When a shaker (or exciter) connects to a structure under test (SUT), the dynamic characteristics of the excitation system (shaker, stinger, and transducers) becomes coupled with those of the SUT. These couplings contaminate recorded measurements, especially while exciting light/flexible SUTs. The aim of this work is to consider interactions between excitation system and the SUT and introduce a new analytical model for prediction and hence reducing this systematic error. With the aid of this model, changes in dynamic stiffness of the SUT are estimated based on stiffness of the excitation system. The effects of excitation system location and stiffness are shown in modal testing on a free–free beam. Furthermore, influence of force transducer location is studied in the excitation system setup. The proposed method is successfully used for identification and prediction of excitation system effects on dynamic characteristics of the beam.