This application note discusses how high source harmonics may interact with the out-of-band comeback characteristics of a filter under test to affect the filter transmission measurement. A low-pass filter is used to reduce the source harmonics injected into the filter to show the effect that lowering the harmonic content would have on the cutoff band measurements. The ShockLine MS4652xB VNAs now have a new High Fidelity mode that reduces source harmonics in a key frequency band to help improve filter dynamic range tests like the one described in this application note.

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