[evlatests] 10-second tuning failures at X-band

[Rick Perley]

     Never, ever, does this appear in the middle of a scan.  Only at the 
beginning (95% of the time), or at the end.

On 08/31/2015 08:48 AM, Walter Brisken wrote:
>
> If it is a correlator setup issue, it probably is happening within 
> scans as well, correct?  If so, things would probably not look too bad 
> (the previous model would just be extended another 10 seconds I 
> presume), but there would be differences and this would break 
> accountability of the delay model.  Might show up best at high 
> frequencies on long baselines pointing near zenith where the second 
> derivative of the delay model is greatest.
>
> -Walter
>
>
> On Mon, 31 Aug 2015, Ken Sowinski wrote:
>
>> On Mon, 31 Aug 2015, Vivek Dhawan wrote:
>>
>>>
>>>
>>>  Sounds lke L302's failing to lock for 10 sec, a fairly common 
>>> transient
>>>  effect on 1% of the 224 units. But why it is only at X band I cannot
>>>  explain
>>>  - I assume you changed bands many times after the reference pointing?
>>
>> I don't think so; that would break two IFs at a time.  My money
>> is on the distribution of current delay and phase models and
>> sideband information within the station board.  Tracking it down
>> will probably not be easy.  For Rick: when it fails for an IF,
>> is it true that all subbands for that IF behave the same way?
>>
>> Ken
>>
>>
>>>  On Mon, August 31, 2015 08:26, Rick Perley wrote:
>>> |       The calibrator survey run, taken last October, has revealed the
>>> |  continued presence of short-lived tuning failures.  The 
>>> characteristics
>>> |  are quite simple:
>>> | |       1) No fringes at the beginning of a scan, lasting exactly 10
>>> |  seconds.  After this interval, full-valued fringes abruptly occur.
>>> |  Hence, this is not a pointing problem.
>>> | |       2) Roughly 20% of scans are affected, nearly always a single
>>> |  antenna, occasionally two.  This seems consistent with a random
>>> |  process.  There was no clear tendency for any particular antenna 
>>> to fail
>>> |  more often.
>>> | |       3) The four IFs failed independently, with equally 
>>> likelihood --
>>> |  failures are always on a single IF.
>>> | |       4) So far as I can determine, this problem only occurs at 
>>> X-band.
>>> |  (I have checked P, L, S, and C, so far).
>>> | |       5) The on-line flagging system (unsurprisingly) does not 
>>> flag these
>>> |  failures.
>>> | |       These X-band observations followed X-band referenced 
>>> pointing,
>>> |  which utilized a different tuning and correlator configuration.
>>> | |       There was also a single incidence (out of 182 scans) where 
>>> the
>>> |  *last* 10 seconds abruptly lost fringe power.
>>> | | |  _______________________________________________
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>>> |
>>>
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