[evlatests] RFI Spectral Sweep

[Rick Perley]

    Ken has generated a script which surveys the entire band, from 1 to 
50 GHz, in 1 GHz-wide 'chunks', with each of these providing 250 kHz 
resolution, in both parallel-hand polarizations. 
    Besides the interesting zoo of RFI which this reveals (and which 
will be described separately), some other issues are found:

    1) The highest seven 'tunings' (from 43 through 50 GHz) have no 
data.  (This from last evening's test run).  'No Data' means just that 
-- not 'integer zeros', but absolutely nothing at all.  On the previous 
test, only the highest three tunings were empty.  And on the first test 
(two days ago), all Q-band tunings had data.  What has changed?

    2) All lower sideband tunings (all of X-band, and Ka-band from 26 
through 32 GHz) have spectra which are both mis-labeled and 
mis-ordered.  Mis-labeled means that the frequencies in the headers are 
incorrect.  Mis-ordered means that the eight subbands are incorrectly 
placed:  subbands 1 and 8 are interchanged, subbands 2 and 7 are 
interchanged, etc.  The former problem is corrected if we load in an 
alternate SDM (from /home/mctest/evla/mcaf/workspace).  The latter 
problem is not corrected by this -- but Lorant has written a special 
BDFin script which correctly re-orders these subbands upon loading into 
AIPS.   It seems to me that these new issues need to be corrected 
automatically without users having to invoke special scripts. 

    3) Subband #6, for the LCP correlation, for every single tuning, is 
bad.  The spectrum is 20 dB too high, and is composed entirely of 
noise.  RCP is fine. 

    4) And, most extraordinarily, the L-band spectrum (1 -- 2 GHz 
tuning), in both polarizations, is entirely blank!  The spectral density 
and spectral shapes are correct, but there is not a single RFI spike 
visible!  (We wish ...)  All other tests of this script gave proper 
L-band spectra.  The 'blank' spectra are on all antennas. 

    5) In the lower S-band tuning only (2 -- 3 GHz), subband 3 is 
completely corrupted in both polarizations -- the digital radio 
transmisions (which are in this subband) are weakly visible, and the 
spectral floor is 20 dB too high (like those reported in note 3, above).