[evlatests] RFI Book online

[Michael Rupen]

For short-term access I've put a copy of this e-mail and all the plots (with 
.ps added; also .pdf and .gif versions) on my Web site, at

     http://www.aoc.nrao.edu/~mrupen/EVLA_RFI/

The gifs come out as movies so they're not so useful, but hopefully you
can access the PDFs easily enough.

I'll upgrade this website a bit (add an index.html so you can find things
more easily) over the next day or two. If these are used much we should
of course move all this to the real RFI pages -- that would be easy to 
automate.  I'll check in with Dan on that, today or tomorrow.

                  Michael


>    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.
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