Tom,
It is a known that the ionosphere is not a perfect sphere. It is always moving
and it is lumpy and tilted. Together these occurrences can cause focusing and
defocusing of the wave due to deformities especially if they are concave or
convex. One-way-propagation can reveal itself as a deep and/or prolonged fade
on only one end of the link because of the aforementioned reasons. Of course
fades can be caused by other reasons, such as multiple paths, etc.
Jim, KR9U
-----Original Message-----
From: Tom W8JI [mailto:w8ji@w8ji.com]
Sent: Tuesday, December 04, 2012 6:45 AM
To: jbwolf@comcast.net; topband@contesting.com
Subject: Re: Topband: one-way propagation
> To expand a little on Carl's explanation, the ionosphere is not as
> isotropy as we commonly imagine - in that it is not a nice smooth
> balloon shaped surface to bounce a signal off of. Instead, there are
> varying degrees of irregularity, not unlike a sandy desert where the
> wind moves the landscape around and creates moving peaks and valleys.
> So imagine the ionosphere in this condition when a signal from one
> direction has a nice reflection down to the receiver, but in the other
> direction, it is reflected at a different angle and lands somewhere else.
>
> Jim, KR9U
>
There is no possible combination of refractions or reflections that is not
reciprocal in both directions.
If there is a mechanism at work, it is at an entirely different level than
simple multiple reflections.
After 50 years on 160, I'm still unsure if one way propagation exists. All of
the "one way" I have seen and taken the time to look at involves noise levels,
QRM, or just the capability of the stations.
For example, prior to sunset here my local noise is very low. Even on a quiet
winter night in a quiet direction, noise floor increases 10-15 dB as it gets
darker and conditions improve. I can hear Europeans that I have no hope of
working (on 40 meters this happens all day long). Their noise is high (even in
a quiet location) because it is dark. As it gets darker their signals come up,
and so does my noise and QRM, but eventually they hear me.
The opposite occurs at sunrise. There is the same noise floor drop after
daylight. This means I can hear JA's working west coast stations long after
they stop being able to hear me.
Local storms and local QRM, and the direction of that stuff, is also is a huge
factor in reciprocity.
Sorting it all out is very complicated, and involves far more than observing
"sometimes people at one end don't answer". Sorting it out would involve and
**require** calibrated observations of absolute signal levels and noise levels
at both ends. I think this is why one way prop is, at best, arguable.
73 Tom
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