Thanks again to the website Sardegnahertz.it, there is also a database history of tx propagation, with the maps works, in English
Great findings Silvio, thanks! Ungifted mountain arrays are nasty stuff and there is no shortage in those two sites. By the way, you can acess the North Africa and Middle East website directly here http://www.ukdx.org.uk/fm/fm_index.htm
Carlos
Thanks for the link its now barred, from their corner into a new center field, another interesting website
http://www.dxinfocentre.com/tr……o_eur.html, and below their forecast for until 10th September, its full RED on the Balearis up to purple 10 and +10 including off coast of Tunisia, funny
http://www.dxinfocentre.com/tr……o_eur.html
Tropospheric (a.k.a. “Tropo”) DX modes are defined by the mechanics behind them. A Tropo DX mode is any condition that scatters, reflects or refracts signals in the Troposphere allowing long distance reception (and hence interference) to occur in the VHF, UHF and/or microwave radio bands.
Refraction occurs when the normal Index of Refraction has been altered. Vertical boundaries between different types of airmasses usually cause this…where a temperature inversion (warm air over cooler air) exists. This causes signal enhancement. When the vertical boundary becomes especially sharp, the amount of refraction becomes so severe that signals extend a great distance as though caught in a duct…thus the reference to tropospheric ducting.
Although a temperature inversion is key, the most important influencing factor is water vapour (humidity). Thus…a warm dry airmass on top of a cooler humid airmass produces the best conditions. Dry Mexican air flowing across the Gulf of Mexico or Dry Saharan air flowing across the Meditteranean are two examples of prime tropo-producing conditions. High pressure subsidence (the sinking and drying out of air)…if it occurs over the oceans…can produce reception across several thousands of km! Hawaii to California reception…both on UHF and VHF…is not as uncommon as one might think. On the other hand…high mountains can physically block tropo DX…and deserts are generally too dry for tropo. Thus…tropo is rare in the very mountainous or dry regions of the world.
As far as classifying tropo…there is not a sharp line between enhancement and ducting. Rather than classify the type using the actual physics involved, the heights of the inversions can be used as a general rule of thumb. So typically “enhancement” is caused by inversions below 450 m (1500 ft) above ground, and “ducting” is caused by inversions above 450 m. (The layer of the troposphere below 450 m is called the “boundary layer” in meteorology).
“Tropo”
