Consider a light source emitting a series of pulses the distance between which is d (e.g. d=300000 km). A stationary observer (receiver) measures the frequency of the pulses to be f=c/d:

http://www.einstein-online.info/imag...ler_static.gif

The observer starts moving with speed v towards the light source - the measured frequency shifts from f=c/d to f'=(c+v)/d (Doppler effect):

http://www.einstein-online.info/imag...ector_blue.gif

The speed of the pulses relative to the observer is

c' = df' = c+v,

in violation of Einstein's relativity:

http://a-levelphysicstutor.com/wav-doppler.php
"vO is the velocity of an observer moving towards the source. [...] Hence, the velocity of waves relative to the observer is c + vO."

http://physics.bu.edu/~redner/211-sp...9_doppler.html
"Let's say you, the observer, now move toward the source with velocity vO. You encounter more waves per unit time than you did before. Relative to you, the waves travel at a higher speed: v'=v+vO."

Pentcho Valev