with FM the frequency is compressed by the movement of the aircraft due to doppler shift.#
with all due respect this is total rubbish- given that radio waves travel at the speed of light (300,000,000 meter per sec 186000mps), the effect of an aircraft travelling at 500 knots would not have any noticable impact.
Bren - we proved it on a few occasions when operating special prefix stations on 7Mhz /3.5 Mhz SSB - our young lady consistently would get far more responses to a CQ in really poor condx than the rest of us would .... got better reports and seldom got asked for repeats....
......or maybe it was just that she had a real sexy voice!
73 G4OTU