TopBand: From the bit bucket

[Tom Rauch]

> Date:          Mon, 23 Mar 1998 22:20:23 -0900 (AKST)
> From:          Dan Robbins <kl7y@alaska.net>
> Subject:       Re: TopBand: From the bit bucket
> To:            topband@contesting.com

Hi Dan,

Thanks for the great post. Out of ALL of us, you are in the best 
position to know what really happens.

This issue is a lot like the elevated radial issue. Some things are 
simply too difficult to measure, and so we must determine the results 
by CAREFUL tests and measurements that we can make, not personal 
guesses or "feelings".

When a careful measurement disagrees with the model, the model must 
be flawed.

> I recently pointed out to ON4UN that most propagation programs assume a
> fixed value of earth reflection loss, something like 2-3 dB per hop which is
> a compromise between the land value (several dBs) and the sea water value
> (which is a very small fraction of a dB on 160 meters for common angles).
> For a long over water path (my radar example was mostly over water) the
> actual signal levels may be as much as 15-20 dB or more stronger than what
> the program predicts for such a path length.  Most anecdotal ducting tales
> are suspiciously on long, over-water paths.

An observation I also made and mentioned a while back. The ducts are 
nearly always over a mostly saltwater path.
  
> In the case of NL7Z/K1ZM, it could be that there was a common backscattering
> area somewhere around, say, the HC8 area.  This would be a mostly all water
> path for both parties. The amount of signal backscattered on the lower freqs
> can be very dependent upon the ocean state - smooth as glass and there is
> very little backscatter, but if the swells are just right in direction,
> spacing, amplitude, length, etc., then the back- or sidescatter can be
> appreciable.  OTH radars can easily determine ocean wave velocity and some
> kind of idea of the sea state thousands of miles away by the use of
> backscattered signals.  Given that the direct path between K1 and KL7 was
> probably heavily absorbed, a backscatter path would certainly be feasible.

It was observed by TWO of us here in GA, and I could hear my own 
dits echoing back when I beamed southwest.  I pinged the SW, and got 
an echo. I pinged the NW, and there was none.

The very next day I observed the same exact thing with a California 
station (I think N6RO). He was echoing when I beamed SW, and when I 
pinged the TX I could again hear the last edge of a dot echoing back 
far far above noise level.

> Living under the auroral belt means dealing with these strange paths on a
> regular basis.  If there had been a strong direct path between KL7/K1 nobody
> would have noticed another signal peaking from the wrong direction....

When I beamed towards the KL7, and the N6, the echo disappeared.

Your analysis makes great sense when what I observed here is 
considered. The ducting stuff has never made sense, although I 
haven't ruled it out.

Since you are the one closest to having a true actual picture of 
paths, I have to " buy"  your observations.

73, Tom W8JI
w8ji.tom@MCIONE.com

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