Art Unwin wrote:
Interesting you
quote the electron gun. ... So where did this photon emerge from?

The electron is the gun, the photons are the bullets.
Quoting Feynman's "QED": "So now, I present to you the
three basic actions, from which all of the phenomena
of light and electrons arise.

-Action #1: A photon goes from place to place.
-Action #2: An electron goes from place to place.
-Action #3: An electron emits or absorbs a photon."

For an RF antenna radiator, the electrons go from
place to place in (on) the conductor in the form
of free electrons. The photons go from place to place
in the space surrounding the conductor. Only the
photons can move at the speed of light from the
feedpoint to the ends of a dipole. Electrons move
hardly at all.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com