[evlatests] A few more notes on switched power issues

[Rick Perley]

    Some notes derived from further perusals of the L-band data from the 
Herc A experiment:

    As noted before, antenna 9, and L-band only, has no detectable 
switched power on any IF.  This must surely be something wrong with the 
noise diode, which acts like it's not injecting any noise at all. 

    Antenna 28, in LCP only at L-band only, has really trashy switched 
power (PDif) for part of the time.  For the 'Herc A' run, it was acting 
this way for the first 2 and last 2 hours. 

    Antennas 2 and 23, in IFs B and D only, gave zero (noise only) PDif 
for a short (ten minutes or so) period of time.  These times were 
different for each of these antennas.   For antenna 23 only, part of 
this 'blank' period coincided with no fringes being observed. 
   
    Antenna 12, on IF B only, *at all bands* is giving oscillating 
values of PDif and PSum. 

    Some antennas give very good, crisp values of PDif and PSum at 
L-band, while others provide much poorer values.   It is not clear to me 
at this time whether this is a sensitivity issue (high Tsys), or a 
too-low value of the noise diode, or some failure in the switched power 
mechanism.  We have much to learn here yet.