was only broadcasting at 1330 MHz (1350 was off).
  
• The aerostat, remy radar, and punta salinas were broadcasting.
• The spectrometer setup used 1 second averages,8192 channels,  for 523 seconds.  5 different bands were used:
• 
  

• bandwidth MHz	resolution KHz	cfr MHz
  .344	.042	1360.045
  1.72	.210	1360.050
  3.44	.420	1360.055
  28.67	3.5	1360.060
  172.032	21.0	1300.

  
  
• The center frequency differed to separate out birdies from within the mock box.
• 39, and 77 KHz biridies are generated inside the box. By changing the rf cfr, these birdies end up at different rf frequencies so they can be identified.

The plots show the spectral output results (.ps) (.pdf):

• Page 1: 523 second spectra averages:
• The data was averaged for 523 seconds and then a bandpass correction was removed.
• Top: 1359.75 to 1360.32 MHz  polA blotted for each of the 5 bands
• The colors are the different spectral resolutions
• The dashed purple lines are the common rfi that comes from outside the mock box. The other lines are being created inside the mock box.
  
• Bottom: the 42 Hz resolution band
  
• Black is polA, red is polB
• the dashed purple lines are the rfi.
• Page 2:
• Top: blowup of strongest birdied (1360.016) averaged for 512 seconds
• polA is stronger than polB
• The total width is about 1400 Hz.
• Bottom:
• overplot 10 second averages around 1360.016 birdie (polA).
• The lines have been offset for display.
• The 10 second width is about 900 Hz.

The dynamic spectra for the narrowest band shows the drift in the rfi frequencies (.gif):

• This shows the 1360.014 and 1360.065 birdies
• You can see the drift in the birdie frequency vs time
• both birdies drift together.

processing: x101/110815/rfi1360mock.pro

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16aug11: azimuth swing

    On 16aug11 two azimuth swings were taken. The setup was:

• azimuth: 265 to 630 at .35 deg/sec and then back. za=15 degrees.
• radars active: faa,1330,1350, remy:1270,1290, punta salinas mode A.
• lband wide  setup with linear polarizations.
  
• Mock spectrometer setup:
• 1 second sampling
• bandwidths:.344,1.72,3.44,28.67, and 172.032 Mhz
  
• center freq: 1360.053,1360.058,1360.063,1360.068,1300.
• a constant 1.008 Mhz was added in the digital mixer to arrive at the above band centers.
• This moved the DC spike in the center away from the rfi of interest.

The dynamic spectra shows the 1360.015 birdie vs azimuth for the CW swing (.gif)

• The median value of each swing was used for the bandpass correction.
• The drifing frequency was also seen with the telescope sitting stationary.
• The signal goes away for many azimuths.
  

processing:

• The .344 Mhz band with 42 hz resolution was used.
• The peak value about the 1360.015 Mhz birdie was recorded and then divided by an baseline average away from the rfi.
• The peak values for the  clockWise CW and CounterClockwise CCW az swings were then overplotted.
  

The plots show the results of the azimuth swings (.ps) (.pdf):

• Top: polA 1360.015 peak for CW (black) and CCW (red) swings
• 2nd: polB 1360.015 peak for CW (green) and CCW (blue) swing
• 3rd: Blowup about az=-65 showing locations of all peaks
• bottom: Blowup about az=-30 deg showign locatiosn of all peaks.
• The clockwise and counter clockwise peaks overlay each other so there is a variation of signal strenght with azimuth.
  

Conclusions:

• the 1360.015 rfi has a strong azimuth dependence
  
• The polA and polB peaks occur at differnent azimuths (this is for za=15deg):
  
• polAPk: -69.45
• polBPks:-85.78,-65.77
• The peak value gets  up to 7*Tsys in 42 Hz resolution.

processing: x101/110816/azswing1360.pro.

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Summary:

• narrow band birdies were found at:

• RFI Frequencies and steps

  Freq MHz	FreqStep (N+1)-N KHz	Comments
  1359.76855
  1359.81812	49.5605
  1359.86755	49.4385
  1359.91699	49.4385
  1360.01575	98.7549	strongest
  1360.06531	49.5605
  1360.11450	49.1943
  1360.21155	97.0459

• 
  
• Each birdie is about 900 Hz wide
• Looking at 1 second spectra, there is a peak at each edge of the 900 Hz and a dip in the middle.
  
• the birdies drift in time:
• a few hundred Hz over 500 seconds
• The spacing between the birdies is about 49.5 KHz (or a multiple of two times this).
• There is a strong azimuth dependence of the birdie strength.
• This implies that it is not coming from inside the dome.
• The azimuth values for the peaks (when dome za=15) is:
• polAPk: -69.45 deg
  
• polBPks:-85.78,-65.77 deg
  
• -65.77 polB was the strongest