[evlatests] Referenced Pointing Tests

[Barry Clark]

Are rubbish solutions a problem?  How often do they occur?  Does anybody
have any data?

Claire Chandler wrote:
> 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'.
>>>>>
>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> evlatests mailing list
>>>>> evlatests at listmgr.cv.nrao.edu
>>>>> http://listmgr.cv.nrao.edu/mailman/listinfo/evlatests
>>>>>
>>>> _______________________________________________
>>>> evlatests mailing list
>>>> evlatests at listmgr.cv.nrao.edu
>>>> http://listmgr.cv.nrao.edu/mailman/listinfo/evlatests
>>> _______________________________________________
>>> evlatests mailing list
>>> evlatests at listmgr.cv.nrao.edu
>>> http://listmgr.cv.nrao.edu/mailman/listinfo/evlatests
>> _______________________________________________
>> evlatests mailing list
>> evlatests at listmgr.cv.nrao.edu
>> http://listmgr.cv.nrao.edu/mailman/listinfo/evlatests
>>