Fe/amorphous FeCrB multilayers were studied by ferromagnetic resonance measurements as a function of the interlayer thickness. The experimental determined value of (4ΠM)eff was compared with that computed from a model corresponding to a layered structure, built up of perfectly homogeneous and strongly coupled interlayers. The agreement is satisfactory except for too thin FeCrB or very thick Fe layer thickness, a result explained by the crystalline structure of the Fe interlayers. Generally in perpendicular resonance a well defined standing spin wave spectrum is detected from which the value of Aeff was extracted. Some anomalies of the spectra are also presented.