Which of the following devices would produce an RF signal at its output?

A transmitter is the device that produces an RF (radio frequency) signal at its output, which is essential for communication purposes in radio broadcasting and other RF applications. Transmitters convert audio or data signals into RF signals that can be sent over the airwaves to receivers. This conversion is critical because RF signals can propagate over long distances, enabling wireless communication.

The other options, while important in their respective roles in audio processing and reproduction, do not generate RF signals. An audio mixer combines audio signals for processing or broadcasting but does not create RF signals itself. A microphone captures sound and converts it into an electrical signal, but this is an audio signal, not RF. Similarly, a speaker converts electrical signals back into sound waves and does not produce RF signals. Thus, the only device specifically designed to produce RF signals is the transmitter.