In the case of a 45 kW broadcasting antenna emitting radio waves at a frequency of 4 MHz, the quantum nature of electromagnetic radiation is generally not important in analyzing the radiation emitted from the antenna. Quantum effects typically become significant when dealing with extremely high energies or very small scales, such as those encountered in atomic and subatomic interactions.
For radio waves at frequencies in the MHz range, the quantum mechanical behavior of electromagnetic radiation, as described by photons, is typically negligible. At these frequencies, the wave nature of electromagnetic radiation is well-described by classical electrodynamics and Maxwell's equations.
Quantum effects become more significant as the frequency of the electromagnetic radiation increases, such as in the case of X-rays, gamma rays, or visible light. At those higher frequencies, the particle-like behavior of photons and quantum phenomena become important in describing interactions with matter.
However, for the relatively low frequency of 4 MHz associated with the broadcasting antenna you mentioned, classical electromagnetic theory and wave-based models are sufficient for analyzing and understanding the behavior of the radio waves emitted by the antenna. Quantum effects are not necessary to consider in this context.