I am a beginner to Experimental Modal Analysis and I have a scaled miniature frame and my objective is to conduct modal identification under the structure's operating condition using Frequency Domain Decomposition (FDD). However, after I expose the structure and take the reading, the results almost have no information about modal parameters. Questions: 1. In case 1, there is only one peak in the response, whereas the system is a 2DOF system. What could be the reason? 2. In case 2, I could not see any peaks in the 1st singular values of the matrix, where am I going wrong? 3. What is the sensitivity of the acceleration transducers required for scaled experiments? Are the sensors, sensitive enough? 4. Is the frequency response just due to the intrinsic noise of the accelerometer? 5. Also, why is there a peak in the PSD at close to 0hz? 6. Can I use FDD for laboratory based experimental modal analysis without any external random excitation? 7. Should I excite the scaled model with random input force and then do output only modal analysis? I have attached my setup, results and questions. https://drive.google.com/file/d/0B-25vDIilD9FM1NuXzNwX2dEY00/view?usp=sharing [Broken] Thank you, Chaitanya How can I do modal identification of a scaled miniature steel frames using FDD technique under ambient vibration? - ResearchGate. Available from: https://www.researchgate.net/post/How_can_I_do_modal_identification_of_a_scaled_miniature_steel_frames_using_FDD_technique_under_ambient_vibration [Broken] [accessed Jul 6, 2015].