A light source emits a series of short 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 source starts moving with (small) speed v towards the observer - the measured frequency shifts from f=c/d to f'=(c+v)/d.

Why does the frequency shift from f=c/d to f'=(c+v)/d?

If the pulses do not bunch up in front of the moving source, Einstein's relativity immediately collapses - the Doppler frequency shift can only be caused by the increase in the speed of the pulses relative to the observer (this speed shifts from c to c'=c+v). So Einsteinians are forced to teach that the pulses do bunch up:

http://www.einstein-online.info/spotlights/doppler
Albert Einstein Institute: "Next, let us look at a slightly different situation, where the source is moving towards the detector.

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

We assume that the motion of the sender does not influence the speed at which the pulses travel, and that the pulses are sent with the same frequency as before. Still, as we can see in the following animation, the motion influences the pulse pattern: The distance between successive pulses is now smaller than when both sender and receiver were at rest. Consequently, the pulses arrive at the receiver in quicker succession."

Einstein's relativity is saved but only temporarily. The assumption that light pulses bunch up in front of the moving source is false but still sounds reasonable, insofar as this assumption is correct when waves other than light are considered. In contrast, to assume that pulses bunch up in front of the moving observer is downright insane. Einsteinians are usually silent on this but sometimes they explicitly admit that no bunching up occurs when the observer, not the source, starts moving. As a result, Einstein's relativity immediately collapses:

http://www.einstein-online.info/spotlights/doppler
Albert Einstein Institute: "Here is an animation of the receiver moving towards the source.

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

(...) 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."

The speed of the light pulses relative to the stationary receiver (observer) is:

c = d/t

where t is the time until pulse and (stationary) receiver meet up. For the moving receiver, "the time until pulse and receiver meet up is shortened". This means that the speed of the pulses relative to the moving receiver is:

c' = d/t' = c + v

where t' is the time until pulse and moving receiver meet up (tt') and v is the speed of the receiver relative to the source.

The speed of the light pulses (relative to the receiver) does vary with the speed of the receiver, in violation of Einstein's relativity:

http://www.youtube.com/watch?v=bg7O4rtlwEE
"Doppler effect - when an observer moves towards a stationary source. ...the velocity of the wave relative to the observer is faster than that when it is still."

http://www.youtube.com/watch?v=SC0Q6-xt-Xs
"Doppler effect - when an observer moves away from a stationary source. ....the velocity of the wave relative to the observer is slower than that when it is still."

Pentcho Valev