[evlatests] Failure to tune at x-band

[Ken Sowinski]

On Sat, 16 Jan 2016, Rick Perley wrote:

>     A beam-holography script was run last night, at X-band.
>
>    Repeated 'failures to tune correctly' occurred on four instances.  Three 
> of these were after x-band referenced pointing was done.  The referenced 
> pointing was done with different frequency tunings (but in the same band). 
> The other instance was at the beginning of the observation.  For all four, 
> the failures were only in the 'A/C' IFs.  The B/D pair were fine.
>
>    Details:
>
>    1) Instance A:  First scan in the run -- antennas 5 6 18 and 19 did not 
> tune correctly (no fringes), on SPWs 1 through 8, and both polarizations.
>
>    2) Instance B:  Following the first referenced pointing. Antennas 6, 9, 
> 18, 24 and 26.  (On the following scan, all antennas except ea06 came back to 
> life.  Ea06 returned on the next scan).
>
>    3) Instance C:  Following the 2nd referenced pointing.  Antennas 3 5 11 
> and 18.
>
>    4) Instance D:  following the 3rd (and last) referenced pointing. 
> Antennas 9 11 13 19 24 26 and 27.
>
>    This failure is particularly insidious since it is *not* caught by the 
> flagging system.  In nearly all cases, the non-fringing antenna returns on 
> the following scan.
>
>    This failure mode is long-standing.  I believe I have seen it in every 
> case that I can remember where and X-band observation follows an X-band 
> referenced pointing done at a different frequency.

As Rick says this is a long standing complaint.  We should find time 
next week to exercise the the antennas as he does with a test script
and see what they are doing.