using lband wide to look at the rfi environment (64usec dumps)

• data taken 05mar19.
  
• telescope sitting at : az=84,za=18 .. had strong faa radar response in  22feb19 data.
• 64Usec dumps, 625 KHz rbw., 37 seconds of data (> 3  12 second radar rotations.
• link to writeup
  
• The average and peak hold spectra  in degrees Kelvin (.ps) (.pdf)
• The average and peak hold spectra in dbm (.ps) (.pdf)
• The total power vs time (.pdf)
• The radar bands total power vs time(.pdf) (6.5MBytes)
• The radar bands total power vs time (blowup around max total power) (.ps)  (.pdf)
• Plot showing the onset of compression in the if/lo or backend (.pdf)
• Not sure where in the if/lo the compression occurred.
  

Notes:

• spectra labeled peak hold, are maxima for the N spectral averages.
• The true peak value will depend  on the duty cycle of rfi  vs spectral average.
• The aerostat radar balloon was not up during these tests. It is probably the stongest signal
• The signal strength vs az,za can change by 10-20 db as we move in az and za.'
• ALPACA needs to remain linear through the digitizer and..
• The butterfly stages of the PFB should not overflow.
• The fpga's usually use fixed point 18  bit registers.
• The noise grows as the sqrt(Nadditions). so normally every 2 butterfly stages you downshift 1 bit.
• coherent signals (tones, radars) grow linearly.. so you'd need to down  shift every butterfly stage to protect from overflow.
  
• the mock spectrometer (fpga based with pfb's) has this overflow problem with the radars.
• links
• ao40 page
  
• phil's rfi page
• radar measurements, info, frequency table
• List of rfi seen at arecibo
  

home_~phil