What does the term "analog" refer to in radio communications?

In radio communications, the term "analog" refers to the variation or modulation of a signal. This means that the information is represented in a continuous signal that can take on any value within a range, as opposed to being represented in discrete steps or digital format. Analog signals change smoothly over time and can represent various types of information, such as voice, music, or other audio signals, by modulating properties like amplitude, frequency, or phase.

This characteristic of analog signals allows for a more natural representation of sound and other continuous phenomena, making it suitable for traditional radio communication methods. When an analog signal carries information, it involves variations that reflect changes in the amplitude or frequency of the wave, effectively encoding the desired information.

Other options pertain to different concepts in communication systems. For instance, binary data conversion relates to digital communication, where information is represented in discrete binary values (0s and 1s). Simplex communication refers to one-way communication, and time-division multiplexing involves sharing a communication channel among multiple signals by allocating time intervals for each signal. These concepts are not directly related to the definition of "analog" in radio communications.