Fluctuations of water vapour content in the troposphere are one of the worst enemies of millimeter/submillimeter aperture synthesis observations, being responsible of loss of coherence in the radio signal and limiting the spatial resolution. The use of the fast switching technique tries to minimize this effect through fast and succesive cycles between calibrator and source. Here we present fast-switching tests in millimeter/submillimeter wavelengths carried out at the Submillimeter Array (SMA)

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... n top of Mauna Kea, in order to shed light into the optimization of calibration cycle as a function of different atmospherical conditions. We have found that fast switching with calibration cycles of a few minutes slightly improve (∼ 15%) the signal-to-noise ratio in the image plane with respect to the standard calibration time of 20-30 min, under relatively good weather conditions. For worse weather conditions, the fast switching technique does not have any relevant effect. This confirms previous findings that most of the fluctuations must be shorter than 2 minutes under normal conditions in the Mauna Kea site and baseline range from ∼ 20 -200 m.