[evlatests] [Fwd: Failures to Tune, at Q-band]

[Rick Perley]

    Two important typos were in my earlier report.  Please delete that 
one, and use the following instead ...

-------- Original Message --------
Subject: 	[evlatests] Failures to Tune, at Q-band
Date: 	Mon, 28 Nov 2011 11:39:31 -0700
From: 	Rick Perley <rperley at nrao.edu>
To: 	evlatests at aoc.nrao.edu



    The Wednesday evening calibration test cycled through the 8 bands, 
at a rate of one per minute.  Previous tests used the cycle: 

    X -> C -> S -> Ku -> K -> Q -> Ka -> L  --> X

    and resulted in a high fraction of tuning failures at Ka band on B/D 
side only.  Note that this IF was tuned to 29.4 GHz, while the AC side 
was at 36.4 GHz.  The preceding band was Q, and the frequencies were 
47.9 and 41.9 GHz on the AC and BD IFs.

    For this new experiment (run Wednesday night), I perversely reversed 
the order of the tuning sequence, to see what this would do.  So, the 
order was now: 

    X -> L -> Ka -> Q -> K -> Ku -> S -> C -> X

    For this ordering, the failures to tune are profoundly different!  
The failures now occur at Q-band, on the B/D side only.  The frequencies 
tuned were 47.9 (AC) and 41.9 (BD), while the preceding band (Ka) used 
the same pair as listed above:   36.4 GHz (AC) and 29.4 GHz (BD).      
There were 37 separate scans, and the total number of failures was 55 -- 
a failure rate of (55/(26*37)) = 5.7%.  Far too high!  And none of these 
failures was flagged by the on-line system.  The failures are uniformly 
distributed over the antennas -- only two antennas showed no failures (1 
and 28), while one antenna had five (ea04) and two antennas had four (26 
and 22). 

    No other band showed an unusual number of tuning failures. 

    It would be good to end this problem.  And it would be useful if 
these failures could at least be detected and flagged by the on-line 
system. 
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