Posted by Rich on July 03, 2001 at 21:59:02:
In Reply to: Re: good VHF/UHF ducting reported for thurs 12:00 GMT posted by Nukeboy1977 on July 03, 2001 at 21:28:02:
: OK my question is. What is ducting? And what do you listen to/for? Thank you.
: Nukeboy1977
I'm certainly no expert but heres what I know.
It kinda works like this, normally VHF/UHF goes line-of-sight to the horizon and then the signal flies off into outer space. VHF actually bends some and goes a little past the visible horizon. Either way thats about as far as it normally goes.
Ducting is when theres a space between two layers of moist air (like a warm layer and a cooler layer) so the signal bounces between the two layers, think of it like a long heating duct or a hollow tube. Depending on the length of the duct the signal can go hundreds of miles well past the horizon.
This happens in the lower part of the atmosphere (the troposphere). As I understand it, the higher layers of the atmosphere doesn't have enough moisture density to make frequencies at the high end of VHF + UHF reflect and skip like the lower frequencies do.