The state-of-the-art OMA algorithms have been used to identify the dynamic parameters from output-only vibration data acquired in a testing campaign carried out on a remarkable 368 m high steel structure, namely, the Riga Television and Radio transmission tower. The structure is unique both in terms of the structural system and of societal relevance since it is a historical monument and a landmark for Riga, one of the capitals of the Baltic States. Two independent acquisition systems were used to measure the vibration responses of the tower at a total of 48 DOFs along its height. Each acquisition system is constituted of two 3D vibration sensors. One of the acquisition systems is used as a reference, and the other one is a moving system. The latter was relocated to different stories and antenna, and the former remained at the same (reference) storey throughout the test. Because the two different systems were not synchronized, advanced post-processing techniques were employed to synchronize the different datasets and subsequently identify the global modal properties of the tower