09mar11: 327 Mhz birdies and their Azimuth dependence

• CW swing (300 to 352 Mhz)(.gif)
  
• CW swing Blowup (300 to 327Mhz) (.gif)
  
• CCW swing (300 to 352Mhz)(.gif)
• CCW swing Blowup (300 to 327Mhz)  (.gif)

Sections:
Intro
Processing the data
Dynamic spectra of the azimuth swings
Average/PeakHold spectra for each az swing:
The azimuth dependence of the birdies
birdies with common az dependence
Summary
other: azswings done 28oct05 

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Introduction (top)

• The azimuth was moved between -90 and 270 degrees at .35 degrees/second. This was done 2 times (clockwise CW and then counterclockwise CCW). A single swing took 1100 seconds.
• The 327Mhz rcvr (cooled) with the 302 to 352 Mhz filter was used.
• The mock spectrometer sampled a 57 Mhz band centered at 327 Mhz with 8192 channels. The spectra were integrated for a  second.
• The alfa motor controller and the dome cameras were turned off.
• This is a repeat of the data taken 28oct05 (which used the interim correlator and the 30 Mhz filter)
  

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Processing the data: (top)

• For each azimuth swing a bandpass was constructed from the 1029 spectra. A fit to a bandpass was needed rather than an average since some rfi are constant and would remain in the bandpass average. The bandpass was created by:
• Compute a median bandpass from the 1029 spectra.
  
• Fit a 20th order harmonic and a linear polynomial to this median bandpass using robfit_polyfft(). This iterates the fit throwing out outliers.
• Divide each of the 1029 spectra by this fitted bandpass. This should remove most of the IF bandpass.
• For each spectra compute the median total power and subtract it. This should remove the source contribution.
• PolA and polB were averaged.

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Dynamic spectra of the azimuth swings:  (top)

• Clockwise swing:
• CWswing (300 to 352 Mhz)(.gif)
  
• CW swing Blowup (300 to 327Mhz) (.gif)
  
• Counter clockwise swing:
  
• CCW swing (300 to 352Mhz)(.gif)
• CCW swing Blowup (300 to 327Mhz) (.gif)
• There are a number of frequencies that are time variable and come and go together. They all have modulation on them. The strongest of these are:
• 308.7, 309.9, 311.07, 313.1. 314.3, 317.5, 318.9.
• Some other signals that are modulated and tend to be there all the time are: 312.31, 320 , 321.9 Mhz being the most prominent.
• The radio was tuned into the IF signal and the following radio stations were heard (in the IF):
• 312.31 is the 3rd harmonic of 104.1 (FM).
• 321.9 is the 3rd harmonic of 107.3 (FM). This is the strongest fm station.
• 317.5 was heard to be 107.3 (FM). This may mean that the other birdies (308.7,309.9.. ) are also intermods of 107.3 since they turn on and off with 317.5 .
• The large narrow spikes (327 Mhz 30*Tsys and 317.4 20*Tsys) only lasted for a few seconds. The spikes that are broader (and show the modulation ) were there more often.
• You can see a number of weak combs in the image. They will appear stronger when the channel width is narrowed (since they tend to be narrow).

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Average/Peak spectra for each az swing:  (top)

the average and peak hold spectra for the az swings (.ps) (.pdf):

• Top avg.: The average spectra for each swing. The largest birdie is at 306.98 (22*tsys)
  
• 307.00 (22*Tsys)
• 313.51    (2.*Tsys)
• 338.30 (3.0 Tsys)
• 2nd avg.: This blows up the vertical scale on the top plot
• 3rd Pk hold: This has a peak hold for each az swing (take the largest value in each freq channel from the 1029 spectra). The largest values are:
• 307.00 (600*Tsys)
  
• 309.90 (19*Tsys)
  
• 338.30 (65*Tsys)
• 4th Pk hold blowup: The vertical scale on the 3rd plot is blown up.

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The azimuth dependence of the birdies:  (top)

    The plots show the birdie power versus azimith for the 60 strongest birdies (.ps) (.pdf):

• many of the birdies are changing together with azimuth.
• Some birdies with little az dependence may be in the dome:
• 16: 313.51,
• 25:319.46
• 33:327.00
• 59:350.39
• ind 58 (350.00 Mhz) is coming from the interim correlator in the control room
• ind53:346.53 has similar az dependence as 350.00.. it may be coming from the same spot.
  

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The the birdies that have a common azimuth dependence.:  (top)

• Blowup: Clockwise swing (.gif) 
• Blowup: Counter clockwise swing (.gif)
• The 3rd harmonics of the 4 strongest radio stations are flagged with a solid vertical line:
• 102.9*3=308.7,
  
• 104.1*3=312.3,
• 106.5*3=319.5,
  
• 107.3*3=321.9 Mhz
• many of the birdies show azimuth (time) variation that matches the 308.7 (the 3rd harmonic of 102.9).
  
• dashed vertical lines centered on 308.7 (102.9*) and spaced by 1.2 Mhz fall on many of the signals.
• 1.2 Mhz is:
• 1.2= 3*.4 (the FM station spacing.
• 1.2= 104.1 - 102.9 (radio Rendor - HQ fm stations)
• These 2 station transmitters  are located in utuado within a few hundred feet of one another.
• The birdies at 314.5 and 314.5+1.2 do not line up in frequency with the comb from 308.7 although they show the same azimuth (time) dependence.
  

    The plots show the azimuth dependence:

• The 11 birdies that show a FM station dependence (.ps) (.pdf).
•  Page 1 Clockwise spin:
•  top: Each color is a separate rfi vs azimuth.
• Bottom:  Different rfi's vs azimuth has been plotted with offsets for dispay
  
• Page 2: same plots for the CCW azswing.
• Page 3-5: plot each of these frequencies separately.
  
• Group then so that rfi with similar azimuth dependence is close together.
•  The black trace is the CW swing, the red trace is the CCW swing.
  
• The table below summarizes the values.

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Summary:  (top)

• The third harmonics of some FM stations are seen in the band (see table below)
• Back in 2005 a filter was put in front of the receiver and the 3rd harmonics were still seen. This implies that the harmonics are being created outside of the receiver.
• A large number of intermods (11 to 15) are also related to the fm stations (see table below).
• There are some narrow constant birdies that may be coming from the az,el encoders. Need to test turning encoders on and off while monitoring the band.
  
• The table below summarizes the info on various birdies.

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