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In order to meet its cutting-edge scientific objectives, the Square KilometreArray (SKA) telescope requires high-precision frequency references to bedistributed to each of its antennas. The frequency references are distributedvia fiber-optic links and must be actively stabilized to compensate forphase-noise imposed on the signals by environmental perturbations on the links.SKA engineering requirements demand that any proposed frequency referencedistribution system be proved in "astronomical verification" tests. We presentresults of the astronomical verification of a stabilized frequency referencetransfer system proposed for SKA-mid. The dual-receiver architecture of theAustralia Telescope Compact Array was exploited to subtract the phase-noise ofthe sky signal from the data, allowing the phase-noise of observationsperformed using a standard frequency reference, as well as the stabilizedfrequency reference transfer system transmitting over 77 km of fiber-opticcable, to be directly compared. Results are presented for the fractionalfrequency stability and phase-drift of the stabilized frequency referencetransfer system for celestial calibrator observations at 5 GHz and 25 GHz.These observations plus additional laboratory results for the transferredsignal stability over a 166 km metropolitan fiber-optic link are used to showthat the stabilized transfer system under test exceeds all SKA phase-stabilityrequirements under a broad range of observing conditions. Furthermore, we haveshown that alternative reference dissemination systems that use multiplesynthesizers to supply reference signals to sub-sections of an array may limitthe imaging capability of the telescope.

Astronomical verification of a stabilized frequency reference transfer system for the Square Kilometre Array