Cables are essential in civil engineering for constructing slender, lightweight structures with large spans. To ensure serviceability and load-bearing capacity, a monitoring of the cable forces is necessary. Conventional, static methods are not suitable for systems with highly pre-stressed cables or large cable diameters, so dynamic measurements using the cable's vibration behavior offer an alternative. This study presents laboratory test results on inverse identification of cable forces using eigenmodes and the corresponding frequencies, comparing contact and non-contact dynamic measurement methods. Two methods for determining the cable force will be investigated within this study: (1) the linear theory of vibrating strings neglects internal sag and bending stiffness, and (2) an inverse identification of the cable force for a cable tensioned on both sides, accounting for bending stiffness. Contact based measurement with accelerometers can identify many eigenmodes and frequencies unambiguously and is suitable for simple systems like single span systems. In the conducted investigations, the non-contact measurement with microwave interferometers could only identify up to 4 natural frequencies. The study also examines the influence of the free vibration length, which, in addition to the bending stiffness of the cable, the fork fitting and utilization, has a significant influence on the determined cable forces. The implications for using different fork fittings and cable cross-sections are discussed. This study offers valuable insights into the challenges and limitations of cable force identification and highlights the importance of choosing the appropriate measurement method based on the design of the cable structure.