[mmaimcal] forwarded message from Naomasa NAKAI

[Al Wootten]

Some corrections to a misunderstanding on my part, and some more information
from Nakai-san.  Al
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From: Naomasa NAKAI <nakai at msv1u.nro.nao.ac.jp>
To: awootten at NRAO.EDU
Cc: lmsa-shoi at nro.nao.ac.jp, lmsa-pro at nro.nao.ac.jp
Subject: [asac] ALG Issues
Date: Thu, 22 Jun 2000 01:09:00 +0900 (JST)



Dear Al,


(1) I read your detailed comments on 'Plan for an Enhanced ALMA' 
presented 12 June 2000 by Japanese members.  Most of them are very 
interesting for me, but I would like to comment on one thing;

  "c. Implementation
        1. Japan has proposed providing these antennas over the period
           FY2002-2008."
           
in your e-mail is not correct.  At least, on 12 June, we has not proposed
that Japan will provide the antennas of a compact array but proposed
that Japan will provide 1/3rd of the total number of the 12m + 6m/8m
antennas, i.e., 1/3rd of 85 (or 88 in your mail).  We know that the 
antennas of the baseline ALMA proposed by US and Europe is 64 and do not
include small antennas, and that a compact array is realized in the 
enhanced ALMA in which Japan participates.  However, this does not mean 
automatically that Japan will provide the compact array, we think.
It can be understand that one of Japan, US, or Europe should construct
all the small antennas, because the number of the antenns is only several
or about 10.  However there is a possibility that all (or two) of the 
three partners participate in its design and share the cost but only one
partner constructs all the antennas.  I think that which partner provides
the small antennas should be discussed in ALG or ACC and that ASAC discusses
only how important (or not important) the compact array is and its 
specification.


(2) After the teleconference on 12 June, our correlator group led by
Chikada and Okumura (not Okamura) made further study and had the following
idea to reduce the cost of proposed FX, keeping science merits.  I tranfer
their report to ASAC and please consider:

===============================

There were disscussions whether it is appropriate or not to have the
correlator capability of 128k channel/IF, considering the costs. Thus we
have started to discuss several possibilities to reduce the cost without
loosing the scientific merits. We are happy to report:

1). We are studying various possibilities to reduce the costs, and we
found a method to reduce the costs, in principle, by a factor of several,
 maintaining the total bandwidth of 16GHz and the minimum frequency
resolution of 32kHz simultaneously, i.e., without loosing the scientific
merits which we have emphasized.

2). The method is to have frequency region bunching -- either smoothing
or frequency baseline calculation -- just after the cross-correlation
multipliers to reduce the number of words of the accumulation memory
whose cost is nearly 80% of the total cost of the enhanced-ALMA FX 
correlator (i.e. the second generation correlator we proposed).  This will 
also eliminate the fear that the large amount of the frequency channels 
might increase the costs of post-detection computings and archivings.

3). We will study the above possibilities and will report the results to
the ALG meeting and others.

======================================================

All the best,

Nakai



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