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

[Walter Brisken]

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.
>> | 
>> | 
>> |  _______________________________________________
>> |  evlatests mailing list
>> |  evlatests at listmgr.nrao.edu
>> |  https://listmgr.nrao.edu/mailman/listinfo/evlatests
>> | 
>> 
>>
>>  _______________________________________________
>>  evlatests mailing list
>>  evlatests at listmgr.nrao.edu
>>  https://listmgr.nrao.edu/mailman/listinfo/evlatests
>> 
> _______________________________________________
> evlatests mailing list
> evlatests at listmgr.nrao.edu
> https://listmgr.nrao.edu/mailman/listinfo/evlatests
>