This question makes no sense whatsoever. Are you still trying to use an Arduino and nRF24L01+ to demonstrate radio doppler shifts? You must have started at least four threads on similar questions, perhaps five. Just get it clear in your head: you have no means to measure the frequency of an RF signal using an Arduino and nRF24L01+; you are flogging as dead horse here. It's pointless to keep asking how you do it because the simple answer is that you can't.