Sources in EMI Analyst have different meaning, depending on the application.

For CE Analyst and RE Analyst, Sources are the current and voltage waveforms that are responsible for conducted emissions and radiated emissions. 

For CS Analyst, the Source defines the current or voltage level injected on the conductors during conducted susceptibility analyses.

For RS Analyst, the Source defines the direction, orientation, and polarization of the electromagnetic field that is impinging on the conductors during radiated susceptibility analyses.

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shield transfer impedance