ALMA Memo #304

Relative Sensitivity of Double- and Single-Sideband Systems for both Total Power and Interferometry

Comparison of double-sideband and single-sideband receiving systems shows that the ratio of sensitivities is proportional to the inverse ratio of the system temperatures. In the case of interferometers, where the complex cross correlation is measured, there is an additional factor of the square root of two by which the sensitivity of double- sideband systems is reduced. This factor, which is not always taken into account, does not apply to total power systems. The relative sensitivity of double- and single-sideband systems is discussed for observations of both continuum and spectral line radiation. The results are then generalized to the intermediate case of unequal sideband gain. Finally, numerical results for ALMA from earlier memos are reviewed and extended.

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Last modified: April 25, 2000