[evlatests] X-Band birdies

[Rick Perley]

    With the last few minutes of Ken's software time, we tested the 
presence of the two birdies discovered a week or so ago:  8192, and 
'8797' (where the quotes mean that it is detedted near 8797, but is not 
actually due to a radiating source at that frequency).    Center 
frequencies used were 8192 and 8790 MHz. 

    Since last week, the T304s for 13A and 18A have had absorbing 
material placed within them, in the hope that this would reduce the 
problem to a more manageable level. 

    The quick results are encouraging. 

    We observed in mode 2AC, with a BW of 25 MHz, giving a (rather 
coarse) resolution of  1.56 MHz. 
   
    Auto-correlation (total power) spectra were utilized, as the fringe 
rate at X-band in B-config is pretty fast, and causes significant fringe 
winding loss on the cross-power spectra. 

    A)  8192 MHz

    The birdie is not seen on 13A, 13C, or 18A.  It is seen weakly on 
14A and 18C, and much more strongly on all the others:  14C, 16A, 16C, 
24A and 24C. 

    B)  '8797' MHz

    The birdie is absent on 13A, 14A, 16C, 18A, and 24A.  It is weakly 
seen on 14C, 16C, and 24C,  is quite strong on 13C, and is 
overwhelmingly strong on 18C. 

    We need to look more carefully with higher resolution.  Perhaps on 
Friday during the Dynamic time scheduled between 7 and 8 h, LST?