On 6m it is amazing how much Doppler there is on longer distance GDX stations. The screenshot shows just how much Doppler there is on G4BRK's signal today. There were something like 6 aircraft involved at times with WSPR managing to decode when the Doppler is low. On more local signals (e.g. G4FGJ) there is much less (or nil) Doppler. Clearly aircraft reflection plays an important part in long GDX paths. I have no idea where these planes are located.