Doppler effect - when an observer moves toward a stationary source https://www.youtube.com/watch?v=bg7O4rtlwEE

"Now let's see what this does to the frequency of the light. We know that even without special relativity, observers moving at different velocities measure different frequencies. (This is the reason the pitch of an ambulance changes as it passes you it doesn't change if you're on the ambulance). This is called the Doppler shift, and for small relative velocity v it is easy to show that the frequency shifts from f to f(1+v/c)... There are relativistic corrections, but these are negligible here." http://galileo.phys.virginia.edu/~pf7a/modd35.pdf

The frequency shifts from f to f' = f(1+v/c) = (c+v)/d, where d is the distance between the pulses and f is the frequency measured by the stationary observer. Accordingly, the speed of the pulses as measured by the moving observer is

c'= df' = c + v

in violation of Einstein's relativity.

The conclusion remains essentially the same even if the relative velocity v is great and the relativistic corrections are not negligible.

Pentcho Valev