This page only partly written.
Ducting occurs when radio signals are confined by refraction below a temperature inversion layer, or between two such layers. This can result in greatly reduced attenuation, with propagation sometimes possible at good strength over several thousand kilometres. The path between Hawaii and the west coast of the USA is one famous example of such ducting. Within southern Australia the water paths across the Great Australian Bight and from VK2 (and sometimes VK3) to New Zealand are well known, especially during summer months, but ducting can occur over land paths as well and at any time of year.
Radio amateurs who attended the Gippstech conferences in 2003 and 2004 will especially remember the presentations on ducting by Andrew Martin VK3KAQ. Andrew has revised this material into a single paper on Ducting, and this paper is available by clicking on the link below. We are grateful to Andrew for making the results of his research widely available, and also to the organizers of Gippstech for permission for us to present the work here:
"VHF and Microwave Propagation - Characteristics of Ducts" by Andrew Martin VK3KAQ