Guy Atkins wrote:

This is excellent reading; thanks for pointing out the link.

I do have "issues" with the second illustration, though. 14 longpath F1/F2
layer hops to get from transmitter to receiver is not a proven fact. The
author's modelling program is necessarily based on classic propagation
theory, but doesn't address the possibility of signal "ducting" between the
layers.

If so many multiple hops are required, why don't we hear echoing and
experience severe signal fading on HF on a regular basis? The multiple
arrival angles of the signal at the receiver would strongly suggest this.
However, experience shows that longpath reception is no more prone to fading
& echoes than a path of one or two hops. In fact, almost all longpath
signals I've encountered have a smooth, and often rapid (10-20 minutes) rise
in signal strength, and then a gradual decline, without major fading or
fluctuations as you would expect in the classical model.

I'm inclined to believe that ionospheric ducting is more the norm than the
exception, as theorized by Yuri Blanarovich a few decades ago.

Much more on this subject can be read in two excellent, detailed (& lengthy)
articles on tropical bands propagation, written by John Bryant and David
Clark for Fine Tuning's "Proceedings" in the early 1990s. I was on the
editorial staff through those years and was fortunate to be have access to a
lot of the background information Bryant and Clark used in their articles.

I'm more of a believer in ducting myself, rather than hops.

dxAce
Michigan
USA