Topband: Propagation Between MN and Germany

[Ford Peterson]

Thomas-KN4LF wrote:

...SNIP...

>    Another possibility is that your low angle transmitted 160 signal
passed
> underneath the Aurora oval or traversed
> in an E Valley duct.
>
> 73,
> Thomas F. Giella, KN4LF

This is very interesting to me.  "Passing underneath the Aurora Oval...."

There have been a number of circumstances, generally noticed during
contests, when the southern edge of the 'red' portion of the oval is at my
latitude, topband is almost dead.  When the 'red' portion of the oval is
well to my south, stations outside the 'iron curtain' (as the locals call
it) are very faint whispers.  Whereas stations in Canada are readily heard
and worked.  When the 'red' portion is well to my north, propagation with
both coasts is readily available--even at reduced power levels--and lower
latitude Canadians are easily worked.

I have been led to believe that the D-layer is the culprit.  "D-layer
attenuation."  This does not square with my personal experience described
above.

I have speculated that the transition point from oval to non-oval is
critical--experiencing substantial attenuation.  Perhaps it is an acute
refraction as the signal passes from one media to another, rather than
"attenuation."  Signals passing 'under the umbrella' experience a different
mode of propagation.  What is this "mode?"  What is the physical mechanism?

BTW.  After thousands of topband Qs during many contests over the recent
years, I have yet to work Alaska and only one JA.  Why doesn't this magic
"under the oval" mode work for these areas?

Ford-N0FP
ford at cmgate.com