[evlatests] Referenced Pointing Tests

[Claire Chandler]

Hi Rick,

You need to define what you mean by "works for wideband".  Recall that at 
present the default algorithm in TelCal is to take the second subband from 
the bottom of each baseband for the solution that is fed back to the 
online system.  Therefore it relies on that subband being RFI-free.  I 
believe that solutions are being written for all subbands for testing 
purposes at the moment, and what we really need to do is to establish how 
to combine the results from all those subbands to obtain a solution that 
is not affected by RFI, and can potentially be used to enable pointing on 
weaker sources.

Claire

On Thu, 18 Nov 2010, Rick Perley wrote:

>    I ran a test of referenced pointing this morning.    There were two
> goals:
>
>    1) Does 'wide-band' referenced pointing work as well and reliably as
> 'narrow-band'?
>
>    2) Does a 15-second cadence work as well as 20-second?
> (Explanation:  In the past, the system used 10 seconds to move from one
> position to the other, and 10 seconds to integrate.  But from holography
> we know that the move-and-settle time is less than 5 seconds, so a
> 15-second (5+10) regimen should work).
>
>    To test these, I used 3C147 (~5 Jy) to measure pointing offsets at
> X-band, with four combinations:
>
>    1) Narrow-band with 20 seconds.
>    2) Narrow-band with 15 seconds.
>    3) Wide-band with 20 seconds
>    4) Wide-band with 15 seconds.
>
>    The intention was to observe each mode sufficiently long for 3
> consecutive pointing solutions.  Due to a blunder on my part, the 'fast'
> tests were observed long enough for only 2 solutions.  But that is still
> sufficient for the following conclusions:
>
>    A) Wide-band mode works as well as narrow-band.
>
>    B) Fast mode appears to be as good as 'slow'.
>
>    There were a few failed solutions for all four trials -- the
> statistics are not good enough to claim that any one of these four is
> better or worse than the others.  Comparison of the actual solutions has
> been done for only one antenna (so far) -- there is no significant
> differences, other than an expected change in elevation offset as the
> sun rose.
>
>    By looking at the detailed log, the sequence of operations is easily
> discerned.  (Ken claims this may be unreliable, and he intends to peer
> deeper after lunch).  But, be this as it may, I deduce that the
> *absolute minimum* time needed for a single referenced pointing
> measurement is (presuming the antennas are on source) is:
>
>    124 seconds for 'slow' mode,
>    94 seconds for 'fast'.
>
>
>
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