The Doppler effect unequivocally shows that the speed of light is not constant:

http://www.einstein-online.info/spotlights/doppler
Albert Einstein Institute: "The frequency of a wave-like signal - such as sound or light - depends on the movement of the sender and of the receiver. This is known as the Doppler effect. (...) Here is an animation of the receiver moving towards the source:

http://www.einstein-online.info/imag...ler_static.gif (stationary receiver)

http://www.einstein-online.info/imag...ector_blue.gif (moving receiver)

By observing the two indicator lights, you can see for yourself that, once more, there is a blue-shift - the pulse frequency measured at the receiver is somewhat higher than the frequency with which the pulses are sent out. This time, the distances between subsequent pulses are not affected, but still there is a frequency shift: As the receiver moves towards each pulse, the time until pulse and receiver meet up is shortened. In this particular animation, which has the receiver moving towards the source at one third the speed of the pulses themselves, four pulses are received in the time it takes the source to emit three pulses."

Since "four pulses are received in the time it takes the source to emit three pulses", the speed of the pulses relative to the receiver is greater than their speed relative to the source, in violation of Einstein's relativity..

Pentcho Valev