Tropospheric ducting is when a radio signal gets bent in the atmosphere instead of going in a straight line like it usually does. Normally VHF and UHF signals only go in a straight line out to the horizon, so if you're behind the horizon (or a mountain or a lot of tall hills or whatever) you don't see the signal. A duct is created by disturbed weather which bend the signal that's going up into the atmosphere and bounces it back to earth further away from where it would normally be able to go. Think about what would happen if you were shining a flashlight up into the air. Nobody on the ground could see it. But, if there was someone with a giant mirror up there somewhere, they could bounce it back down to someone a long way away. That's oversimplified, but that's the general idea.
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Date: 2008-04-29 09:52 am (UTC)