The R&S FSUP-B60 option provides the Signal Source Analyzer R&S FSUP with two parallel receive paths. You can perform crosscorrelation between the two paths owing to the symmetrical structure, and eliminate the uncorrelated inherent noise of the two reference sources. This significantly increases sensitivity, which is no longer limited by the phase noise of the internal references. The degree of improvement depends on the number of averages and can be up to 20 dB.