[evlatests] Some RFI information

[Rick Perley]

    The recent rapid-fire observations at 26 frequencies gave us a peek 
at our local environment.  Two issues of interest (from an RFI point of 
view) ...

    1) Pulsed signals, with period 11.3 seconds, are seen at 1268.5 and 
1283.5 MHz.  These are seen equally on all baselines, so almost 
certainly have a distant origin.  These are not very strong, and easy to 
purge.  Dan Mertely is checking into the origin of these. 

    2) Continuously on signals, on some antennas only, are seen at 2944 
and 3456 MHz.  The fact that these two are separated by exactly 512 MHz, 
and are seen only on some antennas, strongly indicates an internal origin. 

    3) I observed (without thinking) a 128 MHz-wide subband centered at 
4050 MHz -- this lies squarely on the TV satellite-ground downlinks.  
But despite this, nearly all baselines show good data.  Only the 
shortest spacings show any sign of interference.  There are two reasons 
for this happy occurance ...  (1) The antennas were pointed to the NW, 
far from the geostationary belt where these satellite lurk, and (2) the 
longer spacings of C-configuration provide significant relief from the 
signals.  This bodes well for A and B configurations -- although we'll 
have to point to lower (near zero) declinations to really know.