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

[Rick Perley]

     Dead as doornails.  But I'll do a closer check.

     For Ken's question:  I'll check (I'm only reducing single SPWs).  
If memory serves, all SPWs in a single IF go down together.



On 08/31/2015 08:50 AM, Barry Clark wrote:
> Rick, are they dead, or merely a factor of 100 too weak?  If the
> latter, could be a sideband flipper setting error, or a LO frequency
> setting error.
>
> On 08/31/2015 08:41 AM, 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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