[asac][almanews]ALMA Memo 452 is available

[Larry D'Addario]

ALMA MEMO #452

Passband Shape Deviation Limits
Larry D'Addario (NRAO)

Dated 2003/04/09
Submitted 2003/04/14

Keywords: passband calibration specifications

Abstract:
Beginning with the ideal passband, which is constant
from  Nf_s/2  to  (N+1)f_s/2  and zero elsewhere, where  N=0,1,2,...
is the Nyquist interval number for sampling rate  f_s,  we examine the
effect of deviations from that form on radio telescope performance.
The implications for both continuum and spectroscopic observations are
considered.  Among the deviations of interest are: finite band edge
slope, leading to non-zero response outside the Nyquist interval
(aliasing); gain slope across the passband; gain ripple across the
passband; and mismatch of the responses among antennas in an array.
When analog filters are involved, the variation of response with
temperature is also a consideration.  Most of this report is
applicable to radio telescopes in general, but numerical examples are
selected for relevance to the ALMA telescope and specific
recommendations for ALMA are given.

Download a PDF file of ALMA Memo #452:
http://www.tuc.nrao.edu/~ldaddari/alma/memo452.pdf


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-- 

============================================================
Larry R. D'Addario
Research Engineer
National Radio Astronomy Observatory, Tucson, Arizona, USA

949 N Cherry Ave, Campus Bldg 65           7711 E Linden St
University of Arizona                      Tucson, AZ  85715
Tucson, AZ  85721-0655
tel:  +1/520/882-8250 x123                 +1/520/885-8240
fax:  +1/520/882-7955
Email:   ldaddario at nrao.edu
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