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

[Barry Clark]

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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>>
>>
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