[evlatests] Q-band 'Failure to Tune'

[Rick Perley]

     We ran the (final!) beam holography run last night, at Q-band. Two 
separate tuning pairs, with X-band referenced pointing.

     A repeated 'failure to tune' was noted in both tuning pairs:

     Following X-band referenced pointing, antennas 15 and 18 usually 
gave no fringes on the following Q-band observation.  Fringes returned 
in all cases on the next calibration scan (with no X-band in between).
     One characteristic of this failure mode makes it different from 
that which Ken and Hichem diagnosed last week:

     In all cases, both the AC and BD IFs gave no fringes.

     As noted above this failure mode primarily affected ea15 and ea18 
-- roughly eight separate times.  Ea19 and ea20 both failed to tune one 
time only (at different times).