[evlatests] Referenced Pointing Tests

[Claire Chandler]

The trouble is that telcal might be able to get a solution but it might be 
rubbish.  I was thinking we should perhaps use the median of all subbands, 
but there's clearly some work to be done to establish what algorithm is 
best.

Claire

On Thu, 18 Nov 2010, Barry Clark wrote:

> How about letting telcal try another subband if it can't get a solution
> on its first choice?
>
> Bryan Butler wrote:
>> yes, all the solutions are written into the pointing file.  i don't know
>> that we will ever have a truly robust way of avoiding RFI, other than
>> trying to avoid where we know it exists.  we had been thinking at one
>> point of at least allowing the user to specify which subband was used -
>> if we do that is it enough?  maybe.  certainly somebody should look into
>> whether trying to take the results from all the subbands is better than
>> one, but maybe we should just go ahead now and change the recommendation
>> for RSRO/ECSO observers so that they can use the same setup for
>> reference pointing as for observing.  i suspect that the problems
>> encountered from that will be less than the problems that arise from
>> changing configurations, but maybe i'm missing something.
>>
>> 	-bryan
>>
>>
>> Claire Chandler wrote, On 11/18/10 12:18 PM:
>>> 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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