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

[Rob Long]

Ken is right, L301s either lock or they are (hard) broken. When we see 
"tuning failures", do we actually see L302 lock warnings? I can look 
into archive data and get a feeling for what the synths are doing (but I 
can not see frequency).

Rob

Ken Sowinski wrote:
> 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.
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