lbw rfi from cross head
16mar10

    Data monitoring during the platform beam repair (16mar10) showed rfi coming from the lbw cross head. The setup was:

• lband wide receiver in linear pol mode
  
• mock spectrometer using 4 boxes to cover all of  lband.
• .1 second dumps, 21 Khz resolution, full stokes data taken, 8192 channels/172.032 Mhz
  
• Data was taken from  16:42 16mar10 to 07:41 17mar10 ast.
  
• The telescope was sitting at az=296.4, za=8.

Plots/images were made of the cross head rfi using the band centered at 1350 MHz. This band included some of the most regular occurences of the cross head rfi (1317, 1400). Other frequency bands in the lbw reciever also showed this rfi.

    Dynamic spectra showing cross head rfi (.gif):

• Top: polA, bottom: polB
• Each dynamic spectra shows 250 seconds of data (2250 .1 second spectra)
  
• The cross head rfi appears at:
• 1318 MHz and 1398. MHz
• PolB has a wider rfi range at 1398 than polA.
  

    The plots show the frequency of the total power variations for the rfi frequency ranges (.ps) (.pdf):

• Page 1:
• A total power time series was computed for 4 MHz  about 1400 MHz and 1317.7.
• The transform contained 2250 .1 sec time samples.
  
• The power spectrum was then computed for each of these time series:
• Top: 1400 MHz power  series spectra
• bottom: 1317.7 MHz power series spectra
• Black is polA, red id polB
• Multiples of 1.2 Hz has been flagged in green.
  
• The crosshead rfi is stronger in polA than in polB.
  
• Page 2: Average spectra (225 secs) for the data  used.
• The resonances in the lbw feed near 1400 MHz are flagged in blue (polB) and green(polA).
• These are very close to the frequency for the cross head rfi.
• 1317.7 (the center of the other cross head frequency band is also flagged).
  
• There may be a small bump in polA above this frequency. Could this also be a resonance?

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Summary:

• Rfi at 1.2 Hz is seen in the lbw receiver.
  
• The rfi was most often seen around 1317 and 1400 MHz. It was also seen in other frequencies of the receiver.
• The 1400 MHz rfi is very close to known resonances in the lbw feed.
  

processing: x101/100316/rfilbwmock.pro