Skip, Thanks for the UHF screenshots. There has to be motion or change taking place within the refractive medium to cause Doppler and it would seem this holds true for the type of atmospheric enhancement found on VHF/UHF. I can see why it's necessary to use the most robust modes if both Doppler spread and Doppler shift are present much of the time; I'm sure aircraft scatter is no help either.
Speaking of aircraft reflections; I recorded a short video of the effect today using a local 2 meter beacon as the signal source (see link below). The beacon is only 10 miles from my home and the AC Doppler can be quite strong; often competing with the S9+ signal. You can hear (and see) the two signals beat together as the AC Doppler sweeps across the spectrum. There's quite a bit of air traffic out this way so it would be easy to test how much of an effect this has on digital. I'll have to pursued a local buddy of mine to participate. Long distance VHF/UHF will have to wait until I can find a place for my Yagi's. Aircraft Doppler recording -- http://www11.zippyshare.com/v/10329668/file.html 7 Zip extraction utility -- http://downloads.sourceforge.net/sevenzip/7z465.exe Tony -K2MO
