TopBand: Mirror earth

[Dan Robbins]

Some seem to have the impression that a signal bouncing off the earth can
only do so with a tremendous loss.  According to the Radio Propagation
Handbook, this isn't so.  Remember we're talking Top Band here and with
common radiation angles, say 10 to 50 degrees.  Under those conditions a
seawater reflection has 0.1 dB or less loss.  In the absence of ionospheric
absorption, it is expected that over mostly water paths the signal levels at
amateur power levels on the low bands will exceed S9 on paths well in excess
of 10,000 miles.  The lossy parameter in this equation is not Mirror Earth.
Land reflections due impose a penalty anywhere from a couple to a few dB per
hop.  Fortunately, we live on watery planet.

If ducting were a common phenomenon, there would be no difference between
long over water and over land paths.  Yet, there is a difference; DXers
certainly know this and it has been documented.  This can only be explained
by signals bouncing off of the earth's surface.

                                                Dan KL7Y 


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