We actually do specify VSWR on all of our recommended, modern mixer families (ML1, MM1, and T3). The concept of VSWR is somewhat meaningless for mixers. A mixer is by definition a dynamic impedence and is not be sufficiently described through VSWR measurements—especially since VSWR varies depending on applied signal levels. One of the most common complaints occurs when a mixer is reactively terminated at one or more of its ports with a reflective filter and poor mixer “VSWR” is blamed for the observed amplitude fluctuations. In truth, the problem has nothing to do with mixer VSWR but instead that the mixer has not been terminated with a wideband 50W load. In this circumstance, the amplitude fluctuations are actually being caused by unwanted intermodulation products lying in the stopband of the filter which have been allowed to back-reflect back into mixer. The re-mixing of this back-reflected intermodulation product leads to some very unpredictable mixer behavior and ultimately to amplitude ripple in the conversion loss. It should always be remembered that the performance of all Marki Microwave mixers are specified for wideband 50 W systems. We always recommend that a mixer be properly terminated with appropriate wideband 50 W attentuators so as to avoid problems arising from reactively terminated mixer ports.
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