[evlatests] crossed-hand delays

[Bob Sault]

With the switched noise source measurements, presumably the source
couples into both polarizations equally, and so cross-delays and
RL phase could be measured using this mechanism (ie correlating the
R and L of the noise source on one antenna)?

--
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Phone:    +61-2-98721028
Email:    rsault at nrao.edu
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-----Original Message-----
From: evlatests-bounces at nrao.edu [mailto:evlatests-bounces at nrao.edu] On
Behalf Of Frazer Owen
Sent: Friday, 19 November 2010 7:18 AM
To: Ken Sowinski
Cc: evlatests at aoc.nrao.edu
Subject: Re: [evlatests] crossed-hand delays


    It would certainly be best if the crosshand delays were to be small 
when the user gets the data. We can live with the current situation 
during the early days of commissioning but it seems appropriate to have 
a standard procedure which can keep the all the delays small. Maybe we 
should be getting beyond the "early days".

---Frazer

Ken Sowinski wrote:
> I made a survey of crossed hand delays today and found significant
> errors.  At all bands, the AC error was about 10 ns, the BD error
> about 20 ns.  This has been corrected.
>
> The error arises when delays are repeatedly adjusted after station
> board reboots and power outages without giving sufficient care to
> changes peculiar to the reference antenna.  Crossed-hand delays
> were last set around March, so this represents the accumulation of
> such errors over eight months.
>
> The question arises of how important it is to measure these delays
> and keep them small.  If routine calibration includes delay fitting,
> for crossed-hands as well as parallel hands, when necessary, is there
> a need to invent a mechanism to routinely measure and correct the
> crossed-hand delays?  The alternative is to measure it only rarely
> and make corrections when it gets "too" large.
>
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