dxAce wrote in message ...

Regardless of how some SWL's antennas are aligned, the physics of wave propagation dictate how the signal will
arrive, not the antenna position. But... if one has an antenna, or antennas to position properly, they will be
able to take greater advantage of the direction the signal is coming from, thereby getting better reception.

Now go ponder that grey line map again.

I know you'll get it yet! It's actually very simple.

dxAce
Michigan
USA

Here are some websites that not only describe some things about
grayline propagation, but also clearly show it's true shape and why a
flat map will portray a grayline differently than its true shape
(which is, in actual fact, a great circle with an approximately
85-minute-wide width along the sunrise/sunset terminator).

http://www.iri.tudelft.nl/~geurink/grayline.htm
http://www.kc4cop.bizland.com/propagation_gray_line.htm
http://www.cpcug.org/user/wfeidt/Misc/n4kgprop.html

There are numerous websites also that but discuss how, through
geomagnetic-solar-induced electron gradients, radio propagation may be
diverted from its normal great-circle path onto *another* and
different great circle pathway - and how, if one is lucky, one of
those great circle paths may a grayline terminator that will deliver a
wondrous DX signal to your ears.

Some other websites even go on to say that, unless you are
running/listening to CW or high-powered SSB, these diversions are not
always likely to yield good results, because much is still lost when
the RRF shifts pathways.

Radio waves, like light waves (which they really are), do not just
bounce around as they like depending upon random events and
conditions. They travel in straight lines, and are affected (under
earthbound conditions) only by reflective and refractive factors -
ionospheric skip keeps them near the earth, and geomagnetic electronic
gradients can veer them. Absent the latter, within a very narrow
bound, those signals will assume a great circle pathway -

Which brings us to the tentative conclusion that DxAce's most common
and likely reception pathway for Diego Garcia is a great circle route,
and a trace of that route is going to give you, for practical
purposes, a pathway that closely approaches the north or south
geomagnetic pole. If it sounds watery one day and not so watery the
next, it is because the interaction between the solar flux and the
earth's geomagnetic field varies from day to day - providing, perhaps,
modest skewing or rippling of the signal.

Based on examining a number of pretty well-documented websites, and on
what I know from astronomy and geophysics, I have few doubts about
this description, which is admittedly general as it is.

I would suggest that anyone who is unfamilar with maps and
projections, and the distortions they introduce into plots of
spherically-coordinated surfaces and lines, should look at some
websites on maps. It is fascinating how maps and their various
projections can be used to show specific points, while at the same
time totally distorting others.

Try Google searches for "map projection(s)" and for "skewed" or
"grayline" + "propagation" as well.