[asac] [almanews] ALMA Memos 354, 355, and 356 Released

[Carolyn White]

ALMA Memo 356

Reliability of Nanonics Dualobe Connectors

J.E. Effland (NRAO)


03/22/01

Miniature connectors manufactured by Nanonics Corporation
(http://www.nanonics.com/dualobe.html) are being used on ALMA mixers in
development at NRAO’s Central Development Lab.  These “Dualobe”
connectors have been selected for a number of spacecraft programs, which
affirms their reliability.  Connector pin damage from misalignment during
connection, which occurred on previous NRAO mixer bias connectors, is
minimized because the plastic insulator must be engaged before the pins
contact their receptacles

This report provides reliability information obtained from Nanonics for
their Dualobe connectors.  A section summarizing a visit to Ball
Aerospace, who is using hundreds of these Nanonics connectors, is also
included.

View a PDF version of ALMA Memo #356.
     http://www.alma.nrao.edu/memos/html-memos/alma356/memo356.pdf

View a html version of ALMA Memo #356
     http://www.alma.nrao.edu/memos/html-memos/alma356/memo356.html

Download a postscript version of ALMA Memo #356.
     http://www.alma.nrao.edu/memos/html-memos/alma356/memo356.ps

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ALMA Memo 355

Design of the ALMA's Compact Configuration with the Road Design First

L. Kogan 

At the recent PDR of the ALMA configurations (Grenoble, February 26-27,
2001) the committee selected the best brightness sensitivity as a main
criterion of the compact configuration design. The best brightness
sensitivity is equivalent to the most wide synthesized beam or the
smallest size of the array configuration.  The self shadowing of antennas
requires some minimum spacing between antennas. During reconfiguration
each antenna has to be accessible by the transporter. And this make even
more requirement to the spacing between antennas. So it looks like that
the problem of achievement of the best brightness sensitivity is
equivalent to the problem of minimizing area of the road inside of the
array. The previous designs of the compact configuration were leaving the
road problem to the end. At the same time the road requirement can destroy
the original good configuration. That is why I suggest to design the road
with minimum area at the beginning and then design the configuration
itself considering the roads as a topography constrain. Such an approach
can be considered as a complete design because the road area is minimized
since the beginning and therefore the brightness sensitivity is
maximized. Optimization of the side lobes can be carried out by the
standard procedure at AIPS (task CONFI) using the road constrain as a
topography constrain. The road file has to be created at the standard
Butler's format used for the site topography.

At this memo I give several examples of the roads and relevant
configurations.  The synthesized beam widths are compared with ideal
hexagon configuration beam.

One of the configurations has the beam width very close to the ideal
hexagon configuration of the given spacing.

View a PDF version of ALMA Memo #355.
     http://www.alma.nrao.edu/memos/html-memos/alma355/memo355.pdf

Download a postscript version of ALMA Memo #355.
     http://www.alma.nrao.edu/memos/html-memos/alma355/memo355.ps

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ALMA Memo #354

Choices of Antenna Size and Number for the Atacama Compact Array

Wm. J. Welch

The lack of large scale structure in array maps is the result of the
hole in the center of the visibility plane that arises because the
smallest spacing between antennas is limited to one antenna diameter.
Visibility data may be extracted for a region in the center of the hole
from a single antenna map made with one array antennas.  This can be
accomplished by Fourier transforming the map and dividing out the
transform of the gain function to produce the visibility. If a mosaic of
pointings is obtained with the array in its interferometric mode, this
data set allows extrapolation of the visibilities inward from the edge of
the hole.  This can be done by a similar procedure in which the same gain
function is divided from the observed visibilities to obtain visibilities
within the edge of the hole.  From the overlap, a complete map may be
constructed.  Pointing errors spoil this procedure.  The effect of the
pointing errors is to produce phase and amplitude errors in the
visibilities that increase toward the overlap region from both the origin
and the edge of the hole.  This is doubly bad, because the transforms of
the gain functions also tend toward zero in the overlap region and the
data errors are amplified there.  For the homogeneous array, the effects
of even small errors in pointing are severe.  The use of an array of
smaller antennas provides a better overlap in the central hole, and
reduces the effects of pointing errors.  The smaller the compact array
antennas, the better is the overlap, but more antennas are required and
calibration becomes more difficult. A reasonable compromise would be 6m,
half the 12m diameter diameter and a traditional choice.  For the compact
array to contribute a point source sensitivity that matches that of the
more closely spaced 12m antennas, the necessary number of small antennas
is approximately $(12/D_c)\times$6, where $D_c$ is the diameter of the
compact array antenna.  As an example, the compact D array of the 10 BIMA
antennas shows reasonably good overlap with Kogan's (1998) 12m D array.

View a PDF version of ALMA Memo #354.
     http://www.alma.nrao.edu/memos/html-memos/alma354/memo354.pdf

Download a postscript version of ALMA Memo #354.
     http://www.alma.nrao.edu/memos/html-memos/alma354/memo354.ps

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