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

[Vivek Dhawan]

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?

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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