[evlatests] Referenced Pointing Tests

[Bryan Butler]

not much data to be mined, but it would be interesting.

	-bryan


Barry Clark wrote, On 11/18/10 13:47 PM:
> OK, somebody could mine the data, and see if median is detectably
> different from first good.
>
> Bryan Butler wrote:
>>
>> i've always thought the median is the simplest good filter - i suspect
>> we'll find no better.  should i ask keith to implement that for testing?
>>
>>      -bryan
>>
>>
>> Claire Chandler wrote, On 11/18/10 13:41 PM:
>>> 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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