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TopBand: Re: N7DD to A45XR

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Subject: TopBand: Re: N7DD to A45XR
From: (w8ji.tom)
Date: Sat, 06 Feb 1999 07:23:24 -0500
Thanks Dan for the post that makes the most sense to me.

> All in all, a skew path seems the most logical.  First, it wouldn't take
> a lot of skew.  Second, a skew path avoids the daylight dilemma of the
> long path.  Third, a skew path would avoid the auroral attenuator. 
> Finally, a skew path would be consistent with the pattern of the
> beverage, unlike the short path. 

I tried to post this yesterday, but never saw it appear:
> Looking at the geometric trace of a path and that of the
> terminator is one thing.  One can use the numerical details of the
> path, with the aid of a Nautical Almanac, to work out the solar
> elevation along the path.  But just looking at the terminator and
> talking about a heading is something else, open to considerable
> error and misinterpretation of the path relative to sunlight.

I hope I understand what you are saying. My observations about direction
agree with MANY other people on top band. I often hear signals that are
long distances away on paths that "make no sense" and that might wrongly be
construed as true "longpath". 

I have almost zero faith that these paths are arrow straight paths, like we
see in propagation via vacuum or air.

> I have used various locations in Oman but always seem to come up
> with the same result, a major part of the long-path is in sunlight
> (due to summer in the southern hemisphere). 

True, but if the ionosphere bends or scatters the signal along the
terminator the result is something longer than shortpath and perhaps
shorter than true longpath.

 All bets about path distance are OFF. Since a path can bend, the path can
be any distance. In all likelihood, it is NOT the exact opposite of short
path (true longpath).

For example, the radio distance to JA is probably considerably shorter than
the southeast longpath would produce and distances sometimes claimed. I
expect that to be true, because I hear the JA's, on rare days, northeast at
sunset. Northeast is not longpath. The only distance we can be sure of is
the distance is absolutely longer than shortpath. How much longer we have
no idea because we can't follow the propagation path from end-to-end and
validate the distance.

Even southeast might not be longpath, because I'm sure the signal bends or
skews more than propagation experts think. I know that because on rare days
I hear Europeans, even the western and southern Europeans, nearly due east.
I hear VK's anywhere from southwest to northwest, and my dozens of QSO's
with VS6DO almost never were "short path" in heading.  It's a heck of a lot
more bending than 5 degrees. More like a gradual continuous curve in a
train track than an abrupt and well defined 5 degree overall slew.

 > But if one follows the whole path, after leaving N7DD's QTH it
> goes from his dawn, into sunlight around the equator at 117
> West Longitude and then back into darkness around 28 South
> Latitude, 68 East Longitude.  So for an interval covering 175
> degrees of longitude in the southern hemisphere, the path had
> solar illumination on it, peaking at 80 South Latitude and
> displaced poleward from the terminator by about 777 km.

True if the path is straight. Like you, I doubt that is true. "Longpath" is
a misleading term, since by definition it implies the longest path possible
(and distances claimed often wrongly quote those numbers). I disagree with
the postulation of antennas "playing tricks", and I also disagree with
claims a certain general directional heading means it is true longpath. A
more correct term would be "longer path".
> As for signal skewing, one can look at Cary Oler's article in CQ to
> see how small the angular deviation is in a dark ionosphere.

I respectfully disagree. I can't "see" my signal's propagation angle, or
anyone else's, in any article. The only thing I can "see" is the model used
for propagation. If that model does not allow for actual observations that
are made, the model is flawed. I can say that with 100% certainty because I
know the signal arrives from directions that could only happen if the
signal skewed and bent, and NOT just in the auroral zones, more than a
total of five degrees. Europeans coming from the east are a lot more than a
simple 5 degree bend, unless that refers to the angle of a potentially
continuous maximum bend along the path (meaning from any single point the
bend from that point could be as much as 5 degrees).
> All in all, as I look at the two paths, 13,800 km short-path in
> darkness the entire way as compared to 26,200 km long-path in
> sunlight a good part of the distance, I cannot escape the simple
> conclusion that it was not a long-path contact. 

Here we agree. I have no idea if it was a 26,000 km longpath, and I
strongly doubt anyone else does. I suspect most of these claimed
"longpaths" are neither long nor short, but somewhere in-between. A longer
path than short path, by an unknown amount.

So maybe we all agree. It isn't really true longpath, and certainly isn't
shortpath. Let's face it, when the signal hits the highway we all have no
idea what route it takes. All we know is the approximate direction it was
last seen heading, if we are lucky. Accurate distance records are only
assured by knowing propagation always takes more than short path distance,
how much longer is just a wild pi-in-the-sky guess.

When I heard JA's at sunset, or VK6HD, all I know is it is further than
when I hear them at dawn.

73 Tom 

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