[evlatests] External RFI ...

[Rick Perley]

    The RFI test has shown some RFI not seen in earlier tests -- as well 
as RFI now absent which was seen before.

    'Before' means last March, when we were in B configuration.  'Now' 
means now -- D configuration.  The  spectra were formed from ampscalar 
averages over many baselines over the short observational window -- 1 
minute.  Integration times were 1 second.   Note that the use of 
ampscalar averaging very much accentuates the visibility of the RFI -- 
even short vector averages will quickly erase much of what I report below...

    I list below frequency spans with strong interference, and comment 
on changes from last March, where appropriate. 

    1000 -- 1150 MHz:  Pretty grim.  This is the zone of aeronautical 
beacons (DMEs and radars).   The lines are all narrow, with an abundance 
of 'holes'. 
    1170 -- 1260 MHz:  Extremely strong and broad emission (GPS, and 
others). 
    1260 -- 1350 MHz:  Mostly empty, with a few (~8) narrow emissions 
(radars, I think). 
    1350 -- 1525 MHz:  Mostly empty. 
    1525 -- 1610 MHz:  Zone of Death!  I doubt we'll ever be able to use 
this region. 
    1617 -- 1640 MHz:  Another deathly zone.
    1640 -- 1675:  Open
    1675 -- 1695:  Many RFI sources.
    1695 -- 1930:  Almost completely clear!
    1930 -- 1990:  Much RFI -- cellphones, I think (?)
    1990 -- 2180:  Mostly clear.
    2180 -- 2200:  Very strong RFI (geostationary satellites, I think).
    2200 -- 2310:  Mostly o.k., some strong RFI between 2225 -- 2240.
    2310 -- 2355:  Satellite radio. Completely hopeless!
    2355 -- 2500:  Mostly open, with a few (~8) narrow 'lines'.
    2500 -- 3580:  Mostly clear, but with strong RFI near:  2740, 2800 
-- 2820, 3315, 3420 -- 3460 MHz.
    3580 -- 4200:  All of this span is heavily polluted -- I think this 
is due to satellite downlinks for TV. 
    4200 -- 6110:  Almost entirely open.  *** 5990 -- 6015 had strong 
RFI in March 2010***
    6110 -- 6170:  Strong RFI throughout.  *** This span was entirely 
open in March 2011***
    6170 -- 6360:  Open.  *** 6240 -- 6270 had strong RFI in March 2011***
    6360 -- 6420:  Strong RFI throughout.  *** This was entirely open in 
March 2011***
    6612 -- 6618:  Strong RFI (which was also present in March 2011)
    6618 -- 6772:  Open.
    6772 -- 6777:   Strong RFI (also present in March 2011)
    6777 -- 7400:  Almost clear of RFI.
    7400 -- 7720:  Generally clear, but with scattered, generally 
narrow, RFI. 
    7720 -- 8000:  Clear of RFI.