[mmaimcal] Antenna specification question

[Al Wootten]

Hi Rob

Thanks for the comments.

In fact, we originally had no nutators on any of the MMA telescopes.
At a review in July? 1999 we were told that we needed to have nutators on all
the telescopes.  However, they are prohibitively expensive.  From our
early estimates of how much total power continuum ALMA would do we set the
spec you cited.  I think the five which ALMA is purchasing cost (total) 
~$850K or so ballpark.  Fifty more would exceed the cost of an antenna.

The four Total Power antennas are also equipped with the best receivers,
from a point of view of 1/f noise.  ALMA-JP are doing a study of how
much integration the Total Power and ACA arrays really need to do to
provide good images for different sorts of projects.

I think that in the best of all possible worlds, all antennas should meet
all specifications.  In order to deviate from this rule, there should be
a quantifiable benefit.  If we hear what that benefit might be we can
compare benefit with loss.  

Clear skies,
Al

Rob Reid writes:
 > Hi,
 > 
 > At 2:27 PM EST on November 3 Al Wootten sent:
 > > Q:  Does the ALMA production antenna have to meet all specifications
 > > when equipped with a nutator?  If not, the design of the quadripod might
 > > be optimized for performance without the nutator.
 > 
 > If the demand for total power exceeds what the ACA can provide, it would be
 > nice to be able to upgrade a few ALMA antennas with nutators.  This is
 > especially true if OTF mapping with ALMA can't be done fast/stably enough to
 > get total power, given that the two different types of ALMA antennas might
 > drive differently.  Admittedly putting nutators on some of the antennas would
 > probably add to that problem.
 > 
 > > The specifications are unclear on this, but the point of view so far is that
 > > it must meet all specifications when equipped with a nutator.
 > 
 > I'm new at digging through the ALMA specs, but according to
 > SCI-90.00.00.00-0230-00, "at least 4 antennas must be equipped with wobbling
 > subreflectors".  "at least" implies that more might be needed if 4 turns out to
 > not be enough.  If the production companies are really keen to further split
 > their designs into nutatored and nutatorless, then presumably they'd need an
 > agreement on how many nutatored antennas each company is responsible for.
 > 
 > -- 
 > Rob Reid		A NRAO NAASC ALMA PDF		@   @  @ @  @   @
 > 1-434-244-6822	       	http://www.cv.nrao.edu/~rreid/  ^   ^  ^ ^  ^   ^
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