[alma-config] CoDR agenda

[Leonia Kogan]

Min,

I think you take into account the possibility to use the pads of the
inner circle of larger configuration as pads for the outer circle of
the less configuration when you are comparing the number of pads.  As
you may remember I showed in my memo 226 that around 25% of the pads
can be shared (saved) by this way.
 
The percantage of number of shared (saved) pads can be more by fixing
more shared pads. The question is how much the array's parameters will
be agravated.

My filling is that having 64 antennas (only 36 used in my memo 226) we can save much more pads than 25%.

Leonia


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>From owner-alma-config at kochab.cv.nrao.edu Thu Mar 16 13:08 MST 2000
Date: Thu, 16 Mar 2000 13:07:23 -0700 (MST)
From: Min Yun <myun at aoc.nrao.edu>
Reply-To: Min Yun <myun at aoc.nrao.edu>
Subject: Re: [alma-config] CoDR agenda
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Cc: alma-config at zia.aoc.NRAO.EDU
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John,

You are probably on your way home by now, but I would comment
briefly on some of the points below so my counterarguments are
well known to everyone.

> 2) If the imaging simulations is a 'draw' I would argue that 
> zoom arrays are preferable to fixed arrays, first  because it
> gives the option of extra science capabilities (adjustable resolution, 
> matched uv coverage in arrays, avoidance of tapering), and  secondly it 
> requires fewer pads (and more importantly number of antenna moves to 
> cover through all  resolutions). Finally if one bulids a zoom geometry and  
> the continuous moving mode proves impractible then one can decide
> to run it as a set of 5 (or whatever number one chooses) fixed arrays. 

> 
> 3) I thought we had discussed the real estate question
> a few weeks ago. Assuming there is a limited 3km area then the largest 
> array should obviously have all the antennas on the perimeter to get max
> resolution. The conceptual spiral in my memo 283 moved gradually from a 3km 
> spiral to a 3km ring to give the last factor of 2 in resolution. As I
> note in my strawman layout memo (292) an extra 20-30 pads are probably
> needed to be placed around the perimenter of the 3km 5deg gradient 
> area to get  max resolution for this largest array. Given the shape
> of the terrain this largest array will look like some form of 
> triangle.
> 

Your argument in favor holds only under the perfect ideal case,
and the supposed advantage is not soundly based on reality in terms
of expected resolution demands, etc.  
The numbers of pads needed for the current strawperson donut design
is 192 (vs 180 in your case), so the difference is not large.  If
you need further 30 pads for the 3 km ring, then the zoom spiral
design actually requires 18 additional pads.  By the way, the 
192 pads needed for the donut configurations also include all of the
pads needed for the compact configuration as well.  Running the
zoom spiral as set arrays pays a big price in resolution (by a
factor of 2), which is a serious concern for me and others.

I would like to lay out all these (and operational) issues during
the second day so that we can truly evaluate the costs and benefits
of the two concepts.  Ultimately the imaging performance should 
determine the final choice, but other issues may become important
if the imaging performance are simply not too different.




					-- Min



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