[evlatests] Referenced Pointing Tests

Claire Chandler cchandle at nrao.edu
Thu Nov 18 15:50:06 EST 2010 

Not yet, I think we have some tests to do first: take some data in 
extended OSRO mode and compare the median and range with what subband 2 
gives, for different frequency bands.  C-band would be the most extreme 
(with a few subbands affected by RFI).  It's not clear that X-band is a 
good test at the moment with so many of the antennas still with VLA 
receivers.

Claire

On Thu, 18 Nov 2010, 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'.
>> > > > > 
>> > > > > 
>> > > > > 
>> > > > >  _______________________________________________
>> > > > >  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
>> >
>>  _______________________________________________
>>  evlatests mailing list
>>  evlatests at listmgr.cv.nrao.edu
>>  http://listmgr.cv.nrao.edu/mailman/listinfo/evlatests
>
>

More information about the evlatests mailing list