[evlatests] RFI-free 64MHz subbands within L-band

[Rick Perley]

    The availability of a 'RSRO-style' correlator setup enables a more 
efficient L-band observing capability.  In the past, with only 128 
MHz-wide subbands available, one needed only a single IF pair -- either 
AC or BD.   Because of the copious RFI within L-band, the chances that 
all eight 128-MHz-wide subbands would contain some RFI is very high, 
leading to degraded values of the switched power, and hence degrading 
the gain calibration. 

    With 64 MHz-wide subbands now available, we have a better chance of 
placing the 16 subbands in places where more of them will be free of RFI 
for more of the time.  In addition, the doubled spectral resolution (1 
MHz rather than 2) gives better RFI editing capabilities. 

    I ran a short test today using 16 64-MHz-wide subbands, spanning 
L-band, and centered at 1500 MHz.  I observed five sources over one 
hour.  In that period of time, the SY table values for 7 of the 16 
subbands were completely clean.  Two more showed clear sign of periodic 
radar -- the pulses are easy to identify and clean up.  So at least 9 of 
the subbands look quite good.  Below is a list of the good ones. 

    1180 -- 1244 MHz
    1244 -- 1308 (has radar, easy to edit)
    1308 -- 1372 (has radar, easy to edit)
    1372 -- 1436
    1436 -- 1500
    1756 -- 1820
    1820 -- 1884
    1884 -- 1948
    1948 -- 2012