What is necessary to transmit radio waves?

To transmit radio waves, a carrier wave is essential. The carrier wave acts as the main signal that carries the information, allowing it to be transmitted over distances. When something like voice or data is sent over a radio frequency, it modulates this carrier wave, which results in the desired information being impressed upon it for broadcasting.

The carrier wave's frequency determines the characteristics of the transmitted signal and allows for effective communication over various ranges. For instance, radio stations use specific carrier frequencies to ensure that their signals do not interfere with one another, enabling clear and distinct reception of multiple broadcasts.

In contrast, the other options listed do not fulfill this role. A signal wave isn’t a standard term in the context of radio transmission; it refers instead to various types of signals that could be carried by a carrier wave. Reflective waves involve the bouncing back of waves off surfaces, which is not a necessary component of transmitting radio waves but rather a characteristic of how waves interact in their environment. Infrared waves are a different spectrum of electromagnetic waves and are not used in standard radio wave transmission, as they operate at higher frequencies and are typically utilized for different forms of communication or sensing.