delighted to answer
Hi Intoelectrics the speed of light is a constant (not a maximum) this information comes from various researchers working in different fields of radio/wireless . (which I did myself at one point.) The radio system we use in this day and age is according to my understanding essentially that developed by Marconi in an effort to circumnavigate some 17 of Nikola Tesla's wireless patents.
The present system is essentially parallel tuned into a resonant antenna , propagation is mostly via transverse wave via the ionosphere with a very small % ground wave, the assumed speed of propagation of the electromagnetic wave is the speed of light.
Tesla's wireless system however used series resonance and was tuned to a resonant ground antenna. propagation is mostly via the longitudinal wave via the ground plain. with a very small ionospheric % transfer. the speed of transmission is pi/2 x speed of light. Transmission being via the electrostatic wave
FYI here is that that transmission system described and demonstrated many years ago now by Eric Dollard although it been substantiated many times by different researchers .
faster than light
kind regards Duncan