IEC 61300-3-43:2009(E) describes the method for measuring the mode transfer function (MTF) to be used in characterising the launch conditions for measurements of attenuation and or return loss of multimode passive components. The MTF may be measured at the operational wavelengths. This standard cancels and replaces IEC/PAS 61300-3-43, published in 2006. This first edition constitutes a technical revision.