[NLRS] Tropo Maps

[Ford Peterson]

I previously wrote:

> Bob tells me that the weather aspects have been studied, and interesting anomoly do happen, but 
> not in a documented way--especially at MF.  

By the way, for those unfamiliar with the 'weirdness' that occurs on Topband, a brief summary of the aspects may be of interest.

Path skewing...  Signals arriving from EU are stronger when beaming SE.  And it is a bi-directional path.  The traditional NE path is not open to the US many-a-night.  But the SE path is.  Ditto for Australia and Japan.  Normally, due West (for AU) and north of West (for JA) would be the appropriate direct path.  But the strongest signals often arrive from the SW. 

Spotlighting...  Stations seem to appear suddenly out of the ether and are very close in proximity to one another.  Paths into FL, WV, GA, SC, are the most notible from here.  But the phenomena cannot be easily explained.  In fact, many do not believe it to exist because they have not experienced it.  

Path nulls...  Signals at two different stations the same distance from the target may appear with good intensity at one station, and be null at the other.  

Terminator effects...  Sunrise and sunset play a significant role in signal peaks.  Many places on the planet can only be worked through a very small window of only a few minutes.  But this effect is not consistant either.  So other (as of yet unknown) factors come into play.

Reverberations...  Signal paths can become multipath.  But the delay in signal is far greater than can be explained assuming a complete long-path around the earth.  A single signal can arrive as many as two or even three times like they were processed by a reverb.  I personally have heard this effect many a time.  It's almost impossible to copy as all the signals are the same intensity and identical in frequency (since they are one).  It sounds like two or three stations calling with a zero beat.  

Aurora...  The presence of Aurora is well known to completely destroy MF propagation.  Yet just the other night, EU was working the west coast of the US (and only the west coast) during a period of high A and K index.  So other factors are in play.  I was hearing norther Russia stations with good intensity.  Both he and I were under the cloud of the Aurora, but he was near the sunrise terminator.

Will weather play a role in any of this?  Who knows.  But Jon-W0ZQ has reported publically that he has experienced some of the MF effects listed above, and noted simultaneous openings on VHF.  So maybe the effects are related.  But the mechanism in play with the physics involved remains a bit of a mystery.

Ford-N0FP
ford at cmgate.com