What component of a TACAN system converts data into serial data?

The data output circuit is integral to a TACAN (Tactical Air Navigation) system as it enables the conversion of data into serial data format. This is essential for effective communication and transmission of navigational information. By converting the received data into a serial format, the system allows for clearer and more efficient handling of the information, which can then be processed by various equipment and devices used for navigation.

In the context of TACAN systems, the data output circuit ensures that the transmitted navigation signals can be understood and utilized by aircraft and ground stations. Serial data transmission is preferred in many systems because it simplifies the design and reduces potential errors in data transfer.

The other components listed, such as frequency modulation circuits, signal amplifiers, and tuning control circuits, serve different specific roles within the TACAN system, but they do not perform the function of converting data into serial format. Therefore, the data output circuit is identified as the correct answer to this question.