[evlatests] [Fwd: Failures to Tune, at Q-band]

[Ken Sowinski]

On Mon, 28 Nov 2011, Rick Perley wrote:

>    The Wednesday evening calibration test cycled through the 8 bands,
> at a rate of one per minute.  Previous tests used the cycle:
>
>    X -> C -> S -> Ku -> K -> Q -> Ka -> L  --> X
>
>    and resulted in a high fraction of tuning failures at Ka band on B/D
> side only.  Note that this IF was tuned to 29.4 GHz, while the AC side
> was at 36.4 GHz.  The preceding band was Q, and the frequencies were
> 47.9 and 41.9 GHz on the AC and BD IFs.
>
>    For this new experiment (run Wednesday night), I perversely reversed
> the order of the tuning sequence, to see what this would do.  So, the
> order was now:
>
>    X -> L -> Ka -> Q -> K -> Ku -> S -> C -> X
>
>    For this ordering, the failures to tune are profoundly different!
> The failures now occur at Q-band, on the B/D side only.  The frequencies
> tuned were 47.9 (AC) and 41.9 (BD), while the preceding band (Ka) used
> the same pair as listed above:   36.4 GHz (AC) and 29.4 GHz (BD).
> There were 37 separate scans, and the total number of failures was 55 --
> a failure rate of (55/(26*37)) = 5.7%.  Far too high!  And none of these
> failures was flagged by the on-line system.  The failures are uniformly
> distributed over the antennas -- only two antennas showed no failures (1
> and 28), while one antenna had five (ea04) and two antennas had four (26
> and 22).
>
>    No other band showed an unusual number of tuning failures.
>
>    It would be good to end this problem.  And it would be useful if 
> these failures could at least be detected and flagged by the on-line 
> system.

When this happens it is often the case that the module has given
up and placed itself in 'standby' mode which means it will do
nothing until it gets a new command to tune to a different frquency.
I have no way of knowing whther this happens in every case, but I
use it as a diagnostic when troubleshooting non-working antennas.

There is a monitor point (obviously enough called 'standby')
to reflect this state.  It could generate an alert which would cause
flagging for the appropriate IF pair.  As a reminder:
L302-1  -> A0C0 or A1C1
L302-2  -> B0D0 or B1D1
L302-3  -> A2C2
L302-4  -> B2D2

In my experience the L301s are much less likely to fail in this way.