Topband: Top-band Prop along grayline

[Bill Tippett]

K2TQ:
 >John's post about long-path to Japan on top-band is very interesting. It
would seem, as John mentioned, to be very rare.

         Long path is not as uncommon as you might think.  In fact
it's "normal" mode for contacts on the other side of the auroral oval.
See here for several examples:

http://users.vnet.net/btippett/dx_aid_plots.htm

The thing that makes it uncommon for W1>JA, as K1ZM already explained,
is the very narrow window of common darkness between W1 and JA.  There
is an excellent graphical illustration of this by JA3ONB in Figure 14-1
on page 14-3 of K1ZM's book DXing on the Edge.  It graphically shows the
common darkness time between JA3ONB and both Jeff's NY and Cape Cod
QTH's by UTC and by date.  It appears that the maximum common darkness
for NY is about 30 minutes and for Cape Cod about 45 minutes.  No doubt
extreme (ayuh!) Northeastern Maine might have a bit more.  30-45 mins is
at the lower limit of common darkness I've seen on my long path QSO's
(which average 90 minutes and are at 53% into common darkness):

QSO                     Date    UTC     Com Dark        QSO @ %

Sunrise paths:
UA9UCO - W0ZV           29SEP87 1232    59 mins         61
JJ1VKL/4S7 - W0ZV       28DEC91 
1335   109              56
3W5FM - W4ZV            06JAN00 1143   107              55
XZ0A - W4ZV             21JAN00 1156    62              50
XU7ACB - W4ZV           05DEC01 1119    93              40
JT1CO - W4ZV             03FEB03 1127   145              64
HS72B - W4ZV             03DEC04 1152    86              74

Sunset paths:
9V1XQ - W4ZV            13JAN96 2309    42              50
S21XX - W4ZV            04FEB97 2320   106              26

Average:                                90              53


         As to how this path works, it has been discussed to death
before with no real answers IMHO.  I've seen a lot of weird hypotheses
but nobody really knows since they have not tracked the actual signal
path once it leaves the two end points.  What I do know is how to use
this mode.  It is very consistent at about 210 degrees bearing before
sunrise and about 150 degrees after sunset.  This is also consistent
across all of North America, independent of actual 180 degree great
circle bearings and very consistent with my experience on 80-20m.  That
knowledge (i.e. WW2Y now knows to listen SSE after sunset) plus knowing
the path tends to peak around 50% of the way between the sunrise/sunset
times is all you really need to know to effectively use it.  I'll leave
the hypothetical and theoretical discussions to follow to others!

                                                 73,  Bill  W4ZV