[asac] comments on report

[Al Wootten]

Hi, Chris

Some comments on your comments...

"On page 8, maybe I'm just still confused about the correlators, but I have a
question. Does the reprogramming of the baseline correlator give you the same
total efficiency as the Future or Enhanced correlator, albeit with many fewer
channels and some restriction on total bandwidth? If so, it would be nice to
say so CLEARLY in our report. "

Well, there will be differences in the tenths to one per cent range between
the reprogrammed baseline correlator and the Future and Enhanced Correlators
in the higher resolution lower bandwidth modes which depend upon the details
of the sampling, FIR filtering, etc.  but yes the number of channels and
bandwidth gets halved more or less (details depend on things such as the
number of wires, etc), as calculated by Ray for the table I presented.  This
will be presented as a memo soon.  I've contributed to the confusion, I'm
afraid, by dribbling this information out before the memo was written.
Additionally, of course, the ability to record data at a maximum rate of
something like 60 MB/s will limit the ability to make full use of many
additional channels.  This limit should be relaxed as Moore's law enables us
to record more and more data in the future.  I see I left this in my
outbox too long and Hasegawa has already commented on it!

"Still on page 8, if we expect the correlator plans and costs by only 
September 2002, then we ought to specify frequent reports as to their 
progress. I see this situation as rather like the configuration issue; we 
start off with two competing designs and, if we're lucky, they will 
converge to something better than either initial design."

And the ASAC should examine the 'big picture' of data recording, archiving
and reduction procedures in parallel with consideration of the higher
data rates from baseline/future/enhanced correlator designs.  Some of
this should begin with next month's discussion.

"In the polarization section on page 12, I think it's important to explore 
the issue of rotating some receivers by 45 degrees a little bit more. In 
particular, the Receiver group could be asked to see whether band 7 could 
be rotated without impacting the optics etc. Someone else could look into 
whether the 45 degree phase rotator would in fact be inexpensive and 
low-noise. Perhaps this is something for the polarimetry group (when it 
is set up) to focus on."

The receivers and optics are a package and no mechanical rotation whatsoever is
possible.  Some receivers may be installed at a 45 degree angle; this
is the only option.  The ASAC could charge the JRDG to consider the issue
of the phase rotator in collaboration with the polarimetry group.

Clear skies,
Al