Topband: Top-band Prop along grayline

[Bill Tippett]

Hi Tom and John,

At 09:22 AM 3/11/05, Tom Rauch wrote:

>"Longpath" strongly implies the path is opposite the
>shortest path, or the longest possible straight path. We can
>be sure that isn't the case, that it is really just a skewed
>or bent path. All we know is the path is a little longer
>than the direct great circle path.

         Here we go with our every few year semantic
discussion.  "Long path" has long been used (since
~1976 at least) to mean approximately 180 degrees...
otherwise wouldn't it be called "longest" path?  ;-)  In
fact, I'll bet there are very few cases on the low bands
of pure 180 degree long path.

         "Skew" path is OK but I feel it is important to
distinguish two very different types of skew paths.  One
is what I call geomagnetic skew, which skews paths
away from either auroral zone toward the equator.  The
other (what I call long path) could be called twilight
skew, since it occurs around periods of relatively low
common darkness.  On 80 meters and higher, the
latter is very obvious since signals may be direct path
well before the twilight period, then shift to "long path"
as twilight approaches, and then shift back to direct
path in full daylight.  I've even seen this on 160 with
some of the better stations like XZ0A.

>All this gives people something to speculate about. That's a
>good thing as long as we remember most longpath claims are
>not actually longpath, but some distance from slightly
>longer than shortpath to not as long as true longpath. It is
>quite common here for me to hear JA's at sunrise via W or SW
>path, up to 90 degrees from NW. That isn't longpath, it's
>just a bent path.

         This is geomagnetic skew which has been well
described by Carl K9LA in the article below.  I've never
seen it more than about 90 degrees even with Kp = 8.  I'm
still hoping for an equivalent article about twilight skew,
but based on actual measurements of the signal path in
the ionosphere rather than theory only.

W1FV wrote:
 >While it would be very interesting to know how the signals actually 
propagate between the end points, in a sense it's academic.  From a 
practical standpoint we only need to know which direction to point our 
receiving and transmitting antennas to work the stuff and let nature take 
care of the rest.  :-)

         ...amen, Amen, AMEN!

                                 73,  Bill  W4ZV

http://users.vnet.net/btippett/long_and_skew_path_articles.htm
(K9LA's article re geomagnetic skew is second one down)