1911
Expedition Leader
In the general case 1911 is correct in that most VHF and above signals go through the ionosphere and dont reflect back, but there is always EME (moon bounce) were you relect a signal off the moon and work station thousands of miles away. Take a lot more than a simple mobiel radio nad antenna, but can be done. A little cheaper route is by using tropospheric ducting. Ducting is where your signals can bounce off of weather patterns(high pressure systems.) Common right before or after a summer thunderstorm. I have worked TX from Ohio before. Can work into Canada pretty regularly.
Good points all, my answer was over-simplified. I thought about mentioning bouncing signals off of satellites also.