[evlatests] Antennas 23 and 25 phase/amplitude jumps

[Rick Perley]

    My previous report noted the phase of antennas 23 and 25 
simultaneously jumping at X-band by 55 and 122 degrees, equally in both 
IFs A and C, with the jump occurring prior to the scan, and a return 
jump in the middle of the scan. 

    I find now that the correlation coefficients for these two antennas 
have dropped by 26 and 17 percent, (respectively) at exactly the same 
times.  The drop in coherence is not due to Tsys, which was stable 
throughout.  The drop must have been caused by some 'chatter' in the 
phase -- but if so, the timescale for this very much shorter than the 
integration period of 3.3 seconds. 

    I had also reported two similar phase jumps at L-band, for antennas 
18 and 25.  Curiously, no change in L-band correlation coefficient is 
noted for either.