The frequency of a photon is determined by the energy emitted by an electron when falling from one shell to a lower one divided by Planck's constant.
First, how does a single fall of one electron cause a frequency? I would think the electron would have to jiggle up and down to bring about a frequency.
Next, what is the difference between a photon's frequency and the frequency of the electromagnetic radiation itself? Are they one in the same? It appears that the photon has an internal frequency of its one, while there is a second frequency that would be how often the photons are created by the falling electrons.