[evlatests] RFI Book online

[Rick Perley]

    I've made ps images of the results of the latest 'RFI Sweep'.   The 
plots are currently residing in my FITS area \DATA\SECHELT_1/FITS with 
names:  RFIn-m, where n and m are integers, and m = n+1.  For example, 
the RFI plots for the frequency range 8 to 9 GHz are found in RFI8-9.   
These plots should eventually find their way to a more accessible 
location. 

    Each of these files contains 8 pages, each corresponding to a 128 
MHz-wide span.  The channel separation is 125 kHz.  Hanning smoothing 
has been applied to minimize Gibbs ringing.  The scale is logarithmic, 
in dB, with arbitrary offset.  The scale can be roughly calibrated by 
noting that the mean power level is roughly equal to the antenna SEFD in 
Jy.  There is no bandpass calibration, so the downturns at the edges are 
due to the analog and/or digital filters.  All plots are from the RCP 
correlation -- the LCP looks very similar. 

    Each plots is an ampscalar sum over all baselines.  Thirteen 
antennas were in the array at the time (this number was set by data 
rates through the CBE) -- not all are fully equipped at all bands, so 
the plotted averages for each band include only those antennas with 
receivers at that band.  The internal averaging was 1 second (to reduce 
phase winding -- we want to see the RFI!), and the array was in the B 
configuration. 
   
    The RFI seen in these plots is a combination of internal and 
external.  In general, the internal RFI are CW tones, and can be 
recognized as such from their very narrow width.   All internal 'tones' 
appear to be integer multiples of 128 MHz.  The spectral channels have 
been arranged so that these 128 MHz multiples always lie centered in a 
spectral cell -- due to the Hanning smoothing, these then occupy 3 
spectral cells, with the edge pair always 3dB below the center External 
signals always appear somewhat extended -- even the radars can be seen 
to have significant width at this resolution. 

    Remember that delay tracking will greatly decrease the amplitudes of 
these signals in any image -- especially at high frequencies and long 
baselines.   The amount of reduction can be anywhere from -10 to -60 dB, 
depending on circumstances.