The E5072A option 008 enables to set the receiver frequencies independently from where the source frequency is tuned. This ability is important for harmonic distortion measurements and for measuring frequency converting devices such as mixers and converters. Advanced calibration techniques for the E5072A, such as scalar mixer calibration (SMC) or vector mixer calibration (VMC), require this option. You can upgrade the option by ordering E5072AU-008 for your E5072A.