[evlatests] Band-changing reliability at L-band

[Rick Perley]

    The Herc A 'demo science' run, taken Friday, required numerous band 
changes, amongst L, S, C, and X bands.  For L-band, the requested 
frequencies (center) were 1657 and 1467 MHz (AC and BD, respectively).  
In the observing script, L-band followed either X or S band.  Following 
is a summary of the 'failures to fringe' for L-band only.  For 
reference, there are 37 individual observations at this band.  With the 
exception of item 'D', none of these problems were flagged by the system. 

    A) Antennas 15, 17 and 26 gave no fringes at any time.  The first 
two have no receivers.  According to the EVLA summary sheet, ea26 was to 
have its L-band receiver installed on Dec 08. 
    B) Antennas 3 and 19 gave no fringes at any time on the AC IF.  Good 
fringes are seen in BD. 
    C) Antenna 25 only rarely provided fringes (perhaps 10% of the time) 
on the AC side.  Fringe amplitudes went from noise to good values in the 
middle of some scans.  All was fine on BD. 
    D) Antenna 12 gave no fringes for three consecutive scans in the 
middle of the run on any IF.  There is nothing in the log about that 
antenna temporarily out.  The same behavior was seen for antennas 11 and 
13, for a single (different) scan each.  All of these were properly 
flagged by the system. 
    E) Antenna 6 failed to give fringes on the AC side only for 2 
individual scans, while antenna 7 filed on the AC side once.