[evlatests] crossed-hand delays

[Bill Cotton]

Ken,

   Cross hand delays are harder to measure than parallel delays. Parallel
hand delay calibration is part of the standard procedures these days
but I'm not sure cross hand calibration is.  It's not something VLA
users are used to thinking about and they could easily think parallel
hand is enough.

-Bill

"KS" == Ken Sowinski <ksowinsk at nrao.edu> writes:

KS> I made a survey of crossed hand delays today and found significant
KS> errors.  At all bands, the AC error was about 10 ns, the BD error
KS> about 20 ns.  This has been corrected.

KS> The error arises when delays are repeatedly adjusted after station
KS> board reboots and power outages without giving sufficient care to
KS> changes peculiar to the reference antenna.  Crossed-hand delays
KS> were last set around March, so this represents the accumulation of
KS> such errors over eight months.

KS> The question arises of how important it is to measure these delays
KS> and keep them small.  If routine calibration includes delay fitting,
KS> for crossed-hands as well as parallel hands, when necessary, is there
KS> a need to invent a mechanism to routinely measure and correct the
KS> crossed-hand delays?  The alternative is to measure it only rarely
KS> and make corrections when it gets "too" large.

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