[evlatests] Notes from EVLA Test Meeting of March 25

[Dan Mertely]

Good overview of the RFI situation.  Inter-spaced below are
a few minor corrections or additions.  -Mert

Barry Clark wrote:
> EVLA Test Meeting, March 25, 2010
> 
> 1.  RFI
> 
> R. Perley reports on an oldish cross correlation spectra taken at
> L band.  Strongest signals:  1030, 1090 MHz aircraft transponders.
> Aircraft DMEs, from 1090 up to 1130 MHz.  L2 (military) GPS at
> about 1372 MHz.  

The Military GPS signal is 1227.6 +/-10 MHz.  It should be
seen most of the time as various MEO GPS satellites move
across the sky.  There is a GPS-L3 signal at 1381 MHz also,
but it is very intermittent, except for once per quarter
4-6 hour special calibration events.

1244-1372 is fairly clear, with four moderately
> strong, but narrow band, radars.  

The Russian GLONASS navagation system also has a set of
military frequencies, paired with their 1600 MHz range
channels.  Their military GLONASS channels range from
1242.9375 - 1251.6875 +/- 5 MHz.

The 1372-1500 MHz subband has
> an internally generated birdie at 1408 MHz (=11*128).  The
> 1500-1628 MHz subband is OK up to 1526, where the satellites
> (INMARSAT, GPS, GLONAS, etc) take over, with signals to 25000 Jy.
> The 1612 OH band, 1607-1617 MHz is reasonably clear.  The
> 1628-1756 MHz subband contains weather balloons (1670-1680 MHz,
> but only a couple of hours twice a day, at 12h and 0h UT), and
> meteorological satellites (1680-1710 MHz).  The 1756-1884 subband
> was fairly clear except for three signals of about 30 Jy at about
> 1800 MHz.  In the final, 1884-2012 MHz band, the upper part of
> the band is badly interfered with by PCS cell phones, 1930-1990 MHz.
> 
> He also reports on a total power scan of S band.  There is an
> allocation for balloon transmissions at 2105 MHz.  Digital Satellite
> radio is very strong signals in 2319-2347 MHz.  There are signals
> of unknown origin at 2188 and 2199 MHz.  In fact, the whole lower
> part of the band is pretty bad up to about 2490 MHz.  There are
> strong interfering signals in the upper part of the band, 3600-
> 4200 MHz, which he mainly saw at low elevations (unclear why).
> 
> M. Rupen reported on problems at the bottom of C band (4000-4500 MHz),
> which he attributes to interference.  

The spectrum from 3.6-4.2 GHz is allocated to the fixed
satellite service, which broadcasts network feeds to subscriber
local TV stations, as well as "big dish" hobbyists.  These are
fairly strong, wide-area coverage satellites in geosynchronous
orbits, so they will be low in the east and west, peaking at
90-Latitude due south.

He was observing with 2 MHz
> channels, and was seeing strong time variability and large closure
> errors, but did not see a spiky spectrum, probably due to the large
> channel width and multiplicity of signals.
>