[asac][almanews] ALMA Memo 416 Released

[Stacy Oliver]

ALMA Memo #416

The Relative Sensitivity of Full-Wave and Half-Wave Detectors in Radio
Astronomy

A. R. Thompson (NRAO) and D. T. Emerson (NRAO)

02/04/03

Keywords: sensitivity, linear detectors, square-law detectors,
half-wave, full-wave

The sensitivity in the measurement of Guassian noise power using a
half-wave detector can suffer degradation relative to that of a
full-wave detector, in cases where the bandwidth if the input waveform
is not small compared to the center frequency.  There are two physical
mechanisms that suggest a basis for this effect.  The half-wave detector
responds to only half of the input waveform, resulting in possible loss
of information.  Also, in the half-wave detector a component of the
input spectrum feeds through the diode and adds to the noise that is
subsequenctly filtered by averaging at the detector output.  This
feedthrough component does not occur in full-wave detectors.  The
phenomena are examined using an analytic method developed by Nuttall
(1986), and also by numerical simulation.  The results for both linear
and square-law characteristics are considered, and formulas and graphs
for estimating the magnitude of the effects are given.

View a pdf version of ALMA Memo 416.
http://www.alma.nrao.edu/memos/html-memos/alma416/memo416.pdf

Download a postscript version of ALMA Memo 416.
http://www.alma.nrao.edu/memos/html-memos/alma416/memo416.ps


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