[evlatests] crossed-hand delays

[Bryan Butler]

the noise sources are different for each polarization.

	-bryan


Bob Sault wrote, On 11/18/10 13:34 PM:
> 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)?
>
> --
> ----------------------------------------------------------------------
> Phone:    +61-2-98721028
> Email:    rsault at nrao.edu
> Web:      http://www.ph.unimelb.edu.au/~rsault
>
> -----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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