Topband: one-way propagation

[James Wolf]

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 at w8ji.com] 
Sent: Tuesday, December 04, 2012 6:45 AM
To: jbwolf at comcast.net; topband at 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