[asac][almanews] ALMA Memos 441 and 423 Released; Revision of ALMA Memo 438 Released

[Stacy Oliver]

ALMA Memo #441

Enhancing the Performance of the Baseline ALMA Correlator
Ray Escoffier and John Webber (NRAO)

2002/11/11

Keywords:  correlator, digital filter

The performance of the baseline ALMA correlator in spectral resolution
can be easily and inexpensively enhanced.  The time-division
architecture of the system is completely consistent with the
requirements of a so-called digital hybrid correlator.  By replacing the
present digital filter card with one of a more complex design, the
spectral resolution performance of the system could be increased by
factors as high as 32.

View a pdf version of ALMA Memo #441.
http://www.alma.nrao.edu/memos/html-memos/alma441/memo441.pdf

Download a postscript version of ALMA Memo #441.
http://www.alma.nrao.edu/memos/html-memos/alma441/memo441.ps

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ALMA MEMO #423

The Vane Calibration System Revisited
S.Guilloteau (IRAM / ESO)

2002/05/27

I re-investigate the semi-transparent vane calibration scheme proposed for ALMA, taking into account expected saturation behavior of
the receivers. This memo improves on memo 371 by using more accurate derivations and better estimates of the receiver saturation
temperatures. It is shown that to reach a given precision in calibration, the saturation on the vane must be less than this
precision. Suitable values for the vane transparencies are given. The vane transmission can be calibrated in a few minutes (at mm
wavelengths) to 1 hour (above 275 GHz) by measurement of an astronomical source (nearby quasar). A derivation of the saturation
temperature from a measurement on the vane and on an ambient load is presented. The case of partial saturation on the vane is
explored. Using the derived saturation temperature in this case requires a more accurate measurement of the vane transmission, but
is the only way to reach the specified accuracy. Given the simplicity of the vane system (passive, slow device, in the receiver
cabin), compared with the complexity, speed and location of the dual-load system, I recommend that ALMA develops and adopts such a
scheme for the receiver calibration.

View a pdf version of ALMA Memo #423.
http://www.alma.nrao.edu/memos/html-memos/alma423/memo423.pdf

Download a postscript version of ALMA Memo #423.
http://www.alma.nrao.edu/memos/html-memos/alma423/memo423.ps

________________________________________________________________________________________________

ALMA MEMO #438

Measurements of Materials for SIS Mixer Magnetic Circuits
G. A. Ediss and K. Crady
National Radio Astronomy Observatory

Revised 2002/11/14
Original 2002/11/01

Keywords: magnetic materials, hysteresis measurements

Measurements have been made of various magnetic materials in order to improve the flux density at the SIS junction positions in the
mixer. The materials measured are Hiperco 50A, HyMu 80, Consumet iron and Magnet iron. Magnet iron is recommended for unannealed
use. Consumet is recommended for annealed use. Hiperco 50A can be used annealed if large hysteresis can be accepted. For highest
flux density for lowest drive current, annealed Consumet should be used.

ALMA Memo 438 has been revised as of November 14, 2002. The new version is numbered as ALMA Memo 438.1.

To view or downloaded the revised version ( November 14, 2002), please use the following links:

View a pdf version of ALMA Memo #438.1.
http://www.alma.nrao.edu/memos/html-memos/alma438/memo438-1.pdf

Download a postscript version of ALMA Memo #438.1.
http://www.alma.nrao.edu/memos/html-memos/alma438/memo438-1.ps

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