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

[Bryan Butler]

i had it in my head that we never know if the L302 fails to tune.  at 
least not generally.  for instance, if it locks on the wrong tooth of 
the comb, we never know.  i can't say anything about the L301 - nothing 
is sticking in my RAM on that one.

	-bryan


Rob Long wrote, On 11/28/11 16:34 PM:
> 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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