[mmaimcal]Re: Revised Compact Array design

[Al Wootten]

Hi John

Thanks for the new list of pad positions, which scale pads 1 to 74
radially be a factor of 1.006 to meet a new pad specification of 
15.15m--the new centers provide a minimum distance of 15.1575m--and
also alter the positions of pads 31 and 19 by 4cm E and 1 cm W
respectively.

You wrote:
   "If we wanted to be extra conservative and establish 
   a minimum of 15.20cm between pads, I would have to scale 
   radii by 1.010. Effects on beams/uv coverage are neglible.
   Again I think the losses in brightness sensitivity (2%) 
   would be OK but I would like the Science IPT leaders to sign off on 
   this. "

I think that perhaps the project will learn something about how to write
specifications from this exercise.  Specifications should be developed in
consultation with affected IPTs and should mean what they say.  Making
sure that happens is the challenge of a very distributed project such as
ALMA.

We discussed this in the NA Science IPT staff meeting yesterday and we 
believe that at this level the losses in brightness sensitivity are 
quite acceptable.

We also discussed the larger configuration (Y+); Mark and you are making
good headway in improving sidelobe levels for that.  We considered exploring
the Y+ configuration at the site in about two months.  Mark thought that
achievable; I think we should plan on an iteration mating that configuration
to the site within that timescale.

Clear skies,
Al
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| Alwyn  Wootten   (http://www.cv.nrao.edu/~awootten/)	 |
| Project Scientist, Atacama Large Millimeter Array/US   |
| Astronomer, National Radio Astronomy Observatory       |        
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